Inputs you need for interest in United States (Federal)

Calculating federal interest sounds simple—“principal × rate × time”—until you’re staring at multiple payments, partial satisfactions, and a moving federal post‑judgment rate.

This guide walks through the exact inputs you’ll need to run an interest calculation for United States (Federal) in DocketMath’s interest calculator, how to find them, and how each input changes the output.

Use this as a checklist before you open the tool so you can get from “I think I know the numbers” to a documented, reproducible calculation.

Inputs you will need

For United States (Federal) interest calculations in DocketMath, you’ll typically need:

Use this checklist to gather the core inputs before you run the Interest tool.

• principal or judgment amount
• interest type (pre- or post-judgment)
• rate and compounding method
• start date and end/as-of date
• payments or credits that reduce principal
• day-count convention

1. Jurisdiction and interest type

• Jurisdiction: United States (Federal) (code: US-FED)
• Interest type:

  • Pre‑judgment interest
  • Post‑judgment interest
  • Both (if your matter spans before and after judgment)

How this affects the output:

• Pre‑judgment interest: Often depends on a rate specified by statute, contract, or court order.
• Post‑judgment interest (28 U.S.C. § 1961): Tied to a federal rate that changes over time, usually based on Treasury yields. The calculator will apply the correct rate for the period you specify, when it’s configured to do so.

2. Principal amounts (what the interest is applied to)

• Principal amount(s):

  • Single lump-sum judgment amount, or
  • Multiple line items (e.g., damages, fees, costs) if you want them tracked separately
• Currency (usually USD)

How this affects the output:

• The principal is the base that interest accrues on.
• If you break out components (e.g., “Damages,” “Attorney’s fees,” “Taxable costs”), DocketMath can:

  • Show interest per component, and
  • Help you document why totals look the way they do.

Examples:

• Simple case:

  • Principal: $100,000 (single judgment amount)
• More detailed case:

  • Damages: $80,000
  • Attorney’s fees: $15,000
  • Costs: $5,000

3. Relevant dates

For federal interest, dates are often the most sensitive input.

You’ll usually need:

• Start date for interest

  • Pre‑judgment: the date from which interest begins (e.g., date of loss, breach, or filing, if applicable)
  • Post‑judgment: the date of entry of judgment on the civil docket
• End date for interest

  • A specific cutoff date (e.g., “through 12/31/2025”), or
  • The date of payment / satisfaction
• Dates of partial payments or credits (if any)

  • Each payment date
  • Amount paid

How this affects the output:

• Shifting rates over time: For US‑FED post‑judgment interest, the applicable rate can change depending on the judgment date and any subsequent periods defined by statute or rule. DocketMath uses your dates to:

  • Pull the correct rate(s) for each period, and
  • Allocate interest day‑by‑day or period‑by‑period.
• Partial payments:

  • Reduce the principal (or total balance) as of the payment date.
  • Future interest is computed on the reduced balance, not the original principal.

4. Interest rate inputs

Depending on the type of interest and how your matter is structured, you may need:

• Federal post‑judgment rate source:

  • Typically, DocketMath will derive the rate for US‑FED from the correct Treasury yield and date. You usually don’t need to type the percentage manually if the jurisdiction is set correctly.
• Contractual or statutory pre‑judgment rate (if applicable):

  • A fixed annual percentage (e.g., “6% per annum”)
  • Or a variable rate formula (e.g., “Prime + 2%”) that you may need to convert to concrete numbers for the tool
• Any court‑ordered modifications:

  • For example, an order that sets:

    • A different rate than the default statute,
    • A specific compounding schedule, or
    • A different start date for interest.

How this affects the output:

• Higher rates produce non‑linear increases over time, especially when combined with compounding.
• If DocketMath is configured to auto‑lookup the federal rate, you’ll get:

  • Consistent rate selection across matters, and
  • A clear record of which rate was used and why.

5. Compounding and calculation conventions

Federal post‑judgment interest under 28 U.S.C. § 1961 is typically compounded annually, but you may encounter other conventions in your documents or orders.

For the calculator, you may need:

• Compounding frequency:

  • None (simple interest)
  • Annual
  • Monthly
  • Daily
• Day‑count convention (if the calculator exposes it for advanced control):

  • Actual/365
  • Actual/360
  • Actual/Actual

How this affects the output:

• Compounding frequency:

  • More frequent compounding → more interest over longer periods.
• Day‑count convention:

  • Changes how many “interest days” are counted in a year.
  • Over many years or large principals, this can materially affect totals.

If you’re replicating a court’s or expert’s numbers, matching these conventions is often the key to closing small gaps between your calculation and theirs.

6. Payment application rules

When there are multiple payments, you may need to decide how payments are applied:

• Payment allocation order:

  • Interest first, then principal, or
  • Principal first, then interest, or
  • A custom allocation (e.g., fees, then costs, then principal)
• Whether fees and costs accrue interest:

  • Some orders allow interest on fees/costs; others don’t.

How this affects the output:

• The same payment history can produce different remaining balances depending on whether payments:

  • Knock out interest first (common in many financial contexts), or
  • Go directly to principal.
• If fees and costs also bear interest, the total can be significantly higher compared to principal‑only interest.

Where to find each input

Here’s a practical checklist of where these numbers usually live in a federal matter.

Run it

Once you’ve gathered your inputs:

1. Open the interest tool
   Go to the DocketMath interest calculator: /tools/interest.

2. Select jurisdiction and interest type

   • Jurisdiction: United States (Federal) (US-FED)
   • Interest type: pre‑judgment, post‑judgment, or both, depending on your matter.

3. Enter principal and structure

   • Input each principal amount.
   • Optionally label components (e.g., “Damages,” “Fees,” “Costs”) for better reporting.

4. Set dates

   • Enter:

     • Start date(s) for interest.
     • End date or “as of” date.
   • Add each partial payment with:

     • Payment date
     • Payment amount
     • Allocation rules (if the tool allows per‑payment overrides).

5. Configure rates and compounding

   • Confirm the federal post‑judgment rate is being pulled automatically for US‑FED.
   • If there’s a contractual or court‑ordered rate, enter it explicitly.
   • Set compounding frequency and day‑count, matching your authority or document.

6. Review the breakdown

   • Use DocketMath’s step‑by‑step explanations (Explain++) to:

     • See interest by period,
     • Confirm which rate applied when, and
     • Reconcile against any existing calculations

Related reading

• Interest rule lens: Maine

• Inputs you need for deadlines in Australia

• Common interest mistakes in Rhode Island

• Why we started the DocketMath blog