How to write an invoice

Start with the essentials

A good invoice makes five things obvious:

1. Who is sending it
2. Who is being billed
3. What the charge is for
4. How much is due, and when
5. How to pay

If a customer has to email you to answer any of those, the invoice is making them work.

Write it, step by step

1. Add your business details

Your business or trading name at the top, with the contact details a customer might need. Add your logo if you have one, but keep the document a working document, not a brochure.

2. Add the customer's billing details

Use the name the customer expects to see. For a business, that often has to match the entity in their accounting or procurement system, so it is worth getting right the first time.

3. Give it a number

Number every invoice, and never reuse one. INV-0001, INV-0002 is plenty. Add a year if you find it useful (2026-001). Consistency is the whole point.

4. Add the dates

Show the issue date and the due date, both spelled out. A specific due date is harder to misread than a payment term on its own.

5. Describe what you supplied

One line per product, service, milestone or billing unit, with enough detail that someone who was not there understands what they are approving. For each line, show the quantity or units, the rate, and the line total.

6. Total it up

Subtotal first. Add discounts, tax or other adjustments on their own lines. Finish with one amount due that cannot be missed.

7. Say how to pay

Include the method and the details to use it. For a bank transfer, that means the account information and any reference you want quoted. Make paying you the path of least resistance.

8. Read it back

Check the name, number, dates, line items, tax and total. A thirty-second review prevents a week of back-and-forth.

A numbering scheme that lasts

Pick one and stick to it. A running count is the simplest thing that works:

• INV-0001
• INV-0002
• INV-0003

Prefix the year if it helps you find things later:

• 2026-001
• 2026-002
• 2026-003

If your tax rules prescribe a particular format, those come first.

When an invoice is overdue

Most late payments are oversights, not disputes, so start there. Send a short reminder that assumes the delay is administrative: the invoice number, the amount, the original due date, and the invoice attached again.

If it stays unpaid, follow whatever your contract or terms set out, keep the tone factual, and keep a record of what you sent and when.