In these consolidated appeals, we consider again the proper application of pro tanto and pro rata credits. Appellants Elena M. Paul and The George Washington University (GWU) ask us to review two post-trial orders made after a jury verdict awarding medical malpractice damages to Paul in a suit against Dr. Charles J. Bier, her private physician. According to Paul, the trial court erred in concluding that Dr. Bier was entitled to a pro tanto rather than a pro rata credit against the verdict as a result of Paul’s settlement with GWU during trial. GWU asserts that the trial court abused its discretion in denying its post-verdict motion to assert a cross-claim for contribution against Dr. Bier. Because joint liability was not established between the alleged joint tortfea-sors, Dr. Bier and GWU, we agree with the trial court’s decision to apply a pro tanto credit to the jury’s verdict. As Paul had already been compensated by the settlement with GWU in the full amount of the jury verdict, Dr. Bier had no outstanding obligation to pay Paul. We also hold that the trial court did not abuse its discretion in denying GWU’s motion to file a cross-claim for contribution against Dr. Bier on the ground that the untimeliness of the motion was prejudicial to Dr. Bier, the nonsettling party.
I.
In 1994, Elena Paul sued Dr. Charles Bier and GWU, the employer of a second physician, Dr. Druy, to recover damages for medical malpractice. During trial, GWU settled with Paul in the amount of $2,000,000 and Paul’s case against GWU *42was dismissed with prejudice1 on July 18, 1996.2 GWU denied liability in the settlement agreement.3 In the event GWU was sued for contribution by Dr. Bier, however, the agreement required Paul to stipulate that GWU and its employees were “active tortfeasors ... for the purpose of determining the rights of the remaining non-settling defendant [Dr. Bier] to a complete or partial set-off.” The settlement agreement also required Paul to indemnify GWU for any amount it may be liable in contribution to Dr. Bier.
The trial continued against Dr. Bier and, on July 29, 1996, the jury returned a $2,000,000 verdict in favor of Paul. Dr. Bier did not file a cross-claim against either GWU or Dr. Druy for contribution or indemnification, but, instead, immediately after the jury’s verdict, made a motion for the application of a pro tanto credit against the verdict of $2,000,000, the amount that Paul had received in settlement from GWU. Paul opposed the motion arguing for application of a pro rata credit in the amount of $1,000,000, to reflect what Paul claimed was GWU’s one-half share, as joint tortfeasor with Dr. Bier, of the jury verdict. On September 16, 1996 the trial court ruled in favor of Dr. Bier, and applied a pro tanto credit against the verdict. As a result, appellant Paul’s recovery was limited to the $2,000,000 settlement amount already paid by GWU, and Dr. Bier did not have to pay anything. On October 24, 1996, settling defendant GWU sought leave of the court to file a cross-claim for contribution against Dr. Bier, which the trial court denied as untimely. Paul appeals from the order applying a pro tanto credit.4 GWU appeals from the trial court’s refusal to allow the cross-claim for contribution.
II.
A. Paul’s Appeal (96-CV-1495): Pro Tanto v. Pro Bata Credit.
A pro tanto credit is based on the actual settlement amount, “dollar-for-dollar,’’while a pro rata credit is based on proportionate shares of liability among joint tortfeasors. See Berg v. Footer, 673 A.2d 1244, 1248-49 (D.C.1996). Appellant Paul opposes the application of a pro tanto credit of the settlement amount against the verdict on the ground that it results in the unjust enrichment of a nonsettling defendant, such as Dr. Bier, when, as here, the amount of the verdict equals the amount of the settlement the plaintiff reached with another defendant. In addition, Paul asserts that a pro rata credit is appropriate in this case because only one of her two liability claims was submitted to the jury, and therefore the jury verdict represented only one-half of the damages arising from these claims. The question of “[h]ow to credit the judgment entered upon a jury verdict against a nonsettling defendant with the proceeds a settling defendant paid to the plaintiff’ is purely a question of law, which this court reviews de novo. Berg, 673 A.2d at 1247 (citing Bertram v. Freeport McMoran, Inc., 35 F.3d 1008, 1019 (5th Cir.1994)). We stated in Berg that a nonsettling defendant is *43entitled to a pro tanto credit for the amount paid by settling defendants who are not joint tortfeasors, see 673 A.2d at 1245, and to a pro rata credit based on the nonsettling defendant’s right of contribution against a settling joint tortfeasor, see id. at 1248.
