September 22, 2026
Chaser's late payment calculator is a useful free tool tied to a broader debt-collection and credit-control software platform — more than most people need to calculate interest on one overdue invoice.
If you're chasing overdue payments across many clients regularly, Chaser's automated reminders and credit-control workflow solve a real operational problem beyond just the math — scheduled follow-ups, escalation rules, and payment tracking across an entire client base.
For a single overdue invoice, SMBkits' calculator handles both common cases — percentage-based interest owed, or a simple flat late fee — and gives you the number to put on the invoice or the reminder email, without adopting a collections platform to get there.
Which mode to use usually comes down to what your original invoice or contract terms specify. A percentage-based interest rate scales with how overdue and how large the invoice is, which feels proportionate on larger balances; a flat fee is simpler to communicate and apply consistently across smaller, similar-sized invoices — many freelancers prefer it specifically because clients don't need to do math to verify it.
If you're managing overdue payments at volume across many clients, Chaser's automated workflow earns its subscription. If you're handling one overdue invoice right now, the free calculator gets you the number in seconds.
| Feature | SMBkits | Chaser |
|---|---|---|
| Percentage interest calculation | Included | Included |
| Flat late fee mode | Included | Not the primary focus |
| Automated reminder scheduling | Not included | Core feature, paid |
| Account required | No | Required for the platform |
It depends on what your original contract or invoice terms state. A percentage-based interest rate scales with how overdue and how large the invoice is; a flat fee is simpler to communicate and apply consistently. Use whichever your terms specify — or decide upfront for future invoices.
Limits vary by state and by contract type — some states cap interest rates on commercial invoices. Check your state's rules, or your original contract terms, before charging a rate this tool doesn't automatically validate.