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Calculadora Capital

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? It is simple interest on the amount owed, counted by the days of delay. Enter the amount, the rate that applies to your case (4% for civil debts, around 10% for commercial ones) and the number of 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 (10.15% in the first half of 2026). For tax debts or 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, set every six months: in the first half of 2026 it is 10.15% (the ECB rate + 8 points, Decree-Law 62/2013). Tax debts to the State have their own rate, set annually. Choose the regime in the calculator or enter the rate from the notice in force.

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 10.15% rate of the first half of 2026, the interest would be €1,000 × 10.15% × 90 ÷ 365 = €25.03.

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?
For civil debts, 4% a year (Portaria 291/2003, unchanged). For commercial transactions between businesses, the rate is set every six months: in the first half of 2026 it is 10.15% (the ECB rate plus 8 percentage points). Tax debts to the State have their own rate, set annually.
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 (around 10% in 2026), applies to debts between commercial businesses and to commercial transactions, under Decree-Law 62/2013. It is revised every six months by a notice published in the official journal.
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, as long as you enter the correct rate. Late-payment interest on debts to the State (overdue taxes) follows the same formula, but has its own rate set annually (article 44 of the General Tax Law). Choose “Other rate” and enter the rate in force; the formula and the result are the same.

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Author: Thorben Rasmus Idel · Reviewed by: Nahar Geva · Last reviewed: 2026-06-05