Paul’s complaint alleged that separate acts of negligence by Dr. Druy, a GWU employee, and Dr. Bier, her private physician, combined to proximately cause injury, namely post-phlebitic syndrome, as a result of vascular damage to her left leg. After presenting her case to the jury against all the defendants, Paul settled her negligence claim against GWU, and its employee, Dr. Druy, for $2,000,000, and they were dismissed as defendants in the case. The jury then found in favor of Paul against Dr. Bier after finding that Dr. Bier’s actions were a proximate cause of Paul’s injuries, and awarded her $2,000,000 as compensation for her injuries. Paul’s claim that the jury verdict compensated for damages solely attributable to Dr. Bier, ie., that it was not intended as full compensation for her injuries, is not borne out by the record.5 The jury valued all of Paul’s injuries at $2,000,000 and assessed those damages as attributable to Dr. Bier’s negligence. Paul received $2,000,000 as a result of the settlement agreement with GWU. Thus, Paul was satisfied by the settlement to the full extent of the damages found by the jury.
Notwithstanding that she has received compensation to the full extent of the jury’s $2,000,000 verdict, Paul contends that she is entitled to the benefit of a pro rata credit under our Berg opinion. We recognize that Paul would have benefitted if the trial court had applied a pro rata rather than a pro tanto credit, in that Dr. Bier would have been required to pay Paul an additional $1,000,000,6 reflecting his proportionate share of liability. In Berg, this court applied a pro rata credit, which in the circumstances of that case resulted in total compensation to the plaintiff in excess of the jury’s verdict,7 noting that “the law contains no rigid rule against overcompensation.” Id. at 1256 & n. 19 (quoting McDermott, Inc. v. AmClyde and River Don Castings Ltd., 511 U.S. 202, 219, 114 S.Ct. 1461, 128 L.Ed.2d 148 (1994)). This holding, however, was not *44based on the rationale that the plaintiff was entitled to compensation in excess of the jury’s verdict, but rather that, in spite of that consequence, “consistency with established precedent applicable to settlements with joint tortfeasors weighs in favor of’ applying a pro rata credit to the jury verdict “even though the nonsettling defendant’s pro rata contribution to the amount of the jury verdict, when added to the amounts recovered in settlement, will result in a plaintiffs recovery that exceeds the verdict.” Berg, 673 A.2d at 1257. The court expressly declined to make application of a pro rata credit depend on the relative settlement and verdict amounts in an individual case, noting that “[m]aking particular credit rules contingent upon the relative amounts of the settlement and the jury’s verdict ... would only increase uncertainty and make it even more difficult for litigants to negotiate settlements.” Id. But see Rose v. Associated Anesthesiologists, 163 U.S.App.D.C. 246, 250, 501 F.2d 806, 810 (1974) (limiting the amount of pro tanto credit “so as to assure that the defendant held liable in the litigation does not pay less than his equitable [pro rata ] share”).8
In short, the injured patient in Berg was no more than an incidental beneficiary of this court’s decision to adhere to the rule that when a settling defendant is a joint tortfeasor, the nonsettling defendant is entitled to a pro rata credit against the jury’s verdict. See Berg, 673 A.2d at 1257 (citing Martello v. Hawley, 112 U.S.App.D.C. 129, 132, 300 F.2d 721, 724 (1962)). Although application of a pro tanto credit means that the plaintiff will not receive a windfall benefit, the court’s decision to apply a pro tanto credit in no way reduces that to which the plaintiff is entitled, compensation in the amount awarded by the jury. Whether Paul will receive that windfafi depends exclusively on whether a pro. rata credit should have been applied in order to vindicate the right of contribution between the settling and nonsettling defendants as joint tortfeasors. We now turn to that issue.9
