This case is before the Court for the second time. As a result of the first appeal the Court remanded the case for a redetermination of damages. See Slay Warehousing Co. v. Reliance Insurance Co., 471 F.2d 1364 (8th Cir. 1973). Upon remand the parties entered into a stipulation as to the amount of damages due appellant. Left to the trial court under the stipulation was the question of prejudgment interest. Slay Warehousing contended that it was entitled to interest computed from July 1, 1965, the date of its demand for certain payments pursuant to the insurance contract between the parties. The trial court denied the request for interest and appellant has brought that denial before this Court for review.

Missouri law governs the issue and the relevant statute reads as follows:

Creditors shall be allowed to receive interest at the rate of six per cent per annum, * * * for all moneys after they become due and payable, on written contracts.

Mo.Rev.Stat. 408.020 (1949). The Supreme Court of Missouri consistently has held the statute requires an award of prejudgment interest where the amount due is readily ascertainable though not strictly liquidated. See Denton Construction Co. v. Missouri State Highway Commission, 454 S.W.2d 44, 59-60 (Mo.1970); Laughlin v. Boatmen's National Bank, 354 Mo. 467, 189 S.W.2d 974, 979-980 (1945). In addition, the Missouri Court has recognized that prejudgment interest on a readily ascertainable sum is not in the nature of a penalty, but is a part of the measure of damages.1 Indeed, the award of prejudgment interest in a case in which Section 408.020 is applicable is not a matter of court discretion; it is compelled. See Denton Construction Co., supra, 454 S.W.2d at 60.

Thus the issue for this Court becomes whether the amount due under the insurance contract was readily ascertainable. On July 1, 1965 plaintiff made demand upon defendant for a sum representing an amount expended in salvage operations, initiated in an attempt to mitigate damages that resulted from an accident covered undee the defendant's policy. Although the sum demanded was far in excess of the sum finally stipulated as owing, the supporting statements that accompanied the July 1, 1965 demand provided a basis to ascertain the amount owed appellants; therefore, the statute applies and prejudgment interest must be paid from the date of demand. See United States Fidelity & Guaranty Co. v. Empire State Bank, 448 F.2d 360, 368-369 (8th Cir. 1971); American Insurance Co. v. First National Bank, 409 F.2d 1387, 1392 (8th Cir. 1969); Eastmount Construction Co. v. Transport Manufacturing & Equipment Co., 301 F.2d 34, 42-43 (8th Cir. 1962). Accordingly, we reverse and remand for entry of judgment in accordance with this opinion.

Reversed and remanded.