You did the work. They didn't pay. Now what?
If you're a freelancer, contractor, or small business owner, you already know the sick feeling. The invoice was due three weeks ago. You've sent two "just checking in!" emails. The client read them. They still haven't paid. And every day that goes by, you're effectively giving them an interest-free loan with your own money.
The good news: you almost certainly have the legal right to charge a late fee — and adding one (correctly) is often the single thing that gets a stalled invoice paid. Here's how to figure out exactly how much you can add, and how to send a reminder that actually works.
How much late fee can you legally charge?
There's no single national number — it depends on where you and your client are based and what your contract says. But here are the realities most independent invoicers run into:
If your contract or invoice already states a late fee: You can charge what you agreed to, as long as it's reasonable. A flat fee (e.g. $25–$50) or a monthly percentage (commonly 1%–1.5% per month, which is 12%–18% annualized) are both standard and widely accepted.
If you said nothing about late fees: Many jurisdictions still let you charge a "reasonable" rate, but you're on much firmer ground if it was disclosed up front. Going forward, put a late-fee clause on every invoice.
Watch the cap: Some states and countries cap the maximum interest rate you can charge. Charging above the cap can make the fee unenforceable, so you want a number that's firm but defensible — not punitive.
The math is where most people freeze. Calculating 1.5% per month, prorated for 47 days overdue, on a $3,200 invoice, while staying under your local cap? That's exactly the kind of thing you don't want to eyeball at 11pm.
The reminder that gets you paid
Tone matters more than people expect. A panicked or aggressive email makes clients defensive. A calm, professional, numbers-on-the-table reminder makes paying feel like the easy option. The formula that works:
State the facts plainly: invoice number, original amount, due date, and how many days overdue it is.
Show the late fee that's now accruing: "Per our agreed terms, a late fee of 1.5% per month now applies, currently $X."
Give a clear new deadline and an easy way to pay.
Stay polite but firm. You're not asking for a favor — you're collecting money you earned.
Seeing the fee in writing reframes the whole situation. Suddenly "I'll get to it" becomes "let me pay this before it grows."
Do it in 60 seconds instead of an hour
Instead of digging through state statutes and fighting with a spreadsheet, you can plug in your invoice amount, due date, and late-fee terms and get the exact figure plus a ready-to-send reminder. I put together the Late Fee & Overdue Invoice Calculator for exactly this — it tells you how much you can add and generates a professional reminder you can send to your client today.
Calculate your overdue invoice late fee here and send the reminder before you close your laptop tonight.
The takeaway
An unpaid invoice isn't a lost cause and it isn't free money for your client. Charge a reasonable, disclosed late fee, send a clear professional reminder with the number attached, and you'll recover far more of what you're owed — usually faster than you'd expect. The clients who "forgot" tend to remember real quick once the meter is running.
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