The issue here is how to determine the point in time at which a plaintiff has suffered “actual injury” from *594professional malpractice for purposes of applying a statute of limitations under which the limitations period does not commence until the plaintiff has sustained actual injury. This is the third time in the past two years that the court has addressed this question. (See International Engine Parts, Inc. v. Feddersen & Co. (1995) 9 Cal.4th 606 [38 Cal.Rptr.2d 150, 888 P.2d 1279]; ITT Small Business Finance Corp. v. Niles (1994) 9 Cal.4th 245 [36 Cal.Rptr.2d 552, 885 P.2d 965].) In the two previous cases, a majority of the court attempted to formulate “bright line” rules to define the circumstances under which a plaintiff had suffered actual injury. I dissented in each case (ITT Small Business Finance Corp. v. Niles, supra, at p. 258 (dis. opn. of Kennard, J.); International Engine Parts, Inc. v. Feddersen & Co., supra, at p. 623 (conc. & dis. opn. of Kennard, J.)), pointing out that the “bright lines” the majority was attempting to draw were ultimately impractical and that the question of when a plaintiff has suffered actual injury is necessarily a question of fact to be decided on a case-by-case basis.
Today, a majority of the court recognizes that the actual injury determination is a question of fact. I concur fully in this conclusion and in the judgment. I write separately to emphasize that this court’s decision in Budd v. Nixen (1971) 6 Cal.3d 195 [98 Cal.Rptr. 849, 491 P.2d 433] provides the proper analytical framework for making the “actual injury” determination in all attorney malpractice cases, and also to clarify one point (the significance of the expiration of a limitations period on a third party claim) on which I find the lead opinion’s discussion somewhat confusing.
I
By statute, an action against an attorney for professional malpractice must be commenced within one year after the plaintiff knew or should have known of the attorney’s wrongful act or omission, or within four years after the date of the act or omission, whichever occurs first. (Code Civ. Proc., § 340.6, subd. (a).) The statute further provides, however, that the time to commence the attorney malpractice action is tolled during the period in which the “plaintiff has not sustained actual injury.” (Id., § 340.6, subd. (a)(1), italics added.) At issue in this case, and in two other cases that have recently come before this court (Laird v. Blacker (1992) 2 Cal.4th 606 [7 Cal.Rptr.2d 550, 828 P.2d 691]; ITT Small Business Finance Corp. v. Niles, supra, 9 Cal.4th 245), is the meaning of the term “actual injury” as used in this statute.
When the Legislature enacted the statute of limitations for attorney malpractice actions (Code Civ. Proc., § 340.6), it codified this court’s decisions in Neel v. Magana, Olney, Levy, Cathcart & Gelfand (1971) 6 Cal.3d 176 [98 *595Cal.Rptr. 837, 491 P.2d 421] [holding that the limitations period for an attorney malpractice claim does not begin to run until the plaintiff knew or should have known of the attorney’s wrongful act or omission] and Budd v. Nixen, supra, 6 Cal.3d 195 [holding that the limitations period for an attorney malpractice claim does not begin to run until the plaintiff has suffered appreciable and actual harm]. (Laird v. Blacker, supra, 2 Cal.4th 606, 611.) For this reason, the decision in Budd v. Nixen is the controlling authority on the meaning of “actual injury” in this context. (See ITT Small Business Finance Corp. v. Niles, supra, 9 Cal.4th 245, 259 (dis. opn. of Kennard, J.).)1
Justice Arabian’s lead opinion reaffirms four propositions taken directly from the language and reasoning of Budd v. Nixen, supra, 6 Cal.3d 195:
(1) Determining when a plaintiff in a legal malpractice case has sustained actual injury is predominantly a factual rather than a legal determination. (Lead opn., ante, at pp. 585-586; Budd v. Nixen, supra, 6 Cal.3d at p. 202.)
(2) The determination of actual injury does not depend upon or require a prior adjudication, judgment, or settlement. (Lead opn., ante, at pp. 591-592; Budd v. Nixen, supra, 6 Cal.3d at pp. 197-204.)
(3) An injury is not “actual” if it causes only nominal damages, speculative harm, or the threat of future harm. (Lead opn., ante, at p. 589; Budd v. Nixen, supra, 6 Cal.3d at p. 200.)
(4) It is the fact of injury and not the amount of injury that is the relevant consideration. (Lead opn., ante, at p. 589; Budd v. Nixen, supra, 6 Cal.3d at p. 201.)
The first two propositions—that the “actual injury” determination is predominantly factual and that it does not necessarily depend upon the timing or outcome of a prior adjudication, judgment, or settlement with a third party— formed the basis of my dissenting opinions in ITT Small Business Finance *596Corp. v. Niles, supra, 9 Cal.4th 245, 258 (dis. opn. of Kennard, J.) and in International Engine Parts, Inc. v. Feddersen & Co., supra, 9 Cal.4th 606, 623 (conc. & dis. opn. of Kennard, J.). My concurrence provides the fourth vote to form the majority in this case, thereby giving these propositions, once again, the force of law. (See Cal. Const., art. VI, § 2.)
