Massachusetts late fee law

6%per year

Attaches to the debt by operation of law when you agreed no rate, so it accrues before any lawsuit and can be stated on a demand letter.

Note: Massachusetts also allows 12% PREJUDGMENT interest in contract actions under G.L. c. 231, § 6C, but that is added by the court after verdict and is not billable on an open invoice.

G.L. c. 107, § 3 is the PRE-SUIT contract-silent default: "If there is no agreement or provision of law for a different rate, the interest of money shall be at the rate of six dollars on each hundred for a year" (6% per annum), and a higher rate is not recoverable in an action unless the agreement to pay it is in writing. SEPARATE AND DISTINCT: G.L. c. 231, § 6C sets PREJUDGMENT interest in contract actions at the contract rate where established, otherwise 12% per annum, added by the clerk of the court after verdict and running from the date of breach or demand. That 12% is a litigation remedy - it is NOT a rate that accrues on an open invoice and must not be billed pre-suit; 6% is the figure that describes what is accruing on an unpaid Massachusetts invoice today. Sourcing caveat: malegislature.gov was unreachable from this environment, so the statutory text was taken from search extraction plus FindLaw (official path: Part I / Title XV / Chapter 107 / Section 3). Verify with counsel.

Parties may lawfully contract for any rate of interest (c. 107, § 3 expressly permits it), but rates above 6% must be in a written agreement to be recoverable. The practical ceiling is the criminal usury statute, G.L. c. 271, § 49: knowingly charging interest and expenses exceeding 20% per annum is criminal usury, unless the lender notifies the Attorney General of intent to engage in such transactions and keeps records (notification valid 2 years), or is a state/federally regulated lender. No general corporate-borrower exemption from § 49 was found; it applies to commercial loans as well.

public+private-construction

Public building construction (G.L. c. 30, § 39K): payment due within 15 days (30 for the Commonwealth) of a periodic estimate; late amounts accrue daily interest at 3 percentage points above the Federal Reserve Bank of Boston rediscount rate. Related public-work provisions at c. 30, §§ 39F–39G. Private construction Prompt Pay Act (G.L. c. 149, § 29E, 2010): applies to private projects with original contract price of $3M+ (excluding small residential); sets approval (15 days) and payment (45 days) deadlines but does not fix a special statutory interest rate. No general prompt-payment statute for ordinary private commercial (non-construction) invoices was found.

No Massachusetts statute specifically governing flat late fees on B2B trade invoices was found; the default rule applies - an agreed late fee is enforceable if it is a reasonable liquidated-damages provision rather than a penalty. Charges that function as interest above 6% must be agreed in writing (c. 107, § 3), and total interest-plus-charges exceeding 20%/yr can implicate criminal usury (c. 271, § 49) absent AG notification.