How to use the prejudgment interest calculator
There is no single national interest rate for a debt that is paid late in the United States. A written contract rate controls first. Without one, state law supplies a statutory rate, and the figures differ widely: New York uses nine percent under N.Y. C.P.L.R. 5004, California applies ten percent to contract obligations under Cal. Civ. Code 3289, and other states sit well below both. Enter the rate that governs your agreement or your state.
Once a federal judgment is entered, the rate changes. 28 U.S.C. 1961 sets post-judgment interest at the weekly average one-year constant maturity Treasury yield for the week before judgment, compounded annually, which is usually far lower than a contract rate.
Every state also caps what a lender may charge. Usury limits vary by state, by the type of lender and by whether the borrower is a business, and a rate above the cap can make the excess unenforceable or expose the lender to penalties. The optional cap field flags that for you. This tool uses simple interest on a 365 or 360 day year as of September 2026. This calculator is for reference only and is not legal advice. Consult a licensed attorney about your specific situation.
Frequently asked questions
A valid contract rate normally governs. If the agreement is silent, courts apply the prejudgment interest rate set by the state whose law controls the claim.
Yes, but on a federal judgment it runs at the Treasury-based rate in 28 U.S.C. 1961 rather than the contract rate, unless the parties agreed otherwise and the court approves.