How to write an invoice

An invoice is payable when it answers six questions without the reader having to ask you anything: who you are, who owes the money, which document this is, when it was issued, what it is for, and how and by when to pay. Get those six right and the rest is presentation.

Most invoices that go unpaid for weeks are not disputed. They are missing one of the six — usually a purchase-order reference or a clear due date — and they sit in someone's inbox waiting for a reply you never knew was needed.

What are the six things every invoice needs?

1. Your details. Your trading name, your address, and your tax registration number if you have one. If you are a registered company, your registration number too — in many jurisdictions that is a legal requirement, and everywhere it is what lets a finance team match you to a supplier record.

2. Your customer's details. The legal entity that owes the money, not the person who asked you for the work. Getting this wrong is the most common reason an invoice is bounced back: a company cannot pay an invoice addressed to an individual, and a subsidiary cannot pay one addressed to its parent.

3. A unique invoice number. One sequence, no gaps, never reused. See our guide to invoice numbering for why the gaps matter.

4. The issue date. And, separately, the date of supply if it differs — the tax point is usually the supply date, not the invoice date.

5. What you supplied. One line per item, each with a description a stranger can understand, the quantity, the unit price, and the line total. Then the subtotal, the tax, and the total due. "Consulting — £4,000" is not a description; "Discovery workshop, 2 days @ £2,000/day" is.

6. How and when to pay. The due date as an actual date, not "30 days". Your payment details, or a link to pay. If there is a purchase-order number, put it near the top — that is the field the accounts payable system matches on.

What is the difference between an invoice and a receipt?

An invoice is a request for payment. A receipt is proof that payment happened. They are issued at different moments and they serve different people: your customer needs the invoice to authorise payment, and their bookkeeper needs the receipt to close the entry.

Sending only a receipt when the customer expected an invoice is a common cause of late payment in businesses that take payment up front.

How should you describe line items?

Write for someone who was not in the room. The person approving your invoice is often not the person who hired you, and they are deciding whether to release money against a line they have no context for.

Bad: Services rendered — 12,000 Better: Website redesign — discovery and wireframes (phase 1 of 3) — 12,000

If your work is billed by time, state the rate and the quantity separately rather than folding them into a total. A rate that is visible is a rate that does not get queried.

What payment terms should you set?

Whatever you and your customer agreed — and then write the actual calendar date on the invoice. "Net 30" is a term of art that different finance teams count differently: from the invoice date, from receipt, or from the end of the month of receipt. A date cannot be misread. There is more on this in invoice payment terms explained.

Do you need to include tax?

If you are registered for VAT, GST or an equivalent, then yes, and the requirements are specific: tax shown per line or per rate, the rate itself, your registration number, and in many places the words "tax invoice". If you are not registered, do not show a tax line at all — an invoice showing 0% tax from an unregistered business invites a question you will have to answer by email.

How do you make it easy to actually pay?

The single biggest determinant of when you get paid is how much friction sits between the reader and the payment. In order of effectiveness:

1. A link that takes them straight to a payment page with the amount pre-filled.
2. A saved payment method, so a repeat customer pays in one click.
3. Bank details on the invoice, which requires them to leave and type things.
4. "Please contact us for payment details", which is how an invoice ages 30 days.

Frequently asked questions

What are the six things every invoice must include? Your details, your customer's details, a unique invoice number, the issue date, an itemised description of what you supplied with amounts, and how and by when to pay.

Can I write an invoice by hand? Yes, and it is legally valid in most jurisdictions provided it contains the required information. The practical problem is not validity but numbering and records: a handwritten sequence is easy to duplicate or skip, and you have no copy unless you remember to make one.

Do I need an invoice number? Yes. It is a legal requirement in most jurisdictions, and it is what lets you, your customer and both sets of accountants refer to the same document unambiguously.

When should I send an invoice? As soon as the work is done or the goods are delivered, unless you agreed otherwise. Payment terms usually run from the invoice date, so every day you delay sending is a day added to when you get paid.

What should I do if an invoice is wrong after I have sent it? Do not edit it. Issue a credit note against it and, if needed, a fresh invoice for the correct amount. Editing a sent invoice leaves you and your customer holding different documents with the same number.