MO Rev Stat § 408.020 (2021)
2021 Missouri Revised Statutes|Title XXVI - Trade and Commerce|Chapter 408 - Legal Tender and Interest|Section 408.020 - When no rate of interest is agreed upon, nine percent allowed as legal interest.

Effective - 28 Aug 1979   408.020. When no rate of interest is agreed upon, nine percent allowed as legal interest. — Creditors shall be allowed to receive interest at the rate of nine percent per annum, when no other rate is agreed upon, for all moneys after they become due and payable, on written contracts, and on accounts after they become due and demand of payment is made; for money recovered for the use of another, and retained without the owner's knowledge of the receipt, and for all other money due or to become due for the forbearance of payment whereof an express promise to pay interest has been made. ­­-------- (RSMo 1939 § 3226, A.L. 1979 S.B. 305)  Prior revisions: 1929 § 2839; 1919 § 6491; 1909 § 7179  (1952) Where assignee of life insurance policies paid premiums thereon, but did not surrender same for their cash value so as to cause them to become due and payable, they became due and payable upon the death of insured, so that interest or right to reimbursement for premiums under this statute did not accrue prior to such death. Boyle v. Crimm, 363 Mo. 731, 253 S.W.2d 149. (1955) Demand for real estate broker's commission is unnecessary to start running of interest where such commission becomes due under contract. Doerflinger Realty Co. v. Fields (A.), 281 S.W.2d 609. (1958) In absence of demand for payment of unwritten account, the filing of suit substitutes therefor and the interest bearing period starts as of the date of the verdict. The verdict need not separately state the amount of interest allowed and error in amount allowed may be cured by remittitur. Weekley v. Wallace (A.), 314 S.W.2d 256. (1960) Where water district bonds contained no provision for the payment of interest after maturity, the statutory interest rate applied after demand was made. State ex rel. Stern Bros. & Co. v. Stilley (Mo.), 337 S.W.2d 934.  (1961) Where laborer filed a claim against contractor on his bond but the evidence did not show that he ever made a demand for payment against the principal in the bond, the bonding company would not be liable for any interest until such time as demand was made and therefore in this case the allowance of interest was improper. Phoenix Assurance Co. of New York v. Appleton City, 296 F.2d 787. (1962) In action to recover balance due on subcontract for covering subgrade with topsoil, the fact that parties honestly disagreed as to amount of fill provided under subcontract did not make the sum due thereunder unascertainable and court did not err in allowing interest thereon from date of acceptance of the work. Eastmount Const. Co. v. Transport Mfg. & Equip. Co., 301 F.2d 34. (1964) A promissory note which provides when the indebtedness evidenced thereby becomes due and payable is a written agreement within the meaning of this section and a demand of payment is not necessary to start the accrual of interest under the statute. Sebree v. Rosen (Mo.), 374 S.W.2d 132. (1966) Court did not err in directing jury to award interest if they found for plaintiff, instead of only permitting it to do so. Schultz v. Queen Insurance Co. (A.), 399 S.W.2d 230. 1974) Held that amount due was readily ascertainable and interest from original demand was part of measure of damages even though the sum originally demanded was far in excess of the sum finally stipulated as owing. Slay Warehousing Co., Inc. v. Reliance Insurance Co. (C.A. Mo.), 489 F.2d 214. (1985) Issue of prejudgment interest and all the facts necessary for an award must appear in the petitions. Folk v. Countryside Casualty Co. (Mo. App. E.D.), 686 S.W.2d 882. (1986) Prejudgment interest is not available for breach of a contract where damages are based upon lost profits. Universal Power Systems v. Godfather Pizza, 818 F.2d 667 (8th Cir.). (1987) Where amount of debt was disputed and where one party claimed that other party was estopped from claiming true debt, amount was not liquidated or readily ascertainable by reference to recognized legal standards as required by this section. Total Petroleum, Inc. v. Davis, 822 F.2d 734 (8th Cir.) (2003) Insured's claim for uninsured motorist benefits is unliquidated and not subject to prejudgment interest. McKinney v. State Farm Mutual Insurance, 123 S.W.3d 242 (Mo.App.W.D.).