How to write a professional invoice in 5 steps

A professional invoice does three jobs at once: it tells the customer what they owe, it gives them a way to pay, and it keeps your tax advisor happy. Miss any one of those and you get late payments, confused customers, or a tax headache.

1. Your business details and the customer's

Your full name or company name, address and tax number go at the top, then the customer's details. If you sell to other businesses (B2B), the customer's VAT ID belongs on the invoice too — without it, a reverse-charge invoice can be rejected.

2. A unique invoice number and date

Sequential invoice numbers are a legal requirement in most countries. Never skip or reuse a number — gaps in the sequence are exactly what a tax audit looks for. The date is also required, and for services you usually add the service period or delivery date.

3. Line items with quantity, unit price and tax

Each line needs a clear description, a quantity, a unit price, and the tax rate. A lump-sum 'work done €500' invites questions. Break the work into lines the customer can verify, and state the VAT rate per line.

4. The payment method and due date

Say exactly how you want to be paid and by when. A bank transfer needs your IBAN and BIC. In Germany and Austria, a SEPA QR code on the invoice lets the customer scan and pay in one tap — invoices with a QR code get paid measurably faster.

5. A machine-readable format

From 2025 Germany and other EU countries are moving to mandatory e-invoicing. A ZUGFeRD 2.2 / Factur-X PDF is both: a normal PDF a human reads, and a structured data file an accounting system reads automatically. Send that and your customer never re-types your invoice.

InvoYX builds all five elements for you — a ZUGFeRD e-invoice PDF with your details, a SEPA QR code, sequential numbering and tax handling — offline, in one flat-price app.