Late fee laws by state, cited to the statute

Set by formula or published periodically rather than fixed in statute, so it must be looked up for the period in question.

Federal Prompt Payment Act: federal agencies that fail to pay a business concern by the required payment date owe an interest penalty, accruing from the day after the required payment date until payment. The rate is not a fixed percentage in the statute: it is the rate established by the Secretary of the Treasury for interest payments under 41 U.S.C. § 7109(a)(1) and (b) (the Contract Disputes Act rate), published in the Federal Register and reset semiannually. Unpaid penalties are added to principal after 30 days and thereafter compound (31 U.S.C. § 3902(e)).

Not applicable in the state-usury sense; the Prompt Payment Act rate is set by statute/Treasury, not by contract. Federal law generally defers to state usury law for private contracts.

public

Applies to federal agencies paying business concerns for property or services. Interest penalty at the Treasury-set Contract Disputes Act rate (41 U.S.C. § 7109), published semiannually in the Federal Register; current rate available at fiscal.treasury.gov/prompt-payment. Construction subcontract flow-down provisions in 31 U.S.C. § 3905.

Governs federal-agency payments only; it does not regulate late fees between private businesses. Vendors invoicing federal agencies are entitled to the interest penalty automatically (no demand required for the initial penalty, § 3902(c)(3)).