Another theme of my dissents was that the factual issues posed by the “actual injury” determination may not be eliminated or converted into legal issues by the promulgation of “bright line” rules, a proposition that the lead opinion also accepts. (Lead opn., ante, at p. 591, fn. 4.)
The lead opinion affirms two additional propositions that are relevant in determining when “actual injury” occurs in so-called “missed statute” cases—that is, cases in which a client claims that his or her attorney committed malpractice either by failing to commence an action for the client against a third party within the time required by the applicable statute of limitations or by misadvising the client about that requirement. The lead opinion affirms that in these “missed statute” cases (1) actual injury is not established by the mere expiration of the limitations period on the client’s claim against the third party (lead opn., ante, at p. 591, fn. 4), and (2) determining actual injury may require resolution of factual issues such as which limitation period applies to the third party claim and whether the third party waived or would be estopped to assert a defense based on expiration of the limitations period (id. at p. 591). I agree with both of these propositions, which are also, by my concurrence, given the force of law. As I explain, however, I find the lead opinion confusing in its discussion of their application in “missed statute” cases.
II
The lead opinion recognizes, correctly, that in the “missed statute” cases “actual injury” is not established by the mere expiration of the limitations period on the client’s claim against the third party. But it does so only in a footnote (lead opn., ante, at p. 591, fn. 4), and only by disapproving Finlayson v. Sanbrook (1992) 10 Cal.App.4th 1436 [13 Cal.Rptr.2d 406] to the extent it implies the- “bright line” rule that in “missed statute” cases, “actual injury” occurs upon expiration of the limitations period for the third party claim. Elsewhere, the lead opinion might be read as suggesting that expiration of the limitations period for the third party claim, without more, could constitute “actual injury.” (Lead opn., ante, at pp. 589-590, 593.) I concur in the lead opinion only with the understanding that it does not in fact conclude or hold that the mere expiration of a conventional limitations period constitutes “actual injury.”
*597As this court recognized in Budd v. Nixen, supra, 6 Cal.3d 195, 200, a negligent act by an attorney is not actionable if it results only in speculative harm or the possibility of future harm. In the “missed statute” cases, the harms most often at issue are the loss of the client’s claim against the third party and increased legal expenses incurred to determine the effect of the missed statute or to enforce or attempt to enforce the third party claim. But the mere expiration of the limitations period on the third party claim does not extinguish that claim. Although the expiration of the limitations period may result in increased litigation costs, those costs become “actual injury” only when they are incurred. These points deserve some elaboration.
Because in civil actions the statute of limitations is a law of procedure, it affects only the remedy, not the substantive right or obligation. (Nelson v. Flintkote Co. (1985) 172 Cal.App.3d 121, 733 [218 Cal.Rptr. 562]; 3 Witkin, Cal. Procedure (3d ed. 1985) Actions, § 308, p. 337; id., § 314, p. 345.) In other words, a cause of action is not extinguished or impaired by the mere passage of time, and the maintenance of the claim is not precluded simply by the running of the statutory period. (Nelson v. Flintkote Co., supra, at pp. 731-732.) The statute of limitations is an affirmative defense that is forfeited if not appropriately invoked by the defendant. (See, e.g., Minton v. Cavaney (1961) 56 Cal.2d 576, 581 [15 Cal.Rptr. 641, 364 P.2d 473]; 5 Witkin, op. cit. supra, Pleading, § 1039, pp. 453-455.) Thus, unless the defendant properly invokes the statute of limitations as a defense, the expiration of the statutory period does not affect even the remedy. Because the expiration of a limitations period by itself does not extinguish a claimant’s right or bar the remedy, it cannot constitute “actual injury” to the claimant.
As the lead opinion correctly recognizes (lead opn., ante, at p. 589), “actual injury” may consist of an impairment or diminution, as well as the total loss or extinction, of a right or remedy. (E.g., Davies v. Krasna (1975) 14 Cal.3d 502 [121 Cal.Rptr. 705, 535 P.2d 1161, 79 A.L.R.3d 807] [disclosure destroyed marketability of story]; Hensley v. Caietti (1993) 13 Cal.App.4th 1165 [16 Cal.Rptr.2d 837] [legal relations and rights altered and obligation created by contract]; Sirott v. Latís (1992) 6 Cal.App.4th 923 [8 Cal.Rptr.2d 206] [judgment resulting in irreversible loss of right to insurance]; Ruchti v. Goldfein (1980) 113 Cal.App.3d 928 [170 Cal.Rptr. 375] [judgment terminating pension rights]; Walker v. Pacific Indemnity Co. (1960) 183 Cal.App.2d 513 [6 Cal.Rptr. 924] [judgment in excess of insurance coverage]; Jensen v. Sprigg (1927) 84 Cal.App. 519 [258 P. 683] [claim discharged in bankruptcy]; United States v. Gutterman (9th Cir. 1983) 701 F.2d 104 [tax penalty assessment].) But each of these cases involved a present and unconditional impairment, diminution, or loss of a legal right or interest. In contrast, expiration of a limitation period results in no present *598impairment of the claim, but only the threat of future loss contingent on another party’s willingness and ability to assert the statute of limitations as a defense.
