Choosing the right interest tool for United States (Federal)

When you’re dealing with federal cases, “interest” is rarely just one number. You may have:

• Different time periods (pre‑judgment vs. post‑judgment)
• Different interest bases (federal statute vs. contract rate)
• Different compounding rules (simple vs. compound, annual vs. monthly)
• Different principal buckets (fees, costs, sanctions, partial payments)

A generic percentage calculator won’t cut it. This guide walks through how to choose the right DocketMath interest workflow for United States (Federal) matters, and what inputs you should be thinking about for each.

Choose the right tool

Start with a basic question:

What exactly are you trying to calculate interest on, and under what authority?

Most federal workflows fall into one of these buckets:

1. Federal post‑judgment interest under 28 U.S.C. § 1961
2. Pre‑judgment interest (often governed by state law or contract)
3. Contractual or agreed interest (promissory notes, settlement agreements, etc.)
4. Mixed interest (federal + contract, or multiple buckets)
5. Audit and reconciliation (checking someone else’s math)

DocketMath’s interest calculator can handle each of these, but the inputs and setup change depending on your scenario.

1. Federal post‑judgment interest (28 U.S.C. § 1961)

This is the most common federal use case: interest accruing on a money judgment entered in a U.S. district court.

Typical scenario

• You have a judgment date and judgment amount
• You need interest from the judgment date until:

  • Payment, or
  • A later date (e.g., for a motion or updated status)
• You’re applying the federal rate under 28 U.S.C. § 1961, based on the weekly average 1‑year Treasury yield.

How to set up in DocketMath

In the interest calculator:

1. Jurisdiction

   • Select: United States (Federal) (US‑FED)
2. Interest type / basis

   • Choose: Post‑judgment interest (28 U.S.C. § 1961) or the equivalent federal post‑judgment option.
3. Principal amount

   • Enter the money judgment amount (excluding costs or fees you plan to treat separately).
4. Start date

   • Use the date of entry of judgment.
5. End date

   • Use:

     • The payment date, if fully paid, or
     • A calculation‑through date (e.g., “through 01/31/2026”) if you’re updating an outstanding judgment.
6. Compounding rules

   • Federal post‑judgment interest is typically compounded annually under § 1961(b).
   • Select the annual compounding option if it isn’t auto‑selected.

DocketMath will:

• Pull the correct weekly Treasury rate for the judgment week
• Apply it from the judgment date through your end date
• Handle annual compounding automatically

When to use a more advanced setup

Use a more detailed workflow if:

• You have partial payments at different dates
• You have fees or costs added after judgment (e.g., attorney’s fees awarded post‑judgment)
• The court modified or amended the judgment (e.g., remittitur, additur, or amended judgment date)

In DocketMath, look for options like:

• “Add payment” (with date and amount)
• “Add new principal component” (e.g., fees added later)
• “Treat this as a new judgment date” (if the court clearly resets interest from an amended judgment)

2. Pre‑judgment interest in federal cases

Pre‑judgment interest in federal litigation is trickier because:

• Sometimes it’s governed by state law (e.g., in diversity cases)
• Sometimes it’s governed by federal law (e.g., certain federal claims)
• Sometimes it’s governed by contract (specified rate, compounding, and accrual rules)

From a calculation perspective, you need to know:

• Start date: When does interest begin?
• End date: Usually the date of judgment (or a different date if ordered)
• Rate: Fixed percentage, variable, statutory, or contract rate?
• Compounding: Simple, annual, monthly, daily?

How to set up in DocketMath

Use the interest calculator in a custom or statutory pre‑judgment mode:

1. Jurisdiction

   • Choose United States (Federal) if you’re modeling pre‑judgment interest in a federal case, but:

     • If you’re applying a state statutory pre‑judgment rate, you may instead select the relevant state jurisdiction (e.g., California, New York) if available.
2. Interest type / basis

   • Choose: Custom pre‑judgment interest or a specific state/federal pre‑judgment option, depending on what you’re applying.
3. Principal amount

   • Use:

     • The damages amount for which pre‑judgment interest was awarded, or
     • A series of amounts if damages accrued over time (e.g., invoices, missed payments).
4. Rate and compounding

   • Enter the exact rate (e.g., 9% simple, 10% annual compounding).
   • If using a statutory rate tied to something like the prime rate, confirm how that rate changes over time and set up multiple periods if needed.
5. Dates

   • Start date: As specified by the statute, contract, or court order (e.g., date of breach, date of loss, mid‑point of damages).
   • End date: Usually the judgment date, unless the court specifies a different cutoff.

If pre‑judgment interest is awarded on multiple tranches (e.g., invoices over a year), you can:

• Add each invoice or loss as a separate principal entry with its own start date
• Apply the same rate across all, or different rates if required

DocketMath then aggregates:

• Interest per tranche
• Total pre‑judgment interest
• Combined principal + interest through the judgment date

3. Contractual or agreed interest (federal cases with contracts)

Many federal cases are contract disputes or settlements with contractual interest that doesn’t track federal statutes.

Examples:

• Promissory note with “12% per annum, compounded monthly”
• Settlement agreement: “6% simple interest from 30 days after execution until payment”
• Loan agreement pegged to “prime + 3%” with quarterly compounding

Here, the contract is your roadmap. The calculator’s job is to:

• Mirror the contract’s rate
• Mirror the compounding frequency
• Respect start and end dates, and any default or step‑up clauses

How to set up in DocketMath

1. Jurisdiction

   • Choose United States (Federal) if your matter is in federal court, but you’re applying a contract rate.
2. Interest type / basis

   • Choose: Custom interest / contract rate.
3. Principal

   • Use the principal balance that actually bears interest under the contract.
4. Rate

   • Enter:

     • A fixed rate (e.g., 8% per year), or
     • Multiple rates over time if the contract says the rate changes (e.g., default rate after a certain date).
5. Compounding

   • Select the compounding frequency specified in the contract:

     • Simple (no compounding)
     • Annual
     • Semi‑annual
     • Quarterly
     • Monthly
     • Daily
6. Dates and events

   • Start date: As per contract (e.g., funding date, default date, 30 days after invoice).
   • End date: Payment date, or a calculation‑through date.
   • Add payments with dates to reduce principal and recalculate interest from each payment date.

4. Mixed interest: federal + contract or multiple buckets

Many real‑world matters aren’t cleanly “just federal” or “just contract.” Common mixed scenarios:

• Contract damages with contract interest up to judgment, then federal post‑judgment interest after judgment
• A judgment that includes:

  • Principal damages
  • Pre‑judgment interest
  • Attorney’s fees
  • Costs
  • Sanctions
    and you need to know which of those components bear post‑judgment interest

In DocketMath, think in layers.

Step 1: Pre‑judgment layer

Use a custom or statutory pre‑judgment workflow to:

• Calculate interest on contract damages through the judgment date, or
• Calculate state/federal pre‑judgment interest as appropriate

Capture as outputs:

• Pre‑judgment interest total
• Principal + pre‑jud

Next steps

Run the Interest calculator now and save the inputs alongside the result so the workflow is repeatable. You can start directly in DocketMath: Open the calculator.

Capture the source for each input so another team member can verify the same result quickly.

Related reading

• Interest rule lens: Maine

• Choosing the right deadlines tool for Canada

• Common interest mistakes in Rhode Island

• Why we started the DocketMath blog