How to Write an Invoice: What It Must Include

An invoice is a request for payment. A good one tells the customer who you are, what they're paying for, how much, and what to do next. A clear one tends to get paid faster than a vague one.

This post covers how to write an invoice, using the UK list of required details from GOV.UK as the checklist, since it's specific and public. If you trade somewhere else, look up your own country's rules, because they differ.

What every invoice should show

GOV.UK says an invoice must include the following:

1. A unique identification number. This tells invoices apart.
2. Your name, address and contact details.
3. The customer's name and address.
4. A clear description of what you're charging for.
5. The date of supply, meaning when the goods or service were provided.
6. The invoice date.
7. The amount or amounts charged.
8. The VAT amount, if any.
9. The total amount owed.

Two details come up often for the self-employed. Sole traders should include their own name and any business name they use. If you use a business name, GOV.UK says to include an address where legal documents can be delivered to you.

Limited companies use the full company name as it appears on the certificate of incorporation.

Notice that the supply date and the invoice date are two separate items. You might finish a job on the 3rd and send the invoice on the 10th.

VAT invoices

If you and your customer are both VAT registered, GOV.UK says you must use a VAT invoice. It requires more information than a standard one, including your VAT number and the VAT shown separately. See GOV.UK's VAT invoice page for the full list, since it depends on the kind of sale.

If you aren't VAT registered, you don't charge VAT, and the VAT lines don't apply.

A simple layout

Put the things people look for in the places they look. One approach:

• Top: the word "Invoice," your invoice number and the invoice date.
• Left: your details. Right: the customer's.
• Middle: a table with one row per item, with a description, quantity, price and line total.
• Bottom: the total, how to pay, and when.

Here is an illustration of the middle table, with made-up numbers:

Describe each line so that the customer's accountant could understand it without calling you. "Consulting" is vague. "Website audit, 6 hours, 3 June" is not.

Numbering that stays out of your way

GOV.UK asks only for a unique number. It gives no format, so the system is yours to choose. Two common ones:

• A plain running count: 001, 002, 003.
• Year plus count: 2026-001, 2026-002.

Pick one and stick to it. If you cancel an invoice, record that rather than reusing the number. Gaps and repeats are what confuse an accountant or a tax inspector later.

Payment terms and how to be paid

Say when you expect payment and how. You might write "Due within 14 days" or give a specific due date, and then include bank details or the payment link you want people to use. Terms like "Net 30" mean payment is due 30 days after the invoice date, which is a common convention but not a rule: it's whatever you and your customer agree.

Agree terms before the work, ideally in writing, so the invoice confirms something the customer already knows. Pass-through costs, like the licence in the table above, should be listed as separate lines so that the customer sees what is yours and what is theirs.

Keep the copies

An invoice you send is a record of income, and income is what your tax return starts from. The IRS notes that self-employed people work out their profit by subtracting business expenses from business income, and report it on Schedule C. That only works if you can show both sides.

So save every invoice you issue in one place: a folder in Drive, a spreadsheet row, or both. Do the same for the invoices and receipts you receive. If you are unsure which is which, receipt vs invoice lays out the difference.

For the cost side of your records, the guide for freelancers shows how to get receipts filed without typing. ExpenseCatcher doesn't create or send invoices, but it can file the receipts and supplier invoices you forward to it.

Do this now

• Write your standard invoice once and save it as a template.
• Check it against the nine items above.
• Choose a numbering style and write down the last number you used.
• Create a folder for sent invoices.

This is general information, not tax or legal advice. Invoice rules depend on your country and tax status, so check with an accountant if you're unsure.