To be sure, some rights are expressly conditioned on their assertion within a specified period of time, and these rights may indeed be extinguished by failure to assert them within the allowed time. (See Williams v. Pacific Mutual Life Ins. Co. (1986) 186 Cal.App.3d 941, 949 [231 Cal.Rptr. 234]; 3 Witkin, op. cit. supra, Actions, § 315, p. 345.) But ordinary civil statutes of limitation do not operate in this manner, and that is all we are concerned with here.
The lead opinion refers to Basinger v. Sullivan (Ind.Ct.App. 1989) 540 N.E.2d 91 and to Woodburn v. Turley (5th Cir. 1980) 625 F.2d 589. (Lead opn., ante, at pp. 589, 590.) But neither case involves California law or our principle of “actual injury.” Equally unhelpful for present purposes are the lead opinion’s references to Campbell v. Magana (1960) 184 Cal.App.2d 751 [8 Cal.Rptr. 32] (concluding that the “loss” of the “nuisance value” of an unmeritorious lawsuit was not damage) and Marshall v. Packard-Bell Co. (1951) 106 Cal.App.2d 770 [236 P.2d 201] (holding that an allegation of duress did not toll a statute of limitations).
The lead opinion also observes that the Restatement Second of Torts, in section 7, subdivision (1), defines “injury” as the invasion of any legally protected interest. (Lead opn, ante, at pp. 589-590.) But the lead opinion neglects to mention that, in subdivision (2) of the same section, the Restatement defines “harm” as loss or detriment in fact. A comment to the section observes that the difference between “injury” and “harm” under the Restatement is the difference between a legal wrong (which may cause no physical or monetary detriment) and actual damage. (Rest.2d Torts, § 7, com. a, p. 13.) Thus, “actual injury” as used in our attorney malpractice statute of limitations is more akin to “harm” than to “injury” as those terms are defined in the Restatement.
In the “missed statute” cases, therefore, expiration of the statute of limitations, without more, does not constitute “actual harm.” This does not mean, however, that a client cannot bring a malpractice action against an attorney for a “missed statute” unless and until the third party has successfully asserted a defense based on the statute of limitations. It does mean, however, that if the client did not file suit on the third party claim, the “actual injury” determination may require resolution of factual issues such as whether filing suit against the third party would have been futile or otherwise imprudent and, if so, when that futility became established; and *599whether the client incurred any attorney fees or other expenses to determine the futility of pursuing the third party action and, if so, when the expenses were incurred. In determining whether pursuing the third party claim would have been futile or imprudent, factual issues that may arise include which statute of limitations applied to the third party claim, whether the third party may have waived a defense based on the statute of limitations, and whether the third party was or may have been estopped to assert a defense based on the statute of limitations. Determination of issues of waiver and estoppel often depend upon the resolution of factual questions. (Platt Pacific, Inc. v. Andelson (1993) 6 Cal.4th 307, 319 [24 Cal.Rptr.2d 597, 862 P.2d 158].) And which statute of limitations applies in a case may well turn on resolution of such factual issues as whether the obligation was founded upon an instrument in writing. (Benard v. Walkup (1969) 272 Cal.App.2d 595, 600-603 [77 Cal.Rptr. 544].)
Conclusion
As I have long maintained, in construing the term “actual injury” in the attorney malpractice statute of limitations (Code Civ. Proc., § 340.6), there is no better guide than this court’s opinion in Budd v. Nixen, supra, 6 Cal.3d 195, which teaches that determining the point of actual injury requires a close analysis of the facts of the particular case and is not amenable to resolution by simplistic “bright line” rules. A majority of this court now adopts this view and applies it to the “missed statute” category of attorney malpractice actions. Accordingly, I concur in the lead opinion, although with the understanding that in a “missed statute” case the mere expiration of a conventional limitations period is not actual injury.
When it codified the decision in Budd v. Nixen, supra, 6 Cal.3d 195, the Legislature provided that the one-year and four-year limitations periods would be tolled until the attorney’s malpractice had resulted in “actual injury.” In Budd, however, this court made no reference to tolling, instead treating the occurrence of “actual and appreciable harm” simply as an element necessary to the accrual of the cause of action for attorney malpractice, and thus necessary also to the commencement of the limitations period. The lead opinion asserts that this difference in approach limits the “instructional value” of Budd v. Nixen. (Lead opn., ante, at p. 589, fn. 2.) I disagree. So far as I can discern, the difference in approach has no practical significance. There is no reason in law or logic why it should limit the value or authority of this court’s decision in Budd v. Nixen in construing the statute that codifies it.