This appeal concerning post-judgment interest under 28 U.S.C. § 1961 raises several esoteric issues. The principal question is whether interest should begin to run from the date of a district court judgment affirmed on appeal as to liability, but vacated and remanded for a new trial on damages, or only from the date of the second judgment. In the circumstances of this case, in which the more specifically instructed second jury awarded damages greater than those awarded in the first judgment, considerations of equity lead us to conclude that interest should run on the amount common to both district court judgments from the date of entry of the first judgment.
I.
Petitioner-appellant Bailey sued Chattem, Inc., a Chattanooga manufacturer, in a diversity action for breach of contract and fraud arising from a controversy over the defendant’s failure to commercialize and otherwise exploit a patented invention for improved paint developed by Bailey and assigned to Chattem. For further details, see Bailey v. Chattem, Inc., 684 F.2d 386 (6th Cir.1982). By stipulation of the parties, the case was tried before the Magistrate. The jury awarded $548,000 in compensatory damages and $75,000 in punitive damages for promissory fraud, and $27,000 in compensatory damages for failure to commercialize Bailey’s invention. The Magistrate on March 6, 1980 entered judgment in the total amount of $650,000. On October 27, 1980 the Magistrate amended the fraud judgment to $400,000 after conditioning denial of defendant’s motion for new trial on plaintiff’s acceptance of a $148,000 remittitur in the promissory fraud damages; the $75,000 punitive damages and $27,000 for failure to commercialize were left intact.
On appeal, a panel of this Court affirmed on liability and affirmed the $27,000 and $75,000 categories of damages. But the Court reversed the $400,000 in compensatory damages for fraud because, although it was “clear that Bailey was entitled to at least some compensatory damages, ... the trial court’s instructions on damages were wholly inadequate to guide the jury in the complicated task of weighing [the] evidence to find the amount by which Bailey was defrauded.” Id. at 394, 396-97 & n. 12 (emphasis in original).
On retrial, the jury awarded Bailey compensatory damages of $627,000 on the fraud claim. This judgment was entered by the Magistrate on August 5, 1983, and affirmed on appeal by this Court. Bailey v. Chattem, 779 F.2d 49 (6th Cir.1985), cert. denied, 475 U.S. 1065, 106 S.Ct. 1376, 89 L.Ed.2d 602 (1986).
On February 7, 1986 Bailey moved to amend the District Court’s judgment upon remand to provide that interest on the $627,000 award should run not from August 5,1983, the date of the judgment upon retrial, but from October 27, 1980.1 The *151Magistrate denied this motion, which forms the subject matter of this appeal.
II.
A preliminary question is whether Bailey has preserved the issue of post-judgment interest for appeal. Chattem argues that Bailey either should have moved this Court pursuant to Fed.R.App.P. 37 to amend its mandate in 1985 to provide for the interest he seeks, or should have made a post-trial motion in the District Court to amend its August 5,1983 judgment upon retrial. Because Bailey did neither, Chattem argues that Bailey is foreclosed from relief, citing as authority Briggs v. Pennsylvania Railroad Co., 334 U.S. 304, 68 S.Ct. 1039, 92 L.Ed. 1403 (1948), and Gele v. Wilson, 616 F.2d 146 (5th Cir.1980).
Briggs and Gele held that a district court has no authority on remand to calculate post-judgment interest from a date earlier than its post-remand entry of judgment unless the mandate of the court of appeals so directs. We do not agree, however, that either Briggs or Gele controls our power to modify the application of interest to a judgment. See Reaves v. Ole Man River Towing, Inc., 761 F.2d 1111 (5th Cir.1985) (distinguishing Briggs and Gele).
Bailey correctly notes that the August 3, 1982 mandate of this Court was appropriately silent on the subject of interest. That mandate did not order entry of a judgment for money damages but ordered a new trial. The issue of interest was not raised by the parties, and it is unreasonable to expect this court to deal with the interest issue in an opinion ordering a new trial.
The August 5, 1983 judgment of the District Court, which was affirmed by this Court in 1985, awarded Bailey $627,000 “with interest thereon at the rate provided by law.” It is proper for the Magistrate to determine, upon affirmance, what interest was “provided by law,” and it is proper for this Court to review that determination.
III.
