South Dakota late fee law

12%per year

We have not been able to confirm whether this figure is a contract-silent default, a litigation-only rate, or a ceiling. Do not rely on it without counsel.

Under an obligation to pay interest with no rate specified, interest is payable from the date the debt is incurred at a maximum of the Category C rate - 12% per year - as established in SDCL 54-3-16 (which sets Category A 4.5%, B 10%, C 12%, D 1%/month, E 4%, F 15%). Judgments and statutory liens bear the Category B rate (10%) under § 54-3-5.1. Verified on the official sdlegislature.gov site. Rate type not classified: SDCL 54-3-4 is phrased as a maximum ('at a maximum of the Category C rate'), so whether 12% accrues by default on a silent obligation or only caps an agreed rate is not resolved by the recorded text. Verify with counsel before relying on this figure.

No usury cap for written agreements: SDCL 54-3-1.1 provides there is no maximum interest rate or usury restriction between any entities if the rate is established by written agreement (physical or electronic), unless a maximum is specifically established elsewhere in the code. B2B parties may therefore contract for any rate in writing.

public

SDCL ch. 5-26 (Prompt Payment Act) covers government agencies: payment due per contract or within 45 days after receipt/acceptance and invoice; overdue amounts accrue interest at the Category B rate (10% per year, per § 54-3-16) or the contract rate (SDCL 5-26-3); interest under $5 need not be paid; pass-through prompt-payment duties to subcontractors under § 5-26-6. No prompt-payment statute found for private projects.

No SD statute specifically regulating flat late fees on B2B invoices was found; given § 54-3-1.1's written-agreement deregulation, agreed late charges in a signed B2B contract face little rate-based restriction, though liquidated-damages/penalty doctrine still applies to flat fees. Verify with counsel.