A threshold obstacle to Paul’s claim that a pro rata credit should have been applied to the verdict rendered against Dr. Bier is the absence of either a judicial determination or a stipulation, see Berg, 673 A.2d at 1251 & n. 13; Lamphier v. Washington Hasp. Ctr., 524 A.2d 729, 733 & n. 5 (D.C.1987), that GWU is a joint tortfeasor with Dr. Bier. Because GWU settled mid-trial and was dismissed from the case, and it did not raise the issue of contribution until after the jury’s verdict, see infra, there was no court adjudication that GWU and Dr. Bier were joint tortfea-sors. GWU’s post-trial unilateral acknowledgment of liability in its cross-claim for *45contribution, is not supported by any stipulation 10 and is contradicted by its blanket denial of liability in the settlement agreement. See supra note 3. As we have explained, for a nonsettling defendant to receive a pro rata credit, the liability of the settling defendants must be established either by adjudication or by stipulation between the plaintiff and the settling party. See Shannon, supra note 9, 696 A.2d at 1367 (citing Berg, 673 A.2d at 1251 & n. 13); Washington Hosp. Ctr., supra note 5, 722 A.2d at 336 (noting the “essential prerequisite for entitlement to contribution is that the parties be joint tortfeasors in the sense that their negligence concurred in causing the harm to the injured party”) (citations omitted); Washington, supra note 9, 579 A.2d at 187 (explaining that the right to contribution is contingent upon a finding of joint liability); Lamphier, 524 A.2d at 733 & n. 5 (noting that the liability of the settling tortfeasor must be judicially established as a predicate to asserting the right to contribution) (citing Otis Elevator Co. v. Henderson, 514 A.2d 784, 786 (D.C. 1986) (per curiam)). As Paul’s argument for a pro rata credit derives from the right to contribution of the joint tortfeasors, the same requirement applies if the plaintiff, rather than the nonsettling defendant, requests a pro rata credit. In the absence of either an adjudication or stipulation that GWU and Dr. Bier were joint tortfeasors, the trial court did not err in granting Dr. Bier’s request to apply a pro tanto credit.11 Cf Berg, 673 A.2d at 1250-51 (stipulation sufficient where the settling tortfeasor admitted to liability in pretrial statement stipulation of facts to the court and “[a]ll parties, including [nonsettling tortfeasor] agree that [settling tortfeasor’s] stipulation of liability is enough to make it a joint tortfeasor”).
B. GWU’s Appeal (97-CV-50): The Settling Defendant’s Cross-Claim, for Contribution.
GWU asserts that the trial court abused its discretion in denying its motion to file a cross-claim for contribution against Dr. Bier following the jury verdict. It maintains that there is no equitable reason why it should be required to pay the full amount of the jury verdict while Dr. Bier receives a “free pass,” and that such an inequitable result conflicts with this court’s longstanding policy of encouraging out-of-court settlements. As we noted earlier in connection with Paul’s appeal, a question at issue in this case is whether, even assuming the timeliness of GWU’s motion, GWU could claim a right to contribution as a joint tortfeasor given that its liability to the plaintiff was neither judicially determined nor the product of a stipulation by the parties. See supra notes 10 and ll.12 Assuming that GWU, as a settling defendant, had a right of contribution against the nonsettling Dr. Bier, we recognize that *46the settling defendant must have available a procedural mechanism to establish the predicate joint tortfeasor liability, even though as a result of settlement, it is no longer party to the lawsuit. This court, however, has yet to decide the issue whether a settling defendant has a right to contribution. See, e.g., Washington Hosp. Ctr., 722 A.2d at 342-43 & nn. 13-15. We do not reach either question, however, because we hold that, even'if GWU is a joint tortfeasor with a right to contribution, the trial court did not abuse its discretion in disallowing the cross-claim on the ground that GWU’s failure to timely assert its right to contribution was prejudicial to Dr. Bier, the nonsettling defendant.13
The decision whether to grant or deny a motion to file a cross-claim under Civ. R. 13(a) or to amend a pleading under Rule 15 is within the sound discretion of the trial court, and we review the decision for abuse of discretion. We are mindful, however, of the liberal construction we place on pleading rules to achieve substantial justice over formalism. See Goldkind v. Snider Bros., Inc., 467 A.2d 468, 474 (D.C.1983); Eskridge v. Jackson, 401 A.2d 986, 988 (D.C.1979) (per curiam); Eagle Wine & Liquor Co. v. Silverberg Elec. Co., 402 A.2d 31, 34 (D.C.1979). Although a trial court may not deny a motion to amend the pleadings simply because of undue delay, “the lateness of a motion may well provide the predicate for a proper determination that prejudice to the opposing party would result if an amendment were allowed.” Eagle Wine & Liquor Co., 402 A.2d at 35; see also Gordon v. Raven Sys. & Research, Inc., 462 A.2d 10, 13 (D.C.1983) (no abuse of discretion in denying leave to amend complaint requested eighteen months after filing and after close of discovery, noting that movant gave no reason for delay and opposing party would be prejudiced by having to begin anew the pretrial and trial proceedings).
