⏳Late Payment Interest Calculator

Interest calculator — statutory default and contractual interest

Our free interest calculator lets you instantly calculate default interest or contractual interest on an outstanding amount. Simply enter the claim amount, select the interest type and specify the period — either as a date range or a number of days. The calculator applies the formula: amount × (rate / 100) × (number of days / 365) and immediately shows the accrued interest and the total amount payable. It supports statutory default interest (Art. 481 of the Civil Code), statutory capital interest (Art. 359 of the Civil Code) and any contractual interest with a custom rate.

When does default interest accrue?

Default interest is owed to the creditor when the debtor fails to pay on time — even if the delay was not the debtor's fault. It is widely used for B2B invoices, private loans, damages and court-awarded amounts. The rate is set by the National Bank of Poland's reference rate plus a statutory margin. Since the NBP rate changes based on Monetary Policy Council decisions, it is always worth checking the current value and manually correcting the rate field in the calculator if needed.

Full privacy — calculations done locally

All calculations are performed directly in your browser. No amount, date or interest rate you enter is sent to any server. The calculator requires no registration, login or installation — it works immediately and remembers your last data after a page refresh.

Frequently asked questions

How do I calculate statutory default interest?

Statutory default interest is calculated using the formula: amount × (rate / 100) × (number of days / 365). The current statutory default interest rate is 11.25% per annum (NBP reference rate + 10 p.p.), but it may change when the reference rate changes. Our calculator performs this calculation automatically once you enter the amount, rate and period.

What is the difference between statutory default interest and statutory capital interest?

Statutory default interest (Art. 481 of the Civil Code) is charged when a debtor is late in payment — its rate is the NBP reference rate + 10 p.p. Statutory capital interest (Art. 359 of the Civil Code) applies when a contract does not specify an interest rate — its rate is the NBP reference rate + 3.5 p.p. Both rates change with decisions of the Monetary Policy Council.

Is the calculator result legally binding?

No. The result is indicative and is intended solely for a preliminary assessment of the interest amount. Statutory rates change with the NBP reference rate, and in court proceedings the accrual of interest may be subject to additional rules. Consult a lawyer or financial adviser before making any decision.