Start from the problem, not the feature list
Charge interest on late invoices
Your terms say interest applies after 30 days. The hard part is not deciding to charge it; it is working it out correctly, adding it to the right invoice, and explaining it without a fight.
The situation
A client pays 45 days late, every time, because nothing happens when they do. You want a consequence that is fair, predictable and already written into the terms they accepted.
What goes wrong today
Interest gets calculated by hand on the day you finally lose patience, so it is inconsistent and arguable. The amount lands as a separate invoice nobody connects to the original, or it never gets charged because the arithmetic was not worth the argument.
How it works in Invoice My Clients
Set the annual rate, the grace period and whether interest compounds once in Settings, and change it on an invoice where a contract says otherwise (Starter plan and above). Interest accrues on the overdue invoice itself: the balance the client sees on the payment page and in every reminder is the current one, with the interest shown as its own line. Where a flat late fee fits better, charge that instead. The late fee calculator on the free tools pages gives you the number before you commit to a policy.
When it does not fit
| Situation | What happens | What you do |
|---|---|---|
| Your state or the client's contract caps the rate | The app applies the rate you set and does not check the law | Set a rate within the cap; ask your accountant or attorney if unsure |
| The client is a consumer, not a business | Consumer rules differ by state | Check before switching interest on for consumer invoices |
| You want to waive it for one client | Interest is set on each invoice from your default | Switch it off on that client's invoices; nothing changes for the others |
| You are on the Free plan | Interest and late fees are on Starter and above | Upgrade, or note the terms on the invoice |
Where this lives in the product
Free tools
Questions people ask
Does interest start on the due date?+
It starts after the grace period you set, counted from the due date.
Will the reminders mention it?+
Yes. Reminders quote the current balance, interest included, and the payment link collects that amount.
Can I charge interest and a flat fee?+
Both exist and both can be on. Most owners pick one so the invoice stays easy to explain.