About the Judgment Interest Calculator
This judgment interest calculator works out how much interest has accrued on a court judgment or legal claim between two dates. Enter the principal amount, the annual interest rate that applies, the start and end dates and the compounding method, and you get the interest owed, the total due and the per diem — the amount of interest that accrues each day.
It is useful for creditors and debtors checking a payoff figure, attorneys preparing a writ or satisfaction of judgment, and anyone estimating pre-judgment interest on a contract claim. The rate and compounding depend on the court: most US states set a statutory post-judgment rate (often simple interest, e.g. 9% or 10%), while federal post-judgment interest under 28 U.S.C. § 1961 uses the weekly average 1-year Treasury yield for the week before judgment, computed daily and compounded annually.
Choose simple interest for most state judgments and annual compounding for federal judgments. Days are counted exactly between the dates on a 365-day year. The calculator does not apply partial payments; if payments were made, run it for each period on the reduced balance.
With the default inputs, the interest owed is $3,384.25. Change any value above to recalculate instantly.
How to use the judgment interest calculator
- 1Enter the judgment or claim amount.
- 2Enter the interest rate set by statute or the court.
- 3Pick the date interest starts and the date you want to calculate through.
- 4Choose simple interest or the compounding method your jurisdiction uses.
- 5Use the total and per diem for a payoff letter or satisfaction of judgment.
Formula and method
Days are counted exactly between the start and end dates. Simple interest multiplies the principal by the annual rate and by the fraction of a year elapsed; interest never earns interest. This is how most state post-judgment statutes work.
For annual compounding (used for federal judgments under 28 U.S.C. § 1961), interest is computed daily and added to the balance on each anniversary: y full years grow at (1 + r) each, then the remaining d′ days accrue simple interest. Monthly and daily options compound at r/12 and r/365. The per diem is the principal times the rate divided by 365.
- P
- Judgment principal
- r
- Annual interest rate (decimal)
- d
- Days between start and end dates
- y, d′
- Whole years and leftover days
Worked examples
$25,000 state judgment at 9% simple interest
From March 1, 2025 to September 1, 2026 is 549 days. Simple interest is $25,000 × 9% × 549 ÷ 365 = $3,384.25, so $28,384.25 is due. Each additional day adds about $6.16.
Federal judgment at 4.25% compounded annually
The 1,310 days contain three full years and 215 extra days. The balance grows to $80,000 × 1.0425³ for the whole years, then accrues simple interest for the remaining 215 days, for about $12,909 of interest.
$12,500 at 10% compounded daily for two years
The period is 731 days because 2024 is a leap year. Compounding daily at 10% ÷ 365 gives $12,500 × (1 + 0.1/365)^731 ≈ $15,271.30, or about $2,771 of interest — more than the $2,503 simple interest would give.
Frequently asked questions
How is post-judgment interest calculated?+
Most states apply a fixed statutory rate as simple interest on the unpaid judgment from the date it is entered until it is paid. Multiply the principal by the rate and by the number of days divided by 365. Some states use a variable rate tied to market rates each year.
What is the federal post-judgment interest rate?+
Under 28 U.S.C. § 1961, it equals the weekly average 1-year constant maturity Treasury yield for the calendar week before the judgment date, as published by the Federal Reserve. Interest is computed daily and compounded annually until paid.
What is pre-judgment interest?+
Pre-judgment interest compensates a plaintiff for the time between the loss (or the date a debt became due) and the judgment. Whether it is allowed, and at what rate, depends on state law, the type of claim and any contract terms.
What is a per diem on a judgment?+
The per diem is the amount of interest that accrues each day, usually calculated as the principal multiplied by the annual rate and divided by 365. It is used to update a payoff amount to the exact day of payment.
How do partial payments affect judgment interest?+
Payments are usually applied first to accrued interest and then to principal. After a payment, interest continues on the remaining principal. To model this, calculate each period separately using the reduced principal from the payment date.
Results are general estimates and not legal advice. Laws vary by jurisdiction — consult a qualified attorney.