In evaluating the timeliness of GWU’s motion to file a cross-claim and its potential prejudice to Dr. Bier, we start with the familiar principle we have already discussed in connection with Paul’s appeal that a right of contribution does not arise “without a finding that the party seeking contribution is a joint tortfeasor along with the party from whom contribution is sought.” Hall, supra note 13, 621 A.2d at 850. GWU argues that it did not have a right of contribution against Dr. Bier until he was found to be a tortfeasor, and thus, that GWU could not have filed its cross-claim before the jury’s verdict. Here, GWU sought leave to file its cross-claim not only three months after the jury’s verdict but also five weeks after the trial court had ruled on Dr. Bier’s motion for a pro tanto credit. Thus, GWU also argues that its contribution claim was not untimely because it did not accrue until after the trial court awarded a pro tanto credit to *47Dr. Bier and it became clear that GWU had paid a disproportionate share of the liability. According to our case law, “a right of contribution accrues when two or more parties are joint tortfeasors.” Hall, supra note 13, 621 A.2d at 850 (citations omitted), but is “enforceable only after the one seeking it has been forced to pay.” Bair v. Bryant, 96 A.2d 508, 510 (D.C. 1953). Although we do not decide whether GWU was a joint tortfeasor, we note that if GWU was not a joint tortfeasor then it had no right to contribution, and if, as GWU subsequently postulated, it was a joint tortfeasor, its right of contribution (assuming that settling defendants have such a right) would have become enforceable at the time, while the litigation against Dr. Bier was still in progress, when it agreed to pay Paul $2,000,000. Moreover, it would not be the trial court’s application of the pro tanto credit in mid-September 1996, but the verdict at the end of July 1996, that would have alerted GWU to the disproportionality of its settlement with Paul.14 We therefore are not persuaded that GWU had a reason, based in law, to delay asserting its claim of contribution.
In Washington, this court held that a nonsettling defendant is barred from filing a cross-claim for contribution post-trial in the parallel situation to the one in this appeal, where the nonsettling defendant’s share of liability after application of a pro tanto credit was more than its pro rata share. 579 A.2d at 186-88 & n. 11. Even though the right to contribution does not accrue until the nonsettling defendant’s status as joint tortfeasor is established, a cross-claim for contribution against a settling defendant must be asserted before the verdict is rendered as the claimant is expected to “safeguard any legitimate claim it might have to lessen the burden of a plaintiffs verdict” by asserting it during trial. Id. at 188 (citation omitted). Likewise, in Hall v. General Motors Corp., 207 U.S.App.D.C. 350, 647 F.2d 175 (1980), the court indicated that where a nonsettling defendant has a clear opportunity to clarify the issue of a settling defendant’s liability by filing a cross-claim during trial and does not do so, the nonsettling defendant is not entitled to a pro rata reduction of judgment based on joint liability. See Id. at 358-59, 183-84, 647 F.2d 175; see also Berg, 673 A.2d at 1250 n. 10 (noting non-settling defendant’s responsibility to file cross-claim against settling defendant in principal action to ensure right to a pro rata contribution); Otis Elevator Co., 514 A.2d at 786 (concluding that where a non-settling defendant does not cross-claim against a settling defendant for contribution, and neither the judge nor the jury ever considered liability of settling defendant, nonsettling defendant is only entitled to pro tanto contribution). In formulating this rule, we have focused on the prejudice caused by the nonsettling defendant’s late assertion of a claim for contribution on the settling defendant, see Berg, 673 A.2d at 1250 n. 10, and on the plaintiff, see Washington, 579 A.2d at 188 (because “[pro rata ] credit’s consequences are visited upon the plaintiff .... injured party in settling with one tortfeasor effectively bears the burden that otherwise would fall upon the settling tortfeasor to make contribution”).
We see no reason why the same principle should not apply when it is the settling defendant claiming contribution. As the trial court aptly noted:
If equity bars a late-filed cross-claim for contribution by the non-settling defendant even where its share of liability after a pro tanto credit is more than its pro rata share, it is hard to see why equity should entertain an after-the-fact *48cross-claim by the settling defendant when the verdict goes the other way.
