Worked example: interest in United States (Federal)

This walkthrough shows how an interest calculation for a federal money judgment in the United States might look in DocketMath’s Interest calculator for jurisdiction US‑FED.

The goal is not to give legal advice or say what must be done in any particular case. Instead, this is a worked numerical example so you can see:

• What typical inputs look like
• How the calculation flows
• How the result changes when you tweak assumptions

For your own matters, always confirm which statute, rule, and rate apply before using any numbers in practice.

Example inputs

We’ll use a federal civil money judgment scenario where post‑judgment interest is governed by 28 U.S.C. § 1961, which ties the rate to the weekly average 1‑year constant maturity Treasury yield published by the Federal Reserve.

To keep this example concrete, we’ll fix a specific judgment date and assume a published rate for that week. (In a real calculation, you’d pull the actual rate in effect on the judgment date.)

You can experiment with the same structure directly in the live calculator at /tools/interest.

Scenario overview

• Case: Federal civil action resulting in a money judgment
• Judgment principal: $500,000.00
• Judgment date: June 3, 2024
• Interest type: Post‑judgment interest (US Federal, 28 U.S.C. § 1961)
• Compounding: Annual (per statute)
• Interest accrues: From June 3, 2024 through December 31, 2025
• Payment: No payments made during the period (all principal outstanding)

Interest rate assumption (for illustration)

For this worked example, we’ll assume:

• Applicable 1‑year Treasury yield for the calendar week ending just before June 3, 2024: 4.80%
• Statutory rate: 4.80% per year, simple rate, compounded annually

How these inputs look in DocketMath

In DocketMath’s Interest calculator for US‑FED, the inputs for this example would be conceptually like:

• Jurisdiction: United States – Federal (US‑FED)
• Calculation type: Post‑judgment interest
• Principal: 500,000.00
• Interest rate source: Fixed rate (user‑specified)
• Annual rate: 4.80%
• Compounding: Annually
• Start date: 2024‑06‑03
• End date: 2025‑12‑31
• Day‑count convention: Actual/365 (typical for statutory post‑judgment interest; always verify)

You can run the same structure directly in the live calculator at /tools/interest.

Example run

We’ll compute total post‑judgment interest on $500,000 from June 3, 2024 to December 31, 2025 at 4.80%, compounded annually, using an Actual/365 day‑count.

Run the Interest calculator using the example inputs above. Review the breakdown for intermediate steps (segments, adjustments, or rate changes) so you can see how each input moves the output. Save the result for reference and compare it to your actual scenario.

Step 1: Break the period into interest “segments”

Because we’re compounding annually and our period spans more than one year, it’s useful to separate:

1. From 2024‑06‑03 to 2024‑12‑31 (first partial year)
2. From 2025‑01‑01 to 2025‑12‑31 (second full year)

DocketMath handles this automatically, but we’ll show the math explicitly.

Step 2: Count days in each segment

Using Actual/365:

1. 2024‑06‑03 to 2024‑12‑31

   • June 3 through December 31, 2024
   • Days in segment: 212 days (for illustration; DocketMath will compute the exact count)

2. 2025‑01‑01 to 2025‑12‑31

   • Entire calendar year 2025
   • Days in segment: 365 days

Step 3: Compute interest for the first segment (2024‑06‑03 to 2024‑12‑31)

Inputs:

• Principal: $500,000.00
• Annual rate: 4.80% (0.048 as a decimal)
• Day‑count: Actual/365
• Days: 212

Formula for simple interest over a partial year with Actual/365:

[ \text{Interest} = \text{Principal} \times \text{Rate} \times \frac{\text{Days}}{365} ]

Plug in the numbers:

1. Fraction of year:

[ \frac{212}{365} \approx 0.58082 ]

1. Annual interest on $500,000 at 4.80%:

[ 500{,}000 \times 0.048 = 24{,}000 ]

1. Interest for 212 days:

[ 24{,}000 \times 0.58082 \approx 13{,}939.68 ]

So:

• Interest for 2024 segment ≈ $13,939.68
• New balance at 2024‑12‑31 (after annual compounding):

[ 500{,}000.00 + 13{,}939.68 = 513{,}939.68 ]

This becomes the starting principal for 2025 because we’re compounding annually.

Step 4: Compute interest for the second segment (2025‑01‑01 to 2025‑12‑31)

Now we run the same formula for a full year on the updated principal.

Inputs:

• Principal: $513,939.68
• Annual rate: 4.80%
• Day‑count: Actual/365
• Days: 365

Fraction of year:

[ \frac{365}{365} = 1 ]

Interest:

[ 513{,}939.68 \times 0.048 \approx 24{,}669.10 ]

So:

• Interest for 2025 segment ≈ $24,669.10
• Balance at 2025‑12‑31:

[ 513{,}939.68 + 24{,}669.10 \approx 538{,}608.78 ]

Step 5: Summarize the result

At December 31, 2025, given our assumptions:

• Original principal: $500,000.00
• Total interest accrued:

[ 13{,}939.68 + 24{,}669.10 \approx 38{,}608.78 ]

• Total amount owed (principal + interest): ≈ $538,608.78

DocketMath would present something like:

You can generate and export the full Explain++ breakdown (with dates, day counts, and formulas) directly from /tools/interest for your own fact pattern.

Sensitivity check

A single interest calculation is rarely the end of the story. Lawyers, analysts, and courts often need to know how the number changes when:

• The rate is different
• The dates shift
• The compounding method is changed
• There are partial payments along the way

here are a few simple “what‑if” checks using the same base scenario.

1. What if the rate were 3.00% instead of 4.80%?

Keep all assumptions the same except the annual rate.

• Principal: $500,000.00
• Start date: 2024‑06‑03
• End date: 2025‑12‑31
• Rate: 3.00%
• Compounding: Annually
• Day‑count: Actual/365

repeat the same steps:

1. 2024 segment (212 days at 3.00%)
2. 2025 full year at 3.00% on the updated principal

DocketMath will instantly recompute, but conceptually:

• Annual interest on $500,000 at 3% = $15,000
• 2024 fraction (212/365 ≈ 0.58082) → ≈ $8,712.30
• New principal at 2024‑12‑31 ≈ $508,712.30
• 2025 interest at 3% on that amount ≈ $15,261.37
• Total interest

Related reading

• Worked example: deadlines in New York

• Interest rule lens: Maine

• Common interest mistakes in Rhode Island

• Why we started the DocketMath blog