What is late-payment interest (juros de mora) and how is it calculated?

What is late-payment interest?

Late-payment interest (in Portuguese, juros de mora) is the compensation a debtor pays for meeting an obligation late, that is, for paying after the deadline¹. «Mora» is the legal term for the delay in meeting an obligation. Whenever an amount due is not paid on the agreed date, late-payment interest starts running in the creditor's favour, until payment.

It is the kind of interest we run into without noticing: on an invoice paid past its due date, on overdue rent, on a tax settled late, or on a debt between businesses. This article explains how it is calculated, which rate applies to each case, and walks through a worked example. To run the numbers on your case, use our late-payment interest calculator.

How is late-payment interest calculated?

Late-payment interest is simple interest: an annual rate is applied to the amount owed and multiplied by the fraction of the year the payment was overdue¹. The formula is:

Late-payment interest = amount owed × annual rate × (days late ÷ 365)

Note two important details:

• It does not compound. The rate always applies to the original amount owed, never to interest already accrued. It is the opposite of the compound interest on savings, where interest earns more interest.
• It is counted by days. Divide the number of days late by 365 to get the fraction of the year. The longer the delay, the larger the interest.

The total to pay is then the amount owed plus the late-payment interest.

What is the late-payment interest rate in 2026?

This is where most confusion arises, because there is no single rate: it depends on the type of debt.

Civil debts: 4%

For civil debts (between individuals, or from an individual to a company), the legal interest rate of 4% a year applies, set by Portaria n.º 291/2003 and unchanged since 2003². It is the default in our calculator and the one used in most everyday situations.

Commercial transactions: around 10%

For commercial transactions between businesses (or where the State is the debtor), a higher statutory rate applies, under Decree-Law n.º 62/2013, which transposed the EU directive against late payment³. This rate equals the European Central Bank interest rate plus 8 percentage points and is set every six months by a notice published in the official journal. In the first half of 2026 it is 10.15%⁴. Because it changes every half-year, always check the notice in force.

Tax debts to the State

Overdue tax debts (IRS, IMI, VAT, etc.) have their own late-payment interest rate, set annually under article 44 of the General Tax Law. The calculation is the same; only the rate differs. In the calculator, choose “Other rate” and enter the tax rate in force.

What is the difference between civil and commercial interest?

The distinction is mostly about who owes whom:

• The civil rate (4%) covers relationships between individuals and debts from individuals to companies (for example, a consumer paying an invoice late).
• The commercial rate (≈ 10%) covers debts between commercial businesses and the commercial transactions covered by Decree-Law 62/2013 (for example, a company paying a supplier late)³.

The difference is significant: at the commercial rate, the interest on the same delay is more than double that of the civil rate. Hence the importance of correctly identifying the regime before doing the maths.

From when does late-payment interest run?

As a rule, late-payment interest runs from the day after the payment deadline, when the obligation has a fixed term, the typical case of an invoice with a due date: if it is not paid on that date, the debtor is automatically in default¹. In practice, count the days between when you should have paid and when you will pay, and use that number in the calculator.

Worked example

Take a €1,000 invoice paid 90 days late.

As a civil debt (the legal 4% rate):

• Late-payment interest = €1,000 × 4% × 90 ÷ 365 = €9.86.
• Total to pay = €1,000 + €9.86 = €1,009.86.

As a commercial debt between businesses (the 10.15% rate of the first half of 2026):

• Late-payment interest = €1,000 × 10.15% × 90 ÷ 365 = €25.03.
• Total to pay = €1,025.03.

The same delay, on the same amount, produces very different interest depending on the regime. Run the numbers on your case in the late-payment interest calculator and see the logic of simple interest in the simple interest calculator.