Late Payment Interest Calculator
If your credit terms include a late-payment interest clause, you may be entitled to claim interest on overdue invoices. This calculator shows you exactly how much interest has accrued, what the total amount owed is today, and what it costs the debtor per day — useful information for a letter of demand.
How to read the result
The calculator shows the interest accrued to today on the invoice, the total amount now owed (principal plus interest), and a daily rate — useful for showing the debtor that the debt is growing every day they delay.
The days overdue figure counts from the invoice date you enter. If your contract specifies a payment due date that is later than the invoice date (e.g. "payment due 30 days from invoice"), enter the due date rather than the invoice date — interest typically starts accruing from the due date, not the invoice date, unless your terms say otherwise.
When to use this in a letter of demand
When you issue a formal letter of demand, quantifying interest serves two purposes: it increases the total amount stated as owed (which may motivate payment), and it demonstrates that you are tracking the account carefully. Use the figure from this calculator as the interest amount in your demand, and state that interest continues to accrue at $X per day until payment is received.
Use our letter of demand template — it includes a section for interest that you can complete using this calculator.
For more on the recovery process: How Merion's recovery process works.
This is an indicative calculation only — not legal or financial advice. Your entitlement to interest depends on the terms of your specific contract. If you are unsure whether you can claim interest, seek legal advice. Merion is not a legal firm and cannot advise on the enforceability of interest claims.
A letter of demand with interest gets results.
Use our free letter of demand template, or let Merion handle the whole recovery — commission-only.