There are three issues that must be disposed of to resolve the appropriate application of post-judgment interest in this case. First, in this diversity case, does state or federal law determine when post-judgment interest begins to accrue? Next, should 28 U.S.C. § 1961 be strictly construed to begin interest only from entry of a second judgment upon remand from a modification on appeal, or more liberally to provide interest from the date when a correct judgment should have been entered? Finally, how should the 1982 amendment of § 1961 affect the application of interest, when the original judgment was entered before that amendment and the judgment upon retrial was entered subsequent to the amendment? We consider these issues in order.
A.
Since the 1948 revision and at the time the original judgment in this case was rendered, the relevant post-judgment interest statute relied on the applicable state interest rate:
Interest shall be allowed on any money judgment in a civil case recovered in a district court____ Such interest shall be calculated from the date of the entry of the judgment, at the rate allowed by State law.
28 U.S.C. § 1961 (1976). Effective Oct. 1, 1982, the third sentence was amended to provide a uniform federal post-judgment interest rate, as follows:
Such interest shall be calculated from the date of the entry of the judgment, at a rate equal to the coupon issue yield equivalent (as determined by the Secretary of the Treasury) of the average accepted auction price for the last auction of fifty-two week United States Treasury bills settled immediately prior to the date of the judgment. The Director of the Administrative Office of the United States Courts shall distribute no*152tice of that rate and any changes in it to all Federal judges.
28 U.S.C. § 1961(a)(1982).
On the question of which judgment should be used to trigger interest in this case, we conclude that this is a matter of federal, not state, law. Differing views on the choice of law question have been expressed, however, see, e.g., Affiliated Capital Corp. v. City of Houston, 793 F.2d 706, 709 n. 3 (5th Cir.1986) (en banc) (federal court sitting in diversity must apply substantive law of the state regarding rate and accrual of interest on a judgment); Weitz Co. v. Mo-Kan Carpet, Inc., 723 F.2d 1382, 1387 (8th Cir.1983) (Swygert, Senior Judge, dissenting) (if Congress intended to declare the rate of interest due on judgments in diversity cases, it would have done so in more explicit terms than are contained in the statute as amended in 1982).
The amended statute by its terms covers interest “on any money judgment in a civil case recovered in a district court.” It is true that the Supreme Court in Klaxon Co. v. Stentor Electric Manufacturing Co., 313 U.S. 487, 61 S.Ct. 1020, 85 L.Ed. 1477 (1941), observed that in diversity cases “the courts of the state and the federal courts sitting within the state should be in harmony” on whether post-judgment interest should be allowed to run from verdicts as well as from judgments. Id. at 497, 61 S.Ct. at 1022 (quoting Massachusetts Benefit Association v. Miles, 137 U.S. 689, 691, 11 S.Ct. 234, 235, 34 L.Ed. 834 (1891)). Miles held that when state law allowed interest to accrue from a verdict before judgment, the predecessor statute to § 1961 — which also provided that interest be calculated from the “date of the judgment” — was not to the contrary because “where such allowance is expressly made by a state statute, we consider it a right given to a successful plaintiff, of which he ought not to be deprived by a removal of his case to the Federal court.” Miles, 137 U.S. at 691, 11 S.Ct. at 235.
Both Klaxon and Miles thus stand for the merely permissive proposition that a state law allowing post-judgment interest to accrue from a date earlier than court entry of the judgment should be respected in diversity cases.2 Moreover, Klaxon and Miles were decided before later elaboration of the Erie doctrine had taken place.
In Erie Railroad Co. v. Tompkins, 304 U.S. 64, 78, 58 S.Ct. 817, 822, 82 L.Ed. 1188 (1938), the Supreme Court held that “Congress has no power to declare substantive rules of common law applicable in a State. . . .” In Hanna v. Plumer, 380 U.S. 460, 85 S.Ct. 1136, 14 L.Ed.2d 8 (1965), the Court provided the clarification that when a federal rule and a state law conflict, the state law must give way so long as Congress has the constitutional power to regulate an area which is “rationally capable of classification as either” substantive or procedural. Id. at 472, 85 S.Ct. at 1144. While prejudgment interest is a substantive aspect of damages in a diversity case and is thus properly viewed as a matter of state law, post-judgment interest is at least “rationally capable of classification” for Erie purposes as procedural. Although the primary purpose of post-judgment interest is to compensate a successful plaintiff for the time between his entitlement to damages and the actual payment of those damages by the defendant, post-judgment interest also serves a salutary housekeeping purpose for the forum by creating an incentive for unsuccessful defendants to avoid frivolous appeals and by minimizing the necessity for court-supervised execution upon judgments. See Weitz, 723 F.2d at 1386-87; S.Rep. No. 275, 97th Cong., 2d Sess. 30, reprinted in 1982 U.S.Code Cong. & Admin.News 11, 40.
