Calculate statutory pre-judgment interest across all 50 U.S. jurisdictions. Model partial payments, generate court-ready amortization schedules, and export to CSV — built for paralegals, boutique firms, and corporate counsel.
No payments recorded. Add payments to model a full amortization schedule.
| # | Start | End | Days | Balance | Interest | Payment | Cumul. Int. |
|---|---|---|---|---|---|---|---|
| Run calculation to view schedule | |||||||
Pre-judgment interest compensates a prevailing party for the time value of money lost while a dispute was pending. Unlike post-judgment interest (which begins after entry of judgment), pre-judgment interest runs from a legally defined accrual date — typically the date of breach, the date of loss, or the date a demand was made — through the date the court enters its judgment.
In commercial disputes, pre-judgment interest is frequently the second-largest line item after actual damages. On a $500,000 claim in Massachusetts (12% simple), a three-year litigation timeline adds $180,000 in pre-judgment interest before any attorney fees or punitive damages are considered. This is not an afterthought — it is a material part of every commercial case's economic exposure.
The single most consequential variable in a pre-judgment interest calculation is the start date. The rules differ by state and by claim type:
For simple interest (the dominant approach in U.S. pre-judgment law):
When partial payments are present, interest accrues on the outstanding balance for each period. A $50,000 payment on a $250,000 claim at 8% per year reduces the interest-bearing balance to $200,000 going forward — the previously accrued interest is not forgiven, it is already calculated and accumulated.
The schedule generated by this tool breaks the interest period into monthly segments. Each row shows the opening balance, the number of days in that period, the interest that accrued, any payment applied, and the closing balance. The cumulative interest column shows total interest earned through that date — this is the figure you would cite in a damages calculation.
Payment rows are highlighted in gold. When a payment is entered, the balance decreases in that period's "Ending Balance" column, and all subsequent interest calculations reflect the reduced principal. This mirrors the standard commercial damages model used in litigation support.
Rates are subject to legislative change. Several states (FL, TX, GA) use floating rates tied to the prime rate or a state-set index. Verify current rates before submitting calculations to court.
Pre-judgment interest uses the formula: Interest = Principal × Annual Rate × (Days / 365) for simple interest, which is the standard for most U.S. jurisdictions. The principal is the face value of the claim, the annual rate is the statutory rate for that jurisdiction, and days is the number of calendar days from the accrual date through the judgment date. This tool calculates day counts precisely from the dates you enter and applies the full schedule with any partial payments you add.
The accrual start date depends on the jurisdiction and claim type. For breach of contract, most states begin on the date of the breach. For tort claims, many begin on the date of injury or the filing date. Some states require a formal demand letter before interest can run. Federal diversity cases use the substantive law of the applicable state to determine the pre-judgment accrual date. This is the highest-risk input in any pre-judgment interest calculation — consult with counsel to confirm the correct start date before submitting to court.
Most states authorize pre-judgment interest in commercial and contract disputes by statute. The rates range from 4% (Kansas) to 12% (Massachusetts, Rhode Island, South Dakota, Washington). A few states limit pre-judgment interest to specific claim types or require court approval. Tort claims face more restrictions — many states prohibit or limit pre-judgment interest in personal injury cases. For commercial contract disputes between businesses, pre-judgment interest is almost universally available and often mandatory upon prevailing.
Partial payments reduce the outstanding principal on which interest accrues going forward. Interest that has already accumulated remains part of the damages claim. For example: on a $250,000 principal at 8% per year, a $50,000 payment after 12 months reduces the balance to $200,000. Year 1 interest = $20,000 (on $250K). Year 2 interest = $16,000 (on $200K). Total interest = $36,000. Total judgment = $200,000 + $36,000 = $236,000. Use this tool's partial payments feature to model these scenarios precisely.
Simple interest accrues only on the original principal. Compound interest accrues on both principal and previously accumulated interest — creating exponential growth over time. Nearly all U.S. jurisdictions use simple interest for statutory pre-judgment calculations. Compound pre-judgment interest requires explicit statutory authorization or a contractual compound interest provision. For long-running litigation, the difference is material: at 10% for 5 years, simple interest yields 50% of principal; daily compounding yields approximately 64.9% of principal. Use compound only when the underlying contract or statute specifically provides for it.
When a contract specifies an interest rate, that rate generally controls over the statutory default, provided it does not exceed the state's usury limit. If the contract is silent on interest, the governing jurisdiction's statutory pre-judgment rate applies. If the contract contains a choice-of-law clause designating a specific state, that state's statutory rate applies in the absence of a specified contractual rate. Use this tool's manual rate override to enter any contractual rate — simply type it into the Annual Interest Rate field after selecting your jurisdiction.
Click the "Export CSV" button in the output panel after running a calculation. The exported file includes a header block with jurisdiction, rate, method, and principal; the full month-by-month amortization schedule with all columns; and a summary section with total interest, outstanding principal, and total judgment amount. Open the CSV in Excel, apply table formatting, and it is ready for use as a litigation support exhibit. Always include counsel's verification and a citation to the applicable statute when submitting interest schedules to court.
Federal post-judgment interest under 28 U.S.C. § 1961 is set weekly based on the 1-year Treasury constant maturity rate — it is a floating rate, not a fixed statutory rate. This tool uses an approximate current rate; verify the exact weekly rate at the U.S. District Court's website or the Federal Reserve's published T-bill rate before using it in a federal case. For federal diversity cases, pre-judgment interest is typically governed by the applicable state's law, not § 1961, which is a post-judgment statute. Select the substantive state law jurisdiction for pre-judgment calculations in diversity actions.
White Oak Intelligence provides litigation support modeling for commercial disputes: lost profits analyses, economic damages models, present value calculations, and expert-level financial reconstruction. We build the numbers that hold up to opposing expert scrutiny — not estimates, but documented, defensible financial models backed by actual data.
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