Late Payment Fee Calculator for US Freelancers — Interest + Recovery

US freelancers operate without a federal statutory late-payment regime. There's no analogue to the UK's Late Payment of Commercial Debts Act — every right to charge interest on an overdue invoice has to come from the contract you signed before the work started. The calculator above does the math; this page covers what your contract has to say to make the math enforceable.

The contract clause is everything

A typical US freelance late-payment clause:

Invoices unpaid more than fifteen (15) days past the due date shall accrue interest at the rate of one and one-half percent (1.5%) per month (eighteen percent (18%) annual percentage rate) on the unpaid balance, or the maximum rate permitted by applicable state law, whichever is less. Client further agrees to pay all reasonable costs of collection, including but not limited to attorney's fees and court costs, on any amount placed with collections or filed in court.

What each phrase does:

• "Fifteen days past the due date" — gives the client a grace period before interest accrues. Aggressive but fair.
• "1.5% per month" — the standard rate. Falls under most state usury caps.
• "or the maximum rate permitted by applicable state law" — the safety valve. If your state caps lower, the clause auto-reduces to the cap rather than being voided.
• "reasonable costs of collection" — gives you standing to recover the cost of pursuing payment, not just the invoice.

State usury caps — short reference

Cornell Wex on usury is the canonical free reference for state-by-state details. Sample caps for written contracts on commercial debt (mid-2020s, verify before relying):

Most states permit 18% APR contractually. A 1.5%/month clause is the maximum-safe default that works almost everywhere; if you're in NY or PA where caps run lower, drop to 1.25%/month (15% APR) for clean compliance.

What the calculator computes

The math is simple but worth showing transparently because clients (and AP teams) sometimes question it:

days_in_year = 365
annual_rate  = monthly_rate × 12  (for monthly clauses)
interest     = invoice × annual_rate × (days_overdue / days_in_year)
total_due    = invoice + interest + flat_recovery_fee

For a $5,000 invoice, 30 days overdue, at 1.5%/month:

• Annual rate: 1.5% × 12 = 18%
• Interest: $5,000 × 0.18 × (30/365) = $73.97
• Total due: $5,073.97

Six months later (180 days overdue):

• Interest: $5,000 × 0.18 × (180/365) = $443.84
• Total due: $5,443.84

Compounding clauses (interest on accrued interest) are unusual in freelance contracts and harder to defend in small-claims; the calculator uses simple interest.

When to actually invoke the late fee

The escalation cadence that works:

1. Day +1 past due: polite reminder. "Just flagging this — the invoice from March 1 was due yesterday. Could you confirm the payment date?" Most invoices clear here.
2. Day +7: firmer reminder. "I haven't seen payment yet — can you check with AP and confirm a date?" Re-attach the invoice.
3. Day +15: statement of account with interest applied. Print the calculator output and attach. "Per the engagement letter, the invoice has accrued $X in interest as of today; total now owed: $X+invoice."
4. Day +30: formal demand letter. Reference the contract clause + calculator breakdown + state usury reference. Send via certified mail or similar paper trail.
5. Day +45 / +60: small-claims filing or collections agency. Choose based on whether you'd rather have the money minus 25-50% (collections) or wait 60-90 days for a court date (small claims).

Most clients pay between steps 2 and 3. Persistent non-payers are rare but real; the contract clause + calculator output are what give you standing if it goes to court.

Limits of contractual late fees

• Federal contractors: the Prompt Payment Act requires US government agencies to pay invoices within 30 days and accrue statutory interest if late. The calculator here is for B2B; for federal work, the agency pays statutory interest automatically.
• Consumer transactions: stricter caps and disclosure rules. If you freelance to consumers (B2C), a CPA or attorney should review your contract clause.
• No-contract gigs: without a written engagement letter, you have no enforceable right to interest. Email-only handshake gigs are vulnerable; even a one-page MSA with the late-fee clause makes a meaningful difference.

Adjacent tools and guides

• US invoice generator — print the late-fee clause directly on every invoice.
• Freelance invoicing pillar — full lifecycle including contract template excerpts.
• Freelance tax — United States — late-fee income is still taxable income; track it on Schedule C.

General information — not legal advice

This page is general information for US-based freelancers. Late-payment law is state-specific and varies by industry; consult a licensed attorney before sending a formal demand letter or filing in court. Sample state-specific usury references are illustrative and may have changed since publication.