An easy invoice is a correct invoice you can create in minutes. It has all the legally required fields, the right tax treatment, and clean numbering. This guide gives you three practical routes: a one-minute template, a simple Excel method, and when to move to software, plus the rules on VAT, IRPF, and the difference between full and simplified invoices.
You do not need software to issue a valid invoice today. The three options, in order of speed:
The payment method line and a “paid” stamp are optional. They help with collections but are not required for the invoice to be valid.
A full invoice must include these fields:
Numbering rule: keep a separate series per fiscal year and a separate series for rectifying invoices. Example: 2026-001, 2026-002. Never skip or reuse a number. If you need to change a sequence, start a new named series.
Totals at a glance:
A simplified invoice has fewer required fields and is mainly used for B2C sales. It is faster to issue and avoids collecting unnecessary customer data.
You can issue a simplified invoice when:
A simplified invoice must show at minimum: number and series, issue date, supplier NIF and name, description of goods or services, VAT rate, and the total (showing “VAT included” or the VAT amount).
You cannot use a simplified invoice for most B2B transactions, intra-EU supplies, or whenever the customer needs to deduct input VAT. In those cases issue a full invoice. If a customer requests a full invoice for any reason, issue one with their NIF and full details.
VAT:
IRPF:
Example:
Excel works well as long as the layout is clear and the maths are visible. Avoid complex nested formulas; keep calculations human-readable.
Header block: your name or business name, NIF, and address. Customer name and NIF if B2B. Invoice number and series. Issue date and delivery date if different.
Line items table: columns for description, quantity, unit price (excluding VAT), discount if applicable, and line subtotal.
Summary box: tax base, VAT rate(s) and VAT amounts, IRPF amount if applicable, total payable.
Footer: optional notes: payment method, bank IBAN, due date, purchase order reference, and any legal mention (exemption article, reverse charge, etc.).
Download the free Excel invoice template
Common Excel mistakes to avoid: broken numbering sequences, hidden decimal rounding that changes totals, and accidentally reusing last year’s series.
Export to PDF before sending. Archive both the Excel file and the PDF in a numbered folder.
A few habits keep the monthly invoicing routine quick and clean:
Handwritten invoices are legally valid if they are legible and contain all mandatory fields. Useful when working on-site or for occasional one-off transactions.
Two typical scenarios:
From 1 July 2027, any invoicing software used by a business or autónomo must be a certified invoicing system (SIF) compliant with the Verifactu standard (Royal Decree 1007/2023). A compliant system chains invoice records, prevents post-issue alteration, and adds a QR code to each invoice.
Word documents and standard Excel spreadsheets will not meet the Verifactu requirement after the deadline. Using non-certified software after 1 July 2027 can result in fines of up to €50,000 per year.
The right moment to switch is before the deadline rather than on it. Software gives you automatic numbering, VAT and IRPF calculations, a client registry, recurring invoices, and a built-in audit trail, benefits that apply well before the compliance deadline.
For the full detail on the Verifactu obligation, see the Verifactu guide.
Do I need invoicing software today? No. A spreadsheet or template is fine if the mandatory fields are present and correct. Plan your migration to certified software before 1 July 2027.
Are Excel invoices legal? Yes. The tool does not determine legality: the contents do. An Excel invoice with all mandatory fields and correct tax maths is legally valid.
Must I show “paid” or the payment method? No. Both are optional. Useful for collections but not required for the invoice to be valid.
Is a signature required? No. A signature is not a mandatory field. Authenticity and integrity come from correct record-keeping or from using compliant invoicing software.
Can I write invoices in English or another currency? Yes. Invoices can be in any language and currency. Any legal mentions that cite specific articles (exemptions, reverse charge) should be in Spanish. Show VAT amounts in euros.
When must I issue a rectifying invoice? When correcting an error or adjusting the tax base or VAT. Use a separate rectifying series and reference the original invoice number. Issue it before the 16th of the month following the VAT accrual date in B2B transactions.
renn is a gestoría with invoicing built for autónomos. It generates correct invoices automatically, applies the right VAT rate and IRPF treatment, maintains consecutive numbering series, and runs on a Verifactu-compliant certified system. For the step-by-step guide on creating invoices as an autónomo, see how to make a self-employed invoice. For the full list of mandatory fields, see mandatory invoice details. If you are not yet registered, renn handles autónomo registration online.
