PopPay

Late Payment Interest Calculator (South Africa)

Work out simple interest on an overdue invoice from due date to payment date, with the in duplum cap applied automatically. Free, no signup.

Can you charge interest on overdue invoices?

Yes. If your terms specify a rate, that rate applies. If not, the prescribed rate of interest applies by default — it changes with the repo rate, so confirm the current figure in the Government Gazette before relying on it.

How the calculation works

Simple interest: amount × annual rate ÷ 365 × days overdue. Under the in duplum rule, arrear interest stops accruing once it equals the outstanding principal.

The better fix: invoices that chase themselves

Interest is leverage, but consistent follow-up is what actually gets SA invoices paid. PopPay sends polite reminders on a schedule and stops the moment payment reflects — free forever.