*153Our conclusion is buttressed by Justice Harlan’s concurrence in Hanna and by the most recent Supreme Court expression in this area. In Hanna, Justice Harlan expressed the view that state law should govern only the “primary stages of private activity” of the parties from which litigation may arise. 380 U.S. at 475-77, 85 S.Ct. at 1146-47 (Harlan, J., concurring). Accrual of post-judgment interest is hardly the type of “primary ... private activity” that would form the basis of business planning; nor does it seem likely that a somewhat more liberal rule in the federal courts would result in forum-shopping.
In Burlington Northern Railroad Co. v. Woods, — U.S. -, 107 S.Ct. 967, 94 L.Ed.2d 1 (1987), the Court held that a Hanna -type “conflict” existed between the federal standard for assessing penalties for frivolous appeals, a broad discretionary standard, and an Alabama statute that imposes a mandatory penalty upon judgments that are affirmed on appeal. See id. 107 S.Ct. at 971 & n. 5 (citing Fed.R.App.P. 37, 38; 28 U.S.C. § 1961). Woods clarifies Hanna by providing that state law must give way to the federal standard even though it is discretionary. The Woods rationale suggests that a federal rule should be applied here rather than applying a state rule under the Klaxon-Miles line of reasoning. Federal law therefore governs the question of which judgment should be used in determining the date when interest begins to run in this case. Accord, Weitz Co. v. Mo-Kan Carpet, Inc., 723 F.2d 1382 (8th Cir.1983) (majority opinion); G.M. Brod & Co v. U.S. Home Corp., 759 F.2d 1526, 1542 (11th Cir.1985).
B.
Chattem argues that interest can accrue only from the judgment entered after retrial because the earlier vacated judgment has become a nullity. This view is based on a formalistic reading of the statutory phrase “date of entry of the judgment” favored in the Second, Eighth,3 and Tenth Circuits but rejected in our own and four other circuits and at least impliedly disfavored by the Supreme Court. We agree with the majority view that the statutory phrase must be interpreted broadly to effectuate the purposes of post-judgment interest. See generally, Comment, Interest on Judgments in the Federal Courts, 64 Yale L.J. 1019 (1955) (hereinafter Interest on Judgments).
In National Bank v. Mechanics’ National Bank, 94 U.S. (4 Otto) 437, 24 L.Ed. 176 (1876), the Court allowed interest pursuant to the predecessor to § 1961 to accrue from a demand for payment which, although not reduced to judgment, was “proved to the satisfaction of the comptroller” and therefore was “of the same efficacy as judgments, ... occupied the same legal ground,” and hence was “within the equity, if not the letter, of these statutes.” Id. 94 U.S. (4 Otto) at 439.
This Circuit and the First, Third, Fifth, and Ninth Circuits have taken this “equity of the statute” approach to hold, in a proper case, that post-judgment interest can accrue from an event other than the final judgment entered by the district court. See, e.g., United States v. Bank of Celina, 823 F.2d 911 (6th Cir.1986) (district court modification of district court judgment without intervening appeal); Swartzbaugh Manufacturing Co. v. United States, 289 F.2d 81 (6th Cir.1961) (judgment reduced on appeal in Contract Appeals case not subject to § 1961); United States v. Michael Schiavone & Sons, Inc., 450 F.2d 875 (1st Cir.1971) (judgment reduced on appeal); Poleto v. Consolidated Rail Corp., 826 F.2d 1270 (3d Cir.1987) (verdict); Affiliated Capital Corp. v. City of Houston, 793 F.2d 706 (5th Cir.1986) (en banc) (interest available upon JNOV reversal, but rejected on equitable grounds); Louisiana & Arkansas Railway Co. v. Pratt, 142 F.2d 847 (5th Cir.1944) (appellate reversal of JNOV for defendant; interest accrued from the verdict for plaintiff “when & when the judgment should have been entered”); Turner v. Japan Lines, Ltd., 702 F.2d 752 (9th Cir.1983) (reversal of JNOV for defendant); *154Perkins v. Standard Oil Co. of California, 487 F.2d 672 (9th Cir.1973) (damages reduced on appeal); see generally Interest on Judgments at 1048 (“the real issue is who should bear the cost resulting from the loss of use of the money”).
