How to write an invoice
What belongs on an invoice, how to number it and how to set terms that people actually follow. Includes a worked example and wording you can copy.
To write an invoice, put these on one page: the word "Invoice", a unique number, the invoice date, the date you did the work, your business name and contact details, your customer's name and address, a line for each thing you're charging for, any tax, the total owed, the date it's due and how to pay.
That's the whole job. The rest of this guide is about the details that decide whether it gets paid on time or sits in someone's inbox: a due date that is an actual date, a description the customer recognises, and a way to pay that takes no effort.
What to include on an invoice
Rules depend on where you trade. In the UK, GOV.UK lists what an invoice must include: a unique identification number, your name, address and contact details, the customer's name and address, a clear description, the supply date, the invoice date, the amounts charged, any VAT and the total owed. Sole traders must show their own name as well as any business name. Limited companies must use the full registered name.
In the US, the IRS page on what records to keep treats invoices as supporting documents for your books and sets out no fixed layout. Sales tax rules are set by each state, so check yours. The GOV.UK list is still a good standard to work to anywhere, because it covers what a customer's bookkeeper needs too.
| Item | Why it earns its place |
|---|---|
| Invoice number | Lets you and the customer talk about the same document, and lets a payment be matched to it |
| Invoice date and work date | The first starts the clock on payment. The second shows when the job happened |
| Your details | Your legal name, address, phone and email, plus a tax number if you have one |
| Customer details | The person or company that owes the money, not just whoever called you |
| Line items | What you did, how many, at what rate. Vague lines get queried |
| Tax | Shown on its own line if you charge it |
| Total and balance due | The total, less any deposit already paid, so nobody has to work it out |
| Due date | A calendar date |
| How to pay | A link, or bank details, or both, and what reference to use |
Ask business customers one question before you invoice: do you need a purchase order number on this? A missing PO number is a common reason an invoice gets bounced back by an accounts department weeks after you sent it.
A worked example
An electrician rewires a garage and fits two outside lights. The customer paid a $200 deposit when they accepted the quote. The local sales tax in this example is 7%, charged on materials only. Whether labour is taxed varies by state, so this is only an illustration.
| Description | Qty | Rate | Amount |
|---|---|---|---|
| Labour: rewire detached garage, fit two outside lights | 6 hours | $85.00 | $510.00 |
| Materials: cable, breaker, two LED wall lights | 1 | $150.00 | $150.00 |
| Subtotal | $660.00 | ||
| Sales tax, 7% on materials | $10.50 | ||
| Total | $670.50 | ||
| Deposit received Oct 3 | -$200.00 | ||
| Balance due by Nov 14, 2026 | $470.50 |
Above that table sit the invoice number (INV-0142), the date (Oct 31, 2026), the work dates, both parties' details and the job address. Below it sit the payment instructions and one line of thanks. The customer can see what they bought, what they already paid and what's left. Nothing needs explaining.
How to number invoices
Numbers have one job: never repeat. Pick a format and stay with it.
| Format | Example | Good for | Watch for |
|---|---|---|---|
| Plain sequence | 0142 | Anyone starting out | Tells a customer roughly how many invoices you've sent |
| Prefix and sequence | INV-0142 | Most small businesses | Nothing much. This is the safe default |
| Year and sequence | 2026-0142 | Finding things by year | Decide up front whether the count restarts each January |
| Customer code and sequence | HILL-007 | A few regular accounts | Harder to prove you haven't skipped one |
If you're VAT registered in the UK, HMRC's record keeping notice asks for "a sequential number based on one or more series which uniquely identifies the document". So a run that goes in order is a requirement there, not just tidiness.
When you make a mistake on an