§ StatuteRates

Statutory interest calculators

Every calculator applies the governing statute's actual method — the right rate for the right period, the right compounding rule, with the source cited. Powered by the same dataset behind our free API.

Federal post-judgment interest

3.95%
The §1961 method: H.15 weekly rate for the week before judgment, daily accrual, compounded annually.

IRS interest (underpayment & refund)

7%
Quarterly §6621 rates compounded daily per §6622, across every rate change since 2017.

State judgment interest

10%
California, New York (incl. the 2% consumer rate), Massachusetts, and Treasury-linked Iowa.

Prejudgment interest (fixed-rate states)

9%
Interest before judgment for the 19 states + D.C. with a fixed statutory rate — simple, or Colorado’s annual compounding.

Late payment interest (UK & EU)

11.75%
UK Late Payment Act 1998 (base + 8pp, fixed at overdue date) and the EU Directive rate.

Why these are different

Most online calculators hardcode a rate that quietly goes stale. These pull from a dataset that re-verifies against official sources on a schedule, keep the full effective-date history (so a 2024 judgment gets 2024's rate, not today's), and implement the statutory computation — daily compounding for the IRS, annual compounding for federal judgments, fixed-at-overdue-date for UK late payment — rather than a generic percentage formula.