⏰ Overdue Interest Calculator

✍ About this tool

The Overdue Interest Calculator is an online finance tool for individuals and businesses that need to know exactly how much extra interest a missed payment has generated. Credit card balances, bank loans, private lending between friends, supplier invoices paid late, or rent collected after the due date — anything with a "past due" label can be turned into a clear number here. You can enter the rate as an annual, monthly or daily figure, choose the day-count basis, and set any date range, so the result matches the wording of your contract rather than a rough guess.

When to use it

• Personal credit: estimate the penalty interest on a late credit card payment or an overdue loan instalment.
• Business invoices: quantify the late-payment charge a supplier can claim from a customer.
• Private lending: settle the interest when money borrowed from a friend or relative is returned after the agreed date.
• Rent and leases: apply the contractual late fee when a tenant pays rent after the due date.
• Legal claims: produce the interest figure a demand letter or small-claims filing asks you to specify.

How the calculation works

The calculator uses the simple-interest model that most contracts assume. The core formula is:
overdue interest = overdue principal × daily rate × overdue days
Where:

• Overdue principal: the amount that was due but not paid.
• Daily rate: derived from your input — a daily rate is used as-is, a monthly rate is multiplied by 12 and divided by the day-count basis, an annual rate is simply divided by the day-count basis. The basis is usually 360 (banker's year) or 365 (actual year).
• Overdue days: the number of days between the day after the due date and the settlement date.

Things to keep in mind

1. Simple vs. compound interest: this tool is simple interest only. Some lenders (credit cards in particular) charge interest on interest, so always follow the wording of your contract.
2. Regulatory caps: many jurisdictions cap late-payment interest, or require it to stay close to a reference rate such as a central-bank policy rate or SOFR. Amounts above the cap may not be enforceable.
3. Grace periods: banks and service providers often allow 1–3 days of grace. Payments made within the grace period normally incur no late interest.
4. Partial payments: if the debt is repaid in instalments, calculate each segment against its own outstanding balance, then add the results.

FAQ

Q: Why does the 360 vs. 365 basis matter?
A: A 360-day basis treats every year as 360 days, which slightly raises the daily rate for the same annual percentage; a 365-day basis follows the calendar. The difference is small per day but adds up over a long overdue period, so match the convention named in your contract.

Q: What is the difference between overdue interest and a late fee?
A: Overdue interest compensates the lender for the cost of money being tied up; a late fee or penalty clause is meant to discourage delay. Many jurisdictions apply a single cap to the combined total.

Q: Can I calculate a debt repaid in several instalments?
A: Yes, but do it in segments. After each repayment the outstanding principal is smaller, so later periods must be calculated against the new balance. This page handles one principal and one date range at a time.