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Late-Payment Interest Calculator (Portuguese Juros de Mora)

How much late-payment interest (juros de mora) can you charge, or do you owe, on an overdue payment? In 2026 the rate is 4% for civil debts, 10.40% for commercial transactions between businesses (second half of the year) and 7.221% for tax debts to the State. Choose the regime (the rate is pre-filled), enter the amount owed and the days late, and this calculator estimates the interest and the total to pay.

Civil debts use the legal rate of 4%. For commercial transactions between businesses, the rate changes every six months (10.40% in the second half of 2026). For tax debts to the State, the rate is set each year (7.221% in 2026). For another situation, choose “Other rate” and enter the rate in force.

Late-payment interest
€9.86
Total to pay
€1,009.86

How the late-payment interest is reached

Amount owed€1,000.00
Interest per day late (4%/yr)€0.11/day
Interest on 90 days late€9.86
= Total to pay (debt + interest)€1,009.86

Educational estimate, not legal, tax or financial advice. It computes simple late-payment interest (amount × rate × days ÷ 365). Confirm the applicable rate and the date from which interest is due.

Video: how to use the calculator

What late-payment interest is

Late-payment interest (juros de mora) is the compensation a debtor pays for meeting an obligation late, that is, for paying after the deadline. It is simple interest: an annual rate is applied to the amount owed and multiplied by the fraction of the year the payment was overdue. It does not compound (no “interest on interest”), unlike the compound interest on savings.

The formula

Late-payment interest is: amount owed × annual rate × (days late ÷ 365). For example, €1,000 overdue for 90 days at the civil rate of 4% gives €1,000 × 4% × 90 ÷ 365 = €9.86 of interest. The total to pay is the amount owed plus the interest. The calculator also shows the interest that accrues for each day of delay.

Which rate applies to your case

The rate depends on the type of debt. Civil debts (between individuals, or from an individual to a company) use the legal rate of 4% a year, set by Portaria 291/2003 and unchanged since 2003. Commercial transactions between businesses (or with the State as debtor) use a higher rate, revised every six months: in the second half of 2026 it is 10.40% (the ECB rate plus 8 points, Decree-Law 62/2013, Aviso no. 16623/2026/2). Tax debts to the State (overdue IRS, VAT, IMI) use a rate set each year: 7.221% in 2026 (article 44 of the General Tax Law and Decree-Law 73/99, Aviso no. 18/2026/2). All three values are pre-filled in the calculator; for any other case, choose “Other rate”.

What about overdue loan instalments?

An overdue credit instalment (mortgage, personal or car loan) follows neither the civil nor the commercial rate: the bank applies the interest rate of the contract itself (the TAN) plus a surcharge of at most 3 percentage points (Decree-Law 58/2013). It may also charge a single recovery fee per overdue instalment, up to 4% of the instalment, with a minimum of €12 and a maximum of €150. These are legal ceilings; a given contract may charge less. To estimate, choose “Other rate” and enter your contract’s TAN plus the surcharge.

Worked example

Take a €1,000 invoice paid 90 days late, as a civil debt (the legal 4% rate): the late-payment interest is €1,000 × 4% × 90 ÷ 365 = €9.86, so the total to pay rises to €1,009.86. If it were a commercial debt between businesses, at the 10.40% rate of the second half of 2026, the interest would be €1,000 × 10.40% × 90 ÷ 365 = €25.64. And if it were overdue taxes, at the 7.221% rate for 2026, it would be €1,000 × 7.221% × 90 ÷ 365 = €17.81.

Frequently asked questions

How is late-payment interest calculated?
It is simple interest on the amount owed: amount × annual rate × (days late ÷ 365). On a €1,000 debt overdue for 90 days at the civil rate of 4%, the interest is €9.86. It does not compound: the rate always applies to the original amount owed, not to interest already accrued.
What is the late-payment interest rate in 2026?
It depends on the type of debt: 4% a year for civil debts (Portaria 291/2003, unchanged since 2003); 10.40% for commercial transactions between businesses in the second half of 2026 (the ECB rate plus 8 points, Aviso no. 16623/2026/2, up from 10.15% in the first half); and 7.221% for tax debts to the State throughout 2026 (Aviso no. 18/2026/2).
What is the difference between civil and commercial interest?
The civil rate (4%) applies to debts between individuals and to debts from individuals to companies. The commercial rate, much higher (10.40% in the second half of 2026), applies to debts between commercial businesses and to commercial transactions, under Decree-Law 62/2013, and is revised every six months by a notice published in the official journal. In commercial transactions the creditor is also entitled to a fixed €40 recovery indemnity per late payment, on top of the interest.
From when does late-payment interest run?
As a rule, from the day after the payment deadline (for obligations with a fixed term, such as an invoice with a due date). Count the days between when you should have paid and when you will pay, and use that number in the calculator.
Can I use this calculator for tax debts?
Yes: choose “Debt to the State / taxes”. Late-payment interest on tax debts (overdue IRS, VAT, IMI) follows the same formula, with the rate set annually under article 44 of the General Tax Law and Decree-Law 73/99: 7.221% in 2026, in force since 1 January. If the delay spans years with different rates, compute each period at that year’s rate and add the interest up.
What interest do I pay on an overdue loan instalment?
Credit contracts (mortgage, personal, car) use neither the civil nor the commercial rate: the bank charges the contract rate (TAN) plus a surcharge of at most 3 percentage points, and may charge a single recovery fee per overdue instalment, up to 4% of the instalment (minimum €12, maximum €150), under Decree-Law 58/2013. To estimate, use “Other rate” with your contract’s TAN plus the surcharge.

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Author: Thorben Rasmus Idel · Reviewed by: Nahar Geva · Last reviewed: 2026-08-03