Chattem argues that this entire line of cases can be distinguished because the amount of damages due Bailey never was ascertained until judgment upon retrial, citing dictum in Turner, 702 F.2d at 754-56, and case law from other circuits, including Ashland Oil, Inc. v. Phillips Petroleum Co., 607 F.2d 335 (10th Cir.1979), cert. denied, 446 U.S. 936, 100 S.Ct. 2153, 64 L.Ed.2d 788 (1980); Hysell v. Iowa Public Service Co., 559 F.2d 468 (8th Cir.1977); and Powers v. New York Central Railroad Co., 251 F.2d 813 (2d Cir.1958). These last three cases, while perhaps susceptible of an interpretation that they could have been decided on an “ascertainment” ground, in fact were grounded upon a per se rule that the § 1961 “judgment” must be the judgment upon remand. Compare Powers, 251 F.2d at 818 (“The delay in the entry of the proper judgment was necessary in the sense that time for appellate reviews was required.”) (quoting Chemical Bank & Trust Co. v. Prudence-Bonds Corp., 213 F.2d 443, 445 (2d Cir.), cert. denied, 348 U.S. 856, 75 S.Ct. 80, 99 L.Ed. 674 (1954)) with Powers, 251 F.2d at 818 (majority opinion “an ironbound, inequitable and illogical rule”) (Lumbard, J., dissenting); see Ashland Oil, 607 F.2d at 336; Hysell, 559 F.2d at 476-77.
The Ninth Circuit also has rejected the Turner “ascertainment” theory. In Handgards, Inc. v. Ethicon, Inc., 743 F.2d 1282 (9th Cir.1984), cert. denied, 469 U.S. 1190, 105 S.Ct. 963, 83 L.Ed.2d 968 (1985), post-judgment interest was permitted to accrue from the initial date of judgment after a jury verdict was vacated and remanded for a new trial to determine liability and damages under a different standard of liability. The second jury again found liability and awarded nearly double the amount of damages awarded originally. See id. at 1298-1300 (relying on Twin City Sportservice, Inc. v. Charles O. Finley & Co., 676 F.2d 1291, 1311 (9th Cir.), cert. denied, 459 U.S. 1009, 103 S.Ct. 364, 74 L.Ed.2d 400 (1982)).
Twin City viewed the award of interest in circumstances analogous to this case as mandatory, not discretionary. 676 F.2d at 1311. We would not go so far. See Affiliated Capital, 793 F.2d at 709-10.
Determining the “equity of the statute” in a case like this requires an inquiry into the nature of the initial judgment, the action of the appellate court, the subsequent events upon remand, and the relationship between the first judgment and the modified judgment. In this case, our Court’s affirmance of liability, coupled with our determination that “some damages” would be due upon retrial, makes it equitable to allow interest to accrue from the date of the first judgment upon remand. The retrial of the damages issue was tried upon the same theory of liability as before. Liability for damages had already been determined; what remained was the measurement of damages.
The plaintiff concedes that equity requires that interest should run only on the first $400,000 of the second judgment rather than the full $627,000. We therefore conclude that when the measurement of damages found by a second, properly instructed jury includes within it a lesser amount of damages which was also found by the jury in the first trial, considerations of equity lead us to run interest on that lesser amount from the date of the first judgment.
Chattem argues that running interest on that portion of the second judgment which was included in the first judgment creates a double-counting problem. Relying on the testimony of the plaintiff’s economic expert, Chattem asserts that the portion of the 1983 jury’s award attributable to past damages included a Consumer Price Index-based adjustment for the period from 1981 to 1983. Chattem argues that the time value of the 1980 damages award was thus taken into account in the 1983 award. To also allow interest to accrue on that award will therefore result in the payment of interest on an award which has already been adjusted to compensate for the passage of *155time. This argument ignores the underlying rationale for the testimony of the plaintiff’s expert. The expert adjusted the values for each year in accordance with the CPI because the contract was tied to the CPI. Each year, Bailey was to be paid $32,400 in 1975 dollars (minus an offset for consulting). Therefore, the adjustments made by Bailey’s expert did not take into account the time value of the wages already due under the contract. He merely calculated the amount that was actually due each year. The same process was used to determine future earnings. The future earnings were brought back to present value, but the past earnings were not adjusted upward to reflect their 1983 value.
