Guide · 4 min read
How to write an invoice: what to include and what to avoid
A checklist of what a professional invoice should include, how to number invoices, and the small details that help you get paid on time.
A clear invoice makes it easy for a client to approve and pay you. A vague one gets queried, forwarded and left in an inbox. Here’s what to include and a few habits that help you get paid on time.
What every invoice should include
- The word “Invoice” clearly at the top.
- Your business name, address and contact details.
- Your customer’s name or company and their address.
- A unique invoice number.
- The issue date and the payment due date.
- A line for each product or service, with quantity, unit price and line total.
- Subtotal, any discount, tax (if you charge it) and the total amount due, with the currency.
- How to pay: bank details, payment link or accepted methods.
Requirements vary by country. If you are registered for VAT, GST or sales tax, your registration number and a breakdown of tax are usually mandatory. Check your tax authority’s guidance for the details that apply to you.
Numbering your invoices
Invoice numbers should be unique and follow a sequence, so you and your accountant can see that none are missing. Simple formats work best: 0001, 0002… or with a year prefix such as 2026-014. Never reuse a number, even for a cancelled invoice — issue a credit note instead.
Describe the work precisely
“Website work — £1,200” invites questions. “Homepage redesign: 3 layout concepts and 2 rounds of revisions (as per proposal dated 2 Sept)” doesn’t. Reference purchase order numbers or project names your client uses internally, so the invoice reaches the right person.
Set clear payment terms
Give a specific due date rather than only “Net 30”, and state it near the total. If you charge late fees, mention them on the invoice and make sure they were agreed in advance.
Create one in a few minutes
The free invoice generator covers all the fields above, calculates discounts and tax for you, and downloads a PDF. Nothing you enter is uploaded. If you need to check a tax figure first, the VAT calculator shows the net, tax and gross amounts.
Before you send it
- Double-check the client’s legal name and billing address.
- Make sure the totals match what was agreed.
- Save a copy of every invoice you send — you will need them for your records.