Like a nonsettling defendant, a settling defendant sleeps on its rights when it fails to file a timely cross-claim to determine the respective liability of the defendants. Fairness dictates that all defendants, whether they choose to settle or litigate, file cross-claims for contribution before the verdict in order to give notice to other defendants that they will be required to pay their fair share of damages to a joint tortfeasor in the event that they are found hable.15 We recognize that a nonsettling defendant does not need the spur of a claim for contribution to defend itself against a plaintiffs claim of liability. The manner of defense and trial strategy may be different, however, in light of a claim for contribution by an alleged joint tortfea-sor. In this ease, as we noted earlier in consideration of Paul’s appeal, there was no request to apportion the injury attributable to Dr. Bier from that attributable to GWU. See supra note 5. Although there can be no doubt that it was in Dr. Bier’s interest even prior to GWU’s settlement to separate its responsibility from that of GWU if it could have reduced his potential liability to Paul as a -result, Dr. Bier may have considered that the most effective defense with the jury was one that denied all liability on his part and attempted to minimize the injury alleged by Paul. Had Dr. Bier been put on notice of GWU’s intent to claim for contribution, he would have had an incentive to build a case during trial that separated his liability from that of GWU if he knew that joint tortfea-sor liability would be a central feature of his responsibility to GWU. See Washington, supra note 9, 579 A.2d at 188 (noting ways in which plaintiff might have litigated differently in light of request for pro rata credit even if it meant shifting theories before jury).
In this case, were the court to grant GWU, a settling defendant, leave to file its belated cross-claim for contribution against Dr. Bier, in the words of the trial court, GWU would “have all of the benefits of a claim for contribution with none of the burdens that should, in equity, attend such a claim.” Given that the $2,000,000 settlement amount equals the jury verdict, the pro tanto credit protects GWU against any contribution claim by Dr. Bier. Even if GWU’s pro rata share of the verdict had exceeded the settlement amount, and Dr. Bier had claimed a right to contribution, the indemnification clause in the settlement agreement between Paul and GWU ensures that GWU will be shielded from any further contribution. See Rose, 163 U.S.App.D.C. at 250, 501 F.2d at 810 (noting that settling defendants “cannot equitably insist on a continuing involvement in the litigation for the purpose of invoking contribution to lessen their [settlement] payment when they have no exposure to an increase in payment if contribution should be sought from them”). Dr. Bier, on the other hand, would be precluded from filing a cross-claim for contribution against GWU after the verdict. See Washington, supra note 9, 579 A.2d at 187-88. Thus, as the trial court observed, GWU filed its cross-claim only after it was protected from any “downside risk of contribution to Dr. Bier.”
A requirement that all defendants file cross-claims for contribution before verdict is in line with our longstanding policy of encouraging settlements. See, e.g., Moses-Ecco Co. v. Roscoe-Ajax Corp., 115 U.SApp.D.C. 366, 371 & n. 4, 320 F.2d 685, 690 & n. 4 (1963) (citing Martello, 112 U.S.App.D.C. at 130, 300 F.2d at 722, and McKenna v. Austin, 77 U.S.App.D.C. 228, 234, 134 F.2d 659, 665 (1943)). Had GWU filed a timely cross-claim for contribution, *49Dr. Bier would have been put on notice that, should the jury find him negligent, he would be required to pay his pro rata share of the damages award. While this information may not have induced Dr. Bier to settle, especially if he believed that he would be exonerated by the jury, at the very least a contribution cross-claim would have informed Dr. Bier’s strategic choices and should, therefore, have been filed during the course of the litigation. Accordingly, the trial court did not abuse its discretion in denying as untimely GWU’s motion to cross-claim for contribution, filed several months after GWU knew the jury verdict awarding $2,000,000 to Paul and the trial court’s order granting Dr. Bier’s motion for a pro tanto credit against the verdict.16
For the foregoing reasons, we affirm the trial court’s application of a pro tanto credit and denial of GWU’s post-verdict motion to amend its pleadings to include a cross-claim for contribution.
So ordered.
. Prior to settling with GWU, Paul dismissed her claim against Dr. Druy, the GWU physician.
. The settlement agreement between Paul and GWU is dated one week later, July 26, 1996.
. The settlement agreement provides in pertinent part:
Nothing contained in this paragraph of the Agreement constitutes an acknowledgment by George Washington, its agents, servants or employees, that they are or should be hable to the plaintiff or the nonsettling defendant for the claims and causes of action asserted in the lawsuit. George Washington, its agents, servants and employees maintain that they are not liable on any of the claims and causes of action asserted therein.