If the 1980 jury had calculated future earnings on the basis of CPI projections, their results for the period between 1981 and 1983 might have been different than those of the 1983 jury, since the later jury could rely on actual data rather than projections. Depending on the discrepancy between the projections and the actual data, this could result in either a windfall or a shortfall for Bailey. However, it is impossible to determine the amount of this windfall, if such a windfall was created. We will not engage in second-guessing a jury when doing so would require us to speculate as to the figures relied upon in jury deliberations.
Therefore, as long as the entire amount of the $400,000 1980 judgment was included within the 1983 judgment, interest on the $400,000 should run from 1980. In other words, interest should run on the entire amount of the 1980 judgment unless the 1980 value of the 1983 judgment is less than $400,000. For the 1980 value of the 1983 judgment to be that small, a discount rate of over 16% would have to be applied. While we cannot determine what discount rate would have been used in 1980 to determine the present value of that portion of the earnings stream which was attributable to the period between 1981 and 1983, it is clear that no reasonable jury would have relied on a discount rate as large as 16%. It is therefore safe to say that the entire 1980 award was included within the 1983 award, and that therefore interest on the $400,000 attributable to the 1980 award should run from 1980.
C.
The final issue is what rate of interest to apply. The first judgment was entered more than two years before the effective date of the 1982 amendment to § 1961. Courts have disagreed over whether to apply the federal method of determining interest to judgments entered before October 1, 1982. A majority of circuits have concluded that the amended statute should apply only to judgments entered after its effective date. See Campbell v. United States, 809 F.2d 563, 569 (9th Cir.1987) (collecting cases). But see R.W.T. v. Dalton, 712 F.2d 1225, 1234-35 (8th Cir.) (holding that the amended statute should apply to a pre-effective date judgment for the entire post-judgment period), cert. denied, 464 U.S. 1009, 104 S.Ct. 527, 78 L.Ed.2d 710 (1983).
The issue is whether “to apply the law in effect at the time [a court] renders its decision, unless doing so would result in manifest injustice or there is statutory direction or legislative history to the contrary.” Bradley v. School Board, 416 U.S. 696, 711, 94 S.Ct. 2006, 2016, 40 L.Ed.2d 476 (1974).
The Court in Campbell undertook a comprehensive review of the case law and sparse legislative history in this area, which we will not reiterate here. See Campbell, 809 F.2d at 568-76. We agree with the Ninth Circuit that what little legislative history exists on the 1982 amendments indicates that Congress did not intend the new method of computing interest to apply to judgments entered before the act’s effective date — at least for interest accruing before the effective date. We also agree that it is not unjust to impose interest at the Treasury bill rate after the act’s effective date. See id. at 574.
IY.
Accordingly, the order of the Magistrate is reversed and remanded for calculation of *156post-judgment interest consistent with this opinion. The calculation of interest should use the applicable state rates from October 27,1980 to October 1, 1982. From October 1, 1982, the effective date of the amendment to § 1961, to the 1983 judgment date and thereafter the calculation should use the applicable § 1961 rates.
. Bailey did not seek to have the interest calculated from the original judgment date of March 6, 1980, although the parties had agreed that interest on the two categories of damages affirmed by this Court in its 1982 decision should run from this date rather than the later October 27, 1980 date of the amended judgment of the District Court. Amendment to Judgment on Mandate, Dec. 9, 1982, App. 55.
Because Bailey does not seek to invoke the March 6, 1980 date as the date from which interest on the $627,000 should run, we shall *151treat October 27, 1980 as the original date of entry of judgment and thus not reach the question whether this date should be related back to March 6, 1980.
. Bailey asserts in his brief that both Tennessee and California law, which provide the forum and underlying substantive law that governs the fraud claim in this case, would permit accrual of post-judgment interest from the first judgment. See Bailey v. Chattem, Inc., 684 F.2d at 392-93; American Buildings Co. v. DBH Attachments, Inc., 676 S.W.2d 558 (Tenn.App.1984); Stockton Theatres, Inc. v. Palermo, 55 Cal.2d 439, 11 Cal.Rptr. 580, 360 P.2d 76 (1961); Snapp v. State Farm Fire & Casualty Co., 60 Cal.2d 816, 36 Cal.Rptr. 612, 388 P.2d 884 (1964). In view of our determination infra that federal, not state law, governs the question of accrual of post-judgment interest, we express no opinion on the result reached applying state law.
. A recent Eighth Circuit case, however, without reference to the earlier case law, appears to adopt a contrary view. See Buck v. Burton, 768 F.2d 285 (8th Cir.1985).