North Carolina late fee law

8%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.

'Except as otherwise provided in G.S. 136-113, the legal rate of interest shall be eight percent (8%) per annum for such time as interest may accrue, and no more.' This 8% legal rate applies when no rate is agreed. Per secondary sources, G.S. 24-5 applies the contract rate (or the 8% legal rate if none is stated) to amounts due on contract from breach as prejudgment interest - that section's text was not directly verified this session (official ncleg.gov blocked automated access; text corroborated via FindLaw/Justia).

G.S. 24-1.1: where the principal exceeds $25,000, parties may agree in writing to any rate; at $25,000 or less, agreed rates are capped by the statutory schedule (the greater of 16% or the rate announced monthly by the Commissioner of Banks - verify exact mechanics of § 24-1.1(c)). More importantly for B2B, G.S. 24-9 (verified via Onecle full text): an 'exempt loan' - loan of $300,000 or more, OR any borrower that is not a natural person (corporations, LLCs, etc.), OR a natural person borrowing primarily for non-personal/family/household purposes - may bear 'interest at any rate and fees and other charges in any amount that the borrower agrees to pay,' and 'a claim or defense of usury is prohibited in an exempt loan transaction.' Knowing usury (where caps do apply) forfeits all interest, with twice interest paid recoverable.

public+private-construction

Public construction: G.S. 143-134.1 - prime contractors must pay subcontractors within 7 days of receiving each periodic/final payment; payments delayed beyond that accrue interest at 1% per month or fraction thereof (excess retainage likewise bears 1%/month), plus owner final-payment interest rules for primes. Private construction: G.S. ch. 22C (§ 22C-5) - subcontractors must be paid within 7 days of the higher tier's receipt of payment; late/wrongfully withheld amounts accrue 1% per month. No prompt-payment statute found for ordinary non-construction private commercial invoices.

For ordinary commercial invoices, agreed flat late fees default to the liquidated-damages/penalty reasonableness test. Chapter 24 also contains provisions regulating late-payment charges on loans within its scope; because B2B/entity credit is largely 'exempt' under G.S. 24-9 (any agreed fees enforceable, usury defense barred), agreed late charges between businesses face little Chapter 24 risk - verify specifics with counsel.