How do I write an invoice?

Add your details, add the client's details, give it a unique sequential number, list the work with quantity and rate, add any tax and check the total, then set a specific due date and include complete payment instructions.

What must be on an invoice?

The word invoice, a unique invoice number, your name and address, the client's name and address, the issue date, a due date, an itemised description of the goods or services with quantity and rate, the subtotal, tax and total, and how to pay.

Should an invoice have a due date?

Yes, and it should be a specific calendar date rather than a term like 'net 30'. A specific date removes ambiguity and makes a late payment much easier to chase.

What is the best invoice numbering system?

A continuous sequence such as INV-001, INV-002, with no gaps and no restarting each month. If you cancel an invoice, keep its number and mark it void.

How to write an invoice

An invoice has one job: to get you paid without the client having to ask you a single question. Most late payments are not refusals — they are invoices that were unclear, missing something, or sent to the wrong person.

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What every invoice must contain

Element	Why it matters
The word "Invoice"	Distinguishes it from a quote or receipt. Accounts systems look for it.
A unique invoice number	How both sides refer to it. Required by most tax authorities.
Your name, address, contact	Who is being paid, and where to ask questions.
Client name and address	Their accounts team needs it for their own records.
Issue date	Starts the payment clock.
Due date	A specific date, not "net 30".
Itemised work	Description, quantity, rate, amount per line.
Subtotal, tax, total	Shown separately so the tax is auditable.
Payment instructions	Exact bank details or payment link.

The six steps

1. Add your details

Business name, address and an email you actually monitor. If you are registered for tax, include your registration number — many companies cannot process a supplier invoice without it, and chasing it afterwards adds a week.

2. Add the client's details

Address the invoice to the legal entity, not the person who briefed you. "Acme Ltd" gets paid; "Sarah" gets forwarded and forgotten. If they gave you a purchase order number, put it on the invoice — without it, many large companies will simply not pay.

3. Number it

Use a continuous sequence: INV-001, INV-002. Do not restart each month or leave gaps; if you cancel an invoice, keep its number and mark it void. Some freelancers start at a higher number such as INV-100 so a first client cannot tell they are the first.

4. List the work

One line per deliverable, with quantity and rate. Be specific. "Design work — 1 — 2,000" invites questions; "Homepage design, 3 concepts and 2 revision rounds — 1 — 2,000" does not. Vague lines are the single most common reason an invoice sits unapproved.

5. Add tax and check the total

Show the subtotal, then tax, then the total. If you give a discount, apply it before tax — tax is calculated on the discounted amount, and getting this backwards overcharges your client.

6. Set terms and payment details

State a specific due date. Include complete payment details: account name, number, sort code or IBAN, and SWIFT for international payments. Every detail they have to request is another week of delay.

When to send it

Send it the day the work is delivered. An invoice sent two weeks later signals that you are not tracking it closely, and it drops to the bottom of their queue.

Also learn when your client runs payments. Many companies pay on fixed cycles — once or twice a month. Missing a cut-off by one day can cost you two weeks, and simply asking "when is your payment run?" is often the single highest-value question you can ask.

Mistakes that delay payment

Sending it to one person. If they are on holiday, your invoice is too. Copy the accounts address.
No purchase order number when the client requires one.
Vague descriptions that the approver cannot match to work they recognise.
Missing or wrong bank details. Obvious, and still common.
Arithmetic errors. One wrong total and the whole invoice bounces back.
No due date, which quietly means "whenever".

If it is not paid

Day after due: a short, friendly email. Assume it was overlooked, because it usually was.
One week late: phone or message whoever briefed you. Email alone is easy to ignore.
Two weeks late: contact accounts directly and ask for a payment date, not an apology.
A month late: a formal reminder noting any late-payment terms, and pause further work.

Staying polite matters. Most late payments are administrative, not malicious, and the person reading your email is rarely the person who delayed it.

Make one now

Our free generator covers every element above, does the maths, numbers invoices sequentially and exports a clean PDF. No signup, and nothing you type leaves your browser.

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