Post Judgment Calculator: How Interest Is Computed

A post-judgment calculator works out the interest that accrues on a court judgment from the date it was entered until the date it is paid. You enter the judgment amount, the statutory interest rate, and the start and end dates, and it returns the total interest owed plus the full amount due. This guide explains how the math works, where the rate comes from, and what to watch out for when using one.

Formula

The core formula for simple post-judgment interest is:

Interest = Principal × (Annual Rate ÷ 100) × (Days Elapsed ÷ 365)

Where:

• Principal (p) – the judgment amount in dollars, including any pre-judgment interest or costs if the court order says so.
• Annual Rate (r) – the statutory post-judgment interest rate, expressed as a percentage per year.
• Days Elapsed (de – ds) – the number of days between the judgment date and the payment date.
• 365 – the number of days used in the standard year for interest calculations.

This is simple interest, not compound interest. The interest does not earn interest of its own unless a statute or the judgment specifically says otherwise, which is rare. The result is the total interest owed on top of the original judgment amount.

Worked Example

Using the default values from the calculator above:

• Principal: $10,000
• Annual rate: 8%
• Start date: January 15, 2024
• End date: January 15, 2025

First, count the days between the two dates. From January 15, 2024 to January 15, 2025 is exactly 365 days (2024 is a leap year, but the period spans February 29, 2024, making it 366 days from Jan 15, 2024 to Jan 15, 2025 – however, the calculator uses the standard 365-day year for the divisor, so the day count is 366). Wait – let us be precise: the calculator computes the difference in days as 366 because 2024 is a leap year. So:

Interest = $10,000 × (8 ÷ 100) × (366 ÷ 365)

Interest = $10,000 × 0.08 × 1.0027397

Interest = $10,000 × 0.0802192

Interest = $802.19 (rounded to two decimals)

Total due = $10,000 + $802.19 = $10,802.19

If the period were exactly one non-leap year (365 days), the interest would be $800.00 and the total $10,800.00. The leap day adds $2.19.

Where the Interest Rate Comes From

Post-judgment interest rates are set by statute, not by the court or the parties. In U.S. federal courts, the rate is tied to the weekly average one-year constant maturity Treasury yield, published by the Federal Reserve, plus a statutory add-on (currently 3 percentage points under 28 U.S.C. § 1961). State courts have their own schedules – some use a fixed rate (e.g., 6% or 9%), others peg it to a published index like the prime rate or the state treasury bill rate, and some adjust annually or semi-annually.

The rate that applies is the one in effect on the date the judgment is entered, and it generally stays fixed for the life of that judgment. If the judgment is from a federal court, the rate is set on the judgment date and does not change. If a state court, check the specific state statute – some states change the rate every year, which means a multi-year judgment could have different rates for different periods. A good calculator will let you enter a single rate; for variable-rate judgments, you may need to compute each segment separately and add them together.

How to Use the Calculator Correctly

To get an accurate figure, you need three things:

• The exact judgment amount – look at the final order or judgment document. This may include attorney fees, costs, and pre-judgment interest if the court awarded them. Do not include amounts that were later paid or credited unless you adjust the principal accordingly.
• The correct statutory rate – verify this with the court clerk, your attorney, or the state judicial branch website. Using last year’s rate when the rate changed will give a wrong answer.
• Accurate dates – the start date is the date the judgment was entered on the docket, not the date of the verdict or the date the judge signed it. The end date is the date payment is actually received, not the date a check was mailed. If the debtor pays in installments, you must recalculate interest on the declining balance.

Once you have these, the calculation is straightforward. The result tells you the minimum amount the debtor owes. If the judgment includes a contractual interest rate (for example, a breach of contract case where the agreement specified 12% interest), that rate may supersede the statutory rate. Always read the judgment language carefully.

Common Mistakes and Misconceptions

Several errors routinely appear when people compute post-judgment interest by hand:

• Using 360 days instead of 365 – some bank-style calculations use a 360-day year, but most post-judgment statutes specify a 365-day year (or actual days). Using 360 inflates the interest by about 1.4%.
• Counting the start date – interest typically begins on the day after the judgment is entered, not on the judgment date itself. Many statutes say “from the date of entry,â€� which courts interpret as the day after. Check your jurisdiction.
• Forgetting about partial payments – if the debtor pays $5,000 halfway through the period, the interest for the second half should be computed on the remaining $5,000. A simple calculator that only takes one principal amount will overstate the interest.
• Compounding by mistake – post-judgment interest is almost always simple interest. Do not compound it annually unless the statute or judgment explicitly says so.
• Ignoring the rate change date – in states with annual rate adjustments, a judgment entered in 2023 may accrue at 7% for 2023 and 8% for 2024. You must split the calculation at the change date.

