Interest on unpaid invoices in New Hampshire: no single rate if none was agreed; the most you can set depends on the deal

New Hampshire's rate when no rate was agreed

It depends: see N.H. Rev. Stat. Ann. § 336:1. 10% a year in business transactions in which interest is paid or secured, unless otherwise agreed in writing (RSA 336:1, I). Consumer credit transactions (RSA 358-K:1, V — consumer credit sales or loans) are NOT subject to that 10%. Interest on judgments, including prejudgment interest, floats: 26-week Treasury bill discount rate at the last auction before the end of September + 2 points, set yearly by the state treasurer (RSA 336:1, II). In an action on a debt or account stated, absent an earlier demand, interest runs from when suit is filed (RSA 524:1-a).

• “The annual rate of interest in all business transactions in which interest is paid or secured, unless otherwise agreed upon in writing, shall equal 10 percent. No consumer credit transaction, as defined in RSA 358-K:1, V, shall be subject to this paragraph.” — N.H. Rev. Stat. Ann. § 336:1, I (Rate of Interest), read November 6, 2026
• “The annual simple rate of interest on judgments, including prejudgment interest, shall be a rate determined by the state treasurer as the prevailing discount rate of interest on 26-week United States Treasury bills at the last auction thereof preceding the last day of September in each year, plus 2 percentage points, rounded to the nearest tenth of a percentage point.” — N.H. Rev. Stat. Ann. § 336:1, II, read November 6, 2026
• “In the absence of a demand prior to the institution of suit, in any action on a debt or account stated or where liquidated damages are sought, interest shall commence to run from the time of the institution of suit.” — N.H. Rev. Stat. Ann. § 524:1-a (Interest to be Added), read November 6, 2026

The most you can set in New Hampshire

For a homeowner: It depends: see RSA 336:1 and RSA 358-K.

For a business customer: It depends: see RSA 336:1. RSA 336:1, I sets 10% 'unless otherwise agreed upon in writing' and allows other than simple interest if agreed in writing.

• “a sale of goods or services in which the seller is a creditor, the buyer is a” — N.H. Rev. Stat. Ann. § 358-K:1 (Definitions) — consumer credit sale, read November 6, 2026
• “a consumer credit sale or a consumer loan.” — N.H. Rev. Stat. Ann. § 358-K:1, V — consumer credit transaction, read November 6, 2026
• “If agreed upon in writing, interest on business transactions may include charging other than simple interest.” — N.H. Rev. Stat. Ann. § 336:1, I, read November 6, 2026

Late fees in New Hampshire

See the state's words below.

• “including but not limited to origination fees, loan discount, transaction costs,” — N.H. Rev. Stat. Ann. § 358-K:1 — other charges, read November 6, 2026
• “This section does not preclude the collection or retention by the creditor of delinquency charges.” — N.H. Rev. Stat. Ann. § 358-K:2, IV, read November 6, 2026

Does New Hampshire want it agreed in advance?

Agreed in advance: yes, in the cases below. In business transactions, a rate other than 10% (and anything other than simple interest) must be agreed in writing (RSA 336:1, I). It does not apply to consumer credit transactions.

• “unless otherwise agreed upon in writing, shall equal 10 percent.” — N.H. Rev. Stat. Ann. § 336:1, I, read November 6, 2026

Homeowners and businesses in New Hampshire

The 10 percent is for business transactions; no consumer credit transaction, as defined in RSA 358-K:1, V, shall be subject to this paragraph (RSA 336:1, I).

• “No consumer credit transaction, as defined in RSA 358-K:1, V, shall be subject to this paragraph.” — N.H. Rev. Stat. Ann. § 336:1, I, read November 6, 2026

Prompt payment on private construction in New Hampshire

Not found in our check for New Hampshire.

Work out a late charge in New Hampshire

Set your own rate.

What was not checked for New Hampshire

• New Hampshire's 2026 judgment interest rate could not be read: the Judicial Branch page refused automated reading.
• No general New Hampshire maximum rate was found, but the text read does not say there is none.
• New Hampshire's late-charge limit for motor vehicle sales (RSA 361-A) was seen only in a summary and is not quoted.

Check New Hampshire's own text

Before you charge: read N.H. Rev. Stat. Ann. § 336:1, I (Rate of Interest) and the other New Hampshire texts quoted on this page, or ask a lawyer. As of November 6, 2026.

This is a plain-words summary of each state's own laws as of November 6, 2026, not legal advice. Rules have exceptions. Check the state's own text, linked on every state's page, or a lawyer before you charge a late fee or interest.

Compare New Hampshire with every state's answer, or with its neighbours just below.

Next door to New Hampshire

• Maine: floats if none agreed, depends by agreement
• Massachusetts: 12% if none agreed, depends by agreement
• Vermont: 12% if none agreed, depends by agreement

Official sources for New Hampshire

• N.H. Rev. Stat. Ann. § 336:1, I (Rate of Interest) — read November 6, 2026
• N.H. Rev. Stat. Ann. § 524:1-a (Interest to be Added) — read November 6, 2026
• N.H. Rev. Stat. Ann. § 358-K:1 (Definitions) — consumer credit sale — read November 6, 2026
• N.H. Rev. Stat. Ann. § 358-K:2, IV — read November 6, 2026

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