Prejudgment Interest on Damages Calculator

Prejudgment interest compensates plaintiffs for the time value of money — damages incurred years before the verdict have lost purchasing power and opportunity cost. Rates and rules vary dramatically by state. California uses 7-10% depending on damage type. New York uses 9% commercial / 6% general. Florida uses 10% (adjusted quarterly). Texas uses 5-12%. On a $500,000 verdict 3 years post-injury at 9% simple, prejudgment interest adds $135,000.

When Interest Starts Accruing

States split on accrual start date. Injury date rule: interest runs from the moment damages were sustained (most personal-injury cases). Liquidation date rule: interest runs only from the date damages became precisely calculable (most contract cases). Demand date rule: interest runs from when plaintiff first formally demanded payment. New York uses different rules for different claim types. California allows prejudgment interest from injury date on personal injury verdicts under CCP 3291 once an offer-of-judgment process is followed. Always check state law because the difference between accrual rules can be $50K-$500K on serious cases.

Which Damages Qualify

Some states (Texas, Illinois) allow prejudgment interest on the full verdict including pain and suffering. Others (New York, California) limit interest to liquidated economic damages only — past medical bills and lost wages but not future damages or non-economic damages. Federal courts use 28 USC 1961 post-judgment but borrow state law for prejudgment. Some federal civil rights claims have specific provisions (FCRA, ERISA, ADEA) creating uniform prejudgment interest rules. Calculation method also matters: simple vs annual compounding vs daily compounding can change the result 20-40% on long-duration cases.

Last updated May 2026. Sources: U.S. Courts — Federal Judiciary.