.Paul had also moved to seal the settlement agreement. The trial court denied the motion to seal as Paul sought to attach the settlement agreement to her opposition to Dr. Bier’s motion for a pro tanto credit. Paul does not appeal from the court’s denial of her motion to seal.
.According to the trial court,
[t]he jury was not asked to apportion the injury caused by defendant Bier’s negligence from the injuiy caused by any negligence of the settling defendants [i.e., GWU and Dr. Druy], and the expert testimony would not have permitted the jury to make such an apportionment had it been asked to do so. Based on the evidence and the court’s instructions, the jury found that defendant Bier's negligence was a proximate cause of [Paul’s] injuries, and that $2,000,000 would fairly and reasonably compensate her for those injuries.
On appeal, Paul contends, without record reference, that the jury instructions on negligence and damages "corresponded directly to the single claim of damages attributable to defendant Bier only.” We see no evidence in the record contrary to the trial court’s determination that Paul did not request that the jury award only those damages caused solely by Dr. Bier, and Paul did not designate any of the transcript for the record on appeal. Indeed, by arguing that the trial court should have applied a pro rata credit, Paul impliedly asserts that Dr. Bier and GWU were jointly liable for a single injury. See District of Columbia v. Washington Hosp. Ctr., 722 A.2d 332, 338 (D.C.1998) (en banc); Berg, 673 A.2d at 1248 (noting that a party who is sole cause of injury is not entitled to contribution).
. This $1,000,000 figure assumes that GWU, and its employee, Dr. Druy, constitute one tortfeasor, and that Dr. Bier, as the second tortfeasor, would be responsible for half of the $2,000,000 jury verdict under a pro rata credit scheme.
. In Berg, after the hospital and laboratory settled for $800,000 and $150,000, respectively, the jury returned a verdict against the nonsettling physician in the amount of $1,406,071. The nonsettling physician obtained a pro tanto credit of $150,000 with respect to the laboratory, which had not been determined to be a joint tortfeasor, and a pro rata credit of one-half of the remainder of the jury verdict (after deduction of the $150,000 pro tanto credit) with respect to the hospital, which was a joint tortfeasor. As a result, the plaintiff received $1,578,035.50, more than the $1,406,071 awarded by the jury.
. The $2,000,000 settlement between Paul and GWU reflected a strategic choice by Paul, who considered "the uncertainty of recovery and of the need for a settlement to help strengthen [her] litigation prospects against a nonsetfler.” Berg, 673 A.2d at 1256 (citing McDermott, 511 U.S. at 221, 114 S.Ct. 1461). Had the jury returned a verdict against Dr. Bier of less than the settlement amount, Paul would have gained “good fortune in striking a favorable bargain with" GWU. Id. (quoting McDermott, 511 U.S. at 220, 114 S.Ct. 1461).
. It is worth noting that had the jury verdict substantially exceeded the settlement amount, and if GWU had been determined to be a joint tortfeasor, Paul could have received less than the full amount of the verdict. This is because Dr. Bier, the nonsettling tortfeasor, would have obtained a pro rata credit against the verdict in an amount equal to the sum to which he would have been entitled in contribution, i.e., half of the verdict, instead- of recovering directly from GWU. See Berg, 673 A.2d at 1250 n. 9. For example, had the jury returned a verdict of $5,000,000, and assuming a pro rata credit of one-half were appropriate, Dr. Bier would have received a $2,500,000 credit against the verdict. Paul would have received a total of $4,500,000: $2,500,000 from Dr. Bier and the $2,000,000 settlement from GWU, which by virtue of its decision to settle with Paul would have limited its liability in the suit. See District of Columbia v. Shannon, 696 A.2d 1359, 1368 (D.C. 1997) ("[A] plaintiff ... must have an opportunity to develop the record in opposition to the claim [for a pro rata credit]”) (citing Washington v. Washington Hosp. Ctr., 579 A.2d 177, 188 (D.C.1990)).
. The settlement agreement provided that Paul, the plaintiff, would stipulate to GWU’s tortfeasor status in the event Dr. Bier sued GWU for contribution. As Dr. Bier did not sue GWU for contribution, Paul was not required to stipulate, along with GWU, to its joint tortfeasor liability. The record contains no indication that Paul sought to enter into a stipulation with GWU that it had committed, jointly with Dr. Bier, medical malpractice with respect to her.
