How is prejudgment interest calculated?

In the states covered here it is simple interest on the principal from the date interest begins accruing (the date of loss, breach, or demand, depending on the claim) to the date judgment is entered: principal × annual rate × days ÷ 365. It applies only where the claim qualifies — generally a liquidated or readily ascertainable amount.

Why are only some states in this calculator?

A calculator is only honest where the rate is fixed by statute and the compounding rule is deterministic (simple interest, or fixed-rate annual compounding as in Colorado). States with a formula rate that changed over the accrual period, and states where prejudgment interest is discretionary, are excluded — computing a single number for those would mislead. Each has its own page explaining the method.

Prejudgment interest calculator

Interest on a liquidated claim from the date it began accruing to the date of judgment, at each state's fixed statutory rate — verified against the statute and cited on its own page. Covers the 19 states and D.C. where the rate is fixed (simple interest, plus Colorado's annual compounding), so the arithmetic is exact.

Read this first. Prejudgment interest is not automatic. This calculator does the arithmetic; it does not decide the two things that actually govern an award:

Whether it applies. Most of these states allow prejudgment interest only on liquidated or readily ascertainable amounts (a contract sum, an invoice) — and bar it on unliquidated damages (pain and suffering, most general tort damages). Confirm your claim qualifies on the state's page.
When it starts. The accrual date is claim-dependent — date of loss, breach, demand, or filing. You set it below; each state's page states the rule.

Rate series Claim amount (principal) ($)

Date interest begins accruing (claim-dependent) Date of judgment

Estimate for reference only — courts, agencies and creditors may apply different rounding or conventions. Not legal, tax, or financial advice.

The rate for each state is pulled from the same dataset as its prejudgment rate page and applied as simple interest, actual/365 (Colorado compounds annually per C.R.S. §5-12-102). These statutory rates have been stable for years, so the calculator accepts accrual dates back to 1990 at the current rate.

States covered

Each of these applies a fixed statutory prejudgment rate — as simple interest, except Colorado, which compounds annually:

State	Rate	Method	Statute
Alabama	6%	Simple	Ala. Code § 8-8-1
Colorado	8%	Compounded annually	C.R.S. 5-12-102
D.C.	6%	Simple	D.C. Code § 15-108
Georgia	7%	Simple	O.C.G.A. § 7-4-15
Idaho	12%	Simple	Idaho Code 28-22-104(1)
Kansas	10%	Simple	K.S.A. 16-201
Massachusetts	12%	Simple	M.G.L. c. 231, § 6B
Montana	10%	Simple	MCA 27-1-211
Nebraska	12%	Simple	Neb. Rev. Stat. sec. 45-104
New York	9%	Simple	N.Y. C.P.L.R. 5004
North Carolina	8%	Simple	N.C. Gen. Stat. 24-5
North Dakota	6%	Simple	N.D.C.C. § 32-03-04
Oregon	9%	Simple	ORS 82.010(1)(a)
Pennsylvania	6%	Simple	41 P.S. Sec. 202
Rhode Island	12%	Simple	R.I. Gen. Laws § 9-21-10
South Carolina	8.75%	Simple	S.C. Code Ann. § 34-31-20(A)
Utah	10%	Simple	Utah Code Ann. 15-1-1(2)
Washington	12%	Simple	RCW 19.52.010(1)
Wisconsin	5%	Simple	Wis. Stat. 138.04
Wyoming	7%	Simple	Wyo. Stat. Ann. Sec. 40-14-106(e)

Why other states aren't here

A prejudgment calculator is only honest when the rate is fixed and the compounding rule is deterministic. We leave out two groups on purpose, because a single computed number would be misleading:

Formula / variable-rate states (e.g. Florida, California, Texas — and Michigan, whose rate resets twice a year and also compounds) — the rate changed over the years the interest accrued, so the correct figure stitches together each period's rate. See the state page for the current rate and formula.
Discretionary states (e.g. Virginia, Connecticut, Tennessee) — a court decides whether to award prejudgment interest and when it starts, so there is no automatic amount to compute.

Federal-court judgments use a different statute and compound annually — use the federal post-judgment calculator. Browse every state's rate and rules on the prejudgment interest index.