Limits of the Simple Calculation

This calculator assumes a single, unchanging principal amount and a single, unchanging rate over the entire period. Real judgments often deviate from these assumptions:

• Partial payments – each payment reduces the principal, so interest must be recomputed on the remaining balance from the payment date forward.
• Variable statutory rates – some states change the rate annually. You would need to run the calculation separately for each rate period and sum the results.
• Compound interest provisions – certain contracts or statutes (rare but possible) require annual compounding. This calculator does not handle that; you would need a compound interest formula instead.
• Appeals and stays – if the judgment is appealed and a stay of execution is granted, interest may or may not continue to accrue depending on the rules. Some states stop interest during an appeal; others do not.
• Currency and foreign judgments – if the judgment is in a foreign currency, the exchange rate on the payment date may affect the amount owed in local currency.

For any of these situations, the calculator gives you a starting point, not the final answer. When significant money is at stake, confirm the arithmetic with the court clerk or an attorney who can verify the applicable rate and the exact day-count rule for your jurisdiction.

How to Verify Your Result

If you want to double-check the calculator’s output, you can do a quick manual check:

1. Count the exact number of days between the start and end dates using an online day counter or a calendar.
2. Divide the annual rate by 100 to get the decimal rate (e.g., 8% → 0.08).
3. Multiply the principal by the decimal rate, then by the day count, then divide by 365.
4. Add the result to the principal for the total due.

For example, with $10,000 at 8% for 365 days: 10000 × 0.08 × 365 ÷ 365 = $800.00. The total is $10,800.00. If your manual calculation matches the calculator, you can trust the result. If it differs, check whether you used the correct day count or whether a leap day is involved.

Frequently Asked Questions

Does post-judgment interest compound?
No, not in the vast majority of cases. Federal law (28 U.S.C. § 1961) and most state statutes provide for simple interest only. The interest is calculated on the principal judgment amount and does not itself earn interest. Only if the underlying contract or a specific statute says “compound� should you use compounding.

What is the current federal post-judgment interest rate?
The federal rate is the weekly average one-year constant maturity Treasury yield plus 3 percentage points, set on the date the judgment is entered. It changes weekly, so there is no single “current� rate – you must look up the rate for the specific week your judgment was entered. The U.S. Courts website publishes the rates.

Can I use this calculator for pre-judgment interest?
No. Pre-judgment interest is governed by different rules – it may run from the date of injury or breach, may use a different rate (often the state’s legal rate), and may be discretionary with the judge or jury. This calculator is only for the post-judgment period.

What if the debtor pays in installments?
You must recalculate after each payment. Interest accrues on the unpaid principal balance only. For example, if you have a $10,000 judgment at 8% and the debtor pays $4,000 after 100 days, you compute interest on $10,000 for 100 days, then on $6,000 for the remaining days. This calculator does not handle partial payments; you would run it multiple times or use a spreadsheet.

Does interest stop if the debtor appeals?
It depends on the jurisdiction and whether a stay of execution is granted. In federal court, interest continues to accrue during an appeal unless the judgment is reversed or modified. Some states stop interest while an appeal is pending if the appellant posts a bond. Check your local rules or ask the court clerk.

Is the judgment amount including costs and attorney fees?
Only if the judgment document says so. Some judgments award “costs� separately, and interest may not run on those until they are taxed (fixed) by the court. Read the judgment carefully. If it says “plaintiff recovers $10,000 plus costs,� the interest typically runs only on the $10,000 until the costs are added to the judgment.

Related

• How to Calculate Run Time
• How to Calculate Precipitation
• How to Calculate Precipitation Rate

in p | Principal judgment amount | $ | 10000 | 0 | 100000000
in r | Annual interest rate | % | 8 | 0 | 100
in ds | Start date (judgment entered) | - | 2024-01-15 | 2020-01-01 | 2030-12-31
in de | End date (payment date) | - | 2025-01-15 | 2020-01-01 | 2030-12-31
out interest | Interest owed | $ | p * (r/100) * (de - ds) / 365 | 2
out total | Total due | $ | p + p * (r/100) * (de - ds) / 365 | 2