How to calculate late payment interest in Spain (worked example)

If a Spanish customer pays you late, Spanish law gives you interest from the first day of delay and a fixed recovery fee, with no need to warn them first. Few foreign suppliers claim either, usually because they don't know the rate or how Spaniards calculate it. This guide gives you the numbers and a template you can attach to your demand.

The legal basis in one paragraph

Spain implements the EU Late Payment Directive through Ley 3/2004. It covers payments between businesses, including sole traders acting in their trade (not consumers). The debtor falls into default automatically when the due date passes (article 5). Unless the contract sets a different rate, interest runs at the European Central Bank's main refinancing rate plus eight percentage points (article 7). On top, the creditor gets a fixed €40 in recovery costs "in all cases" and without having to ask, plus any higher costs it can prove (article 8). Without an agreed term, payment is due 30 days after delivery; an agreed term can't exceed 60 days (article 4).

Which law applies depends on your contract. If it's governed by Spanish law, or you're claiming before Spanish courts under it, these are your rules. Other EU countries have their own versions of the same Directive, with similar structures.

The current rate: 10.40 %

For the second half of 2026 (1 July to 31 December), the Spanish statutory rate is 10.40 %. It was set by the Treasury resolution of 30 June 2026, published in the Official State Gazette (BOE) on 1 July 2026: the ECB applied 2.40 % in its last main refinancing operation of the previous half-year, and 2.40 + 8 = 10.40.

The rate resets every six months. Before sending a claim, search the BOE for "tipo legal de interés de demora operaciones comerciales" plus the half-year you need. If the delay spans two half-years, apply each rate to its own days.

The formula

Interest = amount owed × annual rate × days late ÷ 365

• Start: the day after the due date.
• End: the payment date or, if still unpaid, the date of your claim. State that interest keeps accruing until payment.
• Base: the law refers to the amount owed. In Spanish practice the invoice total including VAT (IVA) is commonly used. For large sums or part payments, check with a Spanish lawyer.
• Year: the law doesn't specify 365 or 360 days. 365 is the usual choice and the hardest to dispute.

Worked example

A Portuguese packaging supplier delivers to a food producer in Murcia on 1 August 2026. No payment term was agreed, so the statutory 30 days apply: the €2,420 invoice falls due on 31 August. The customer pays on 30 November.

Item	Calculation	Amount
Days late	1 Sep - 30 Nov (30 + 31 + 30)	91 days
Daily interest	2,420 × 10.40 % ÷ 365	€0.69
Late payment interest	2,420 × 0.104 × 91 ÷ 365	€62.75
Fixed recovery costs	Article 8	€40.00
Extra on top of the invoice		€102.75

With several overdue invoices, the usual practice is to claim €40 per invoice and to calculate interest for each one from its own due date.

Using the numbers to get paid

The point of the calculation is usually leverage, not the extra €100.

• Put it in writing, in Spanish if you can. A short letter with principal, interest to date, €40 per invoice and a deadline reads very differently from a polite reminder. Spanish accounts departments recognise "intereses de demora (Ley 3/2004)" immediately.
• Offer to waive it. "We'll waive interest and the recovery fee if the principal is paid by 15 December" often unblocks a stuck payment. Confirm any deal by email.
• Prepare for the formal stage. Since April 2025, under Organic Law 1/2025, most Spanish civil claims require proof of a prior attempt to negotiate. A clear, itemised demand helps with that.

If the debt is undisputed and cross-border within the EU, a European Payment Order or the Small Claims Procedure may be options; our guide to collecting an unpaid invoice from a Spanish company walks through each stage. If the customer has gone quiet or changed number, start with how to locate a Spanish debtor.

Mistakes Spanish lawyers spot instantly

• Using the wrong half-year's rate. Always cite the BOE resolution you used.
• Counting from the invoice date instead of the due date.
• Applying Ley 3/2004 to a consumer. It only covers business-to-business (and business-to-public-sector) payments.
• Adding surcharges that are neither in your contract nor in the law. One unjustified figure undermines the rest.

For larger debts, a Spanish lawyer will tell you how your case fits into debt collection in Spain. For the calculation itself, all you need is the right dates, the formula and the rate published in the BOE.