Legal Interest Calculator: Calculate Pre- and Post-Judgment Interest

When you win a lawsuit, the judgment amount isn't always the end of the math. Interest accrues from key dates — sometimes from the date of the injury, sometimes from the date of filing, and almost always from the date of judgment until payment. Getting this calculation right can add thousands of dollars to what you're actually owed. The CalcHub Legal Interest Calculator handles both pre- and post-judgment interest using the applicable statutory rates.

Two Types of Legal Interest

Pre-judgment interest: Interest that accrues from the date the damage occurred (or from the date of filing, depending on the state) until the date judgment is entered. Some states allow it; some don't; some allow it only for liquidated (easily calculable) damages. Post-judgment interest: Interest that accrues on the judgment amount from the date judgment is entered until the judgment is paid. This is broadly available in all jurisdictions.

Statutory Interest Rates

Jurisdiction	Pre-Judgment Rate	Post-Judgment Rate
Federal courts	N/A (usually)	1-year Treasury bill rate (set weekly)
California	7% simple	10% simple
New York	9% simple	9% simple
Texas	5% (contract)	Prime rate + 1%
Florida	Treasury rate	Treasury rate + 4.75%
Illinois	5%	9%

Rates vary widely and some states use floating rates tied to Treasury yields. The calculator uses current published rates for each state.

Calculating Post-Judgment Interest

Simple interest formula: Principal × Rate × Time (years)

A $75,000 judgment in California at 10% per year:

• After 6 months: $75,000 × 10% × 0.5 = $3,750


• After 1 year: $75,000 × 10% × 1.0 = $7,500


• After 2 years: $75,000 × 10% × 2.0 = $15,000

So a defendant who delays payment by 2 years owes $90,000 total — a meaningful incentive to collect promptly.

Compound vs. Simple Interest

Most states use simple interest on judgments. Federal judgments also use simple interest. However, some contractual interest provisions and some states use compound interest, which grows faster:

Interest Type	$50,000 principal at 9%	After 3 years
Simple	$50,000 + ($50,000 × 9% × 3)	$63,500
Compounded annually	$50,000 × (1.09)³	$64,772

The calculator handles both and clearly states which method applies to your jurisdiction and claim type.

Pre-Judgment Interest Example

A contract dispute in New York where plaintiff wasn't paid $25,000 on a contract due January 1, 2023. Judgment entered March 15, 2026 (3.21 years later):

• Pre-judgment interest: $25,000 × 9% × 3.21 years = $7,222.50
• Total judgment amount: $25,000 + $7,222.50 = $32,222.50
• Post-judgment interest then accrues on $32,222.50 until paid

Does post-judgment interest automatically compound?

It depends on the state. Most states apply simple interest on the original judgment only. Some apply interest on the total (principal + accrued interest). The calculator notes which rule applies for your state.

What if the defendant is partially paying down a judgment over time?

The calculator handles partial payments. Enter each payment date and amount, and it applies payments first to accrued interest and then to principal (the standard rule), recalculating the running balance.

Can I collect interest on attorney's fees awarded in a judgment?

Generally yes — an award of attorney's fees becomes part of the judgment and accrues post-judgment interest from the date of the judgment order.

Related Calculators

• Settlement Calculator — Factor accrued interest into settlement negotiations
• Billing Hours Calculator — Calculate total attorney fees to include in the judgment
• Court Fee Calculator — Add filing costs to your total claim