. It is indeed anomalous that in a case where both the plaintiff and the settling defendant desire application of a pro rata credit on the basis of GWU’s status as a joint tortfea-sor, they have not produced the necessary stipulation. At least a partial answer may be found in that in this case, as opposed to in Berg, GWU and the plaintiff disagree on which one of them should receive the benefit of the pro rata credit. We note that although the settlement agreement covers in detail Paul’s financial responsibility to indemnify GWU in the event that Dr. Bier claimed contribution or indemnification against GWU, it is silent on the parties’ respective rights in the situation that developed here, where it was GWU, not Dr. Bier, making a claim for contribution.
.Thus, we disagree with GWU that its motion should have been allowed in order to conform the pleadings to the evidence under Civil Rule 15(b) because the "only relevant factual issue is whether Dr. Bier is liable to Ms. Paul.”
. There is at first blush a question whether, at the time that GWU sought to file a cross-claim against Dr. Bier, it was a "party” to the lawsuit as it had been dismissed with prejudice pursuant to the settlement agreement. See Civ. R. 13(g) (2000) ("A pleading may state as a cross-claim any claim by 1 party against a co-party arising out of the transaction or occurrence that is the subject matter” of the litigation) (emphasis added). Were the claim otherwise appropriate and timely, however, we do not believe that the fact of dismissal of one defendant should preclude GWU from pursuing its contribution claim as a cross-claim in light of our liberal pleading rules. Cf. Hall v. George A. Fuller Co., 621 A.2d 848, 850-51 (D.C.1993) (holding cross-claim for contribution properly dismissed where plaintiff had dismissed all of its claims against all defendants because cross-claim is dependent upon plaintiff’s original claim). With the same purpose of achieving substantial justice, if GWU's late cross-claim was properly denied, a separate complaint for contribution also would be subject to a defense of laches or estoppel. Cf. Chappelle v. Sharp, 112 U.S.App.D.C. 182, 183, 301 F.2d 506, 507 (1961) (per curiam), cert. denied, 370 U.S. 903, 82 S.Ct. 1250, 8 L.Ed.2d 400 (1962). (plaintiff's suit seeking reinstatement as civil servant barred by laches when brought thirty-four and one half months after final administrative action on removal)(citing Arant v. Lane, 249 U.S. 367, 372, 39 S.Ct. 293, 63 L.Ed. 650 (1919)).
. It has been said with respect to accrual for statute of limitation purposes that "the statute of limitations begins to run against the right to contribution only from the time of the disproportionate discharge of the common obligation by one of the common obligors.” Bair, 96 A.2d at 510 & n. 5 (citing Knell v. Feltman, 85 U.S.App.D.C. 22, 25, 174 F.2d 662, 665 (1949)).
. The rule is also fair to plaintiffs. See Shannon, supra note 9, 696 A.2d at 1368 (noting that a defendant’s claim to a pro rata credit is viewed more favorably when it is swiftly asserted as a plaintiff is entitled to the "earliest possible notice of a defendant's intent to claim a pro rata credit but also must have an opportunity to develop the record in opposition to the claim”) (citing Washington, supra note 9, 579 A.2d at 188).
. GWU maintains that any prejudice to Dr. Bier resulting from its post-verdict claim for contribution is outweighed by the fact that Dr. Bier, the only adjudicated tortfeasor, will owe nothing towards the verdict after the application of a pro tanto credit. See Hall, 621 A.2d at 850 & n. 3 (noting that right of contribution is an equitable remedy which arises among joint tortfeasors to promote fairness, by distributing plaintiff's losses equally among wrongdoers, and deterrence, by ensuring that all responsible parties share in cost of wrongdoing). However, as this court explained in Berg, “making particular credit rules contingent upon” whether a party is unjustly enriched "would only increase uncertainty and make it even more difficult for litigants to negotiate settlements.” 673 A.2d at 1257. Moreover, in this case the jury was not asked to determine whether GWU was negligent. GWU has not been exonerated; it merely settled to avoid the risk of litigation. By seeking contribution, however, GWU now concedes that it is a tortfeasor. Therefore, although GWU is not an adjudicated tortfea-sor, we have no basis to assume that it is inequitable for it to have paid $2,000,000 to Paul. Cf. Rose, 163 U.S.App.D.C. at 248, 501 F.2d at 808 (declining to sustain a pro tanto credit "in an amount exceeding the pro rata share of the verdict ascribable to the settling defendants,” who were found by the trial court not to be joint tortfeasors, because the nonsettling defendant — the only one negligent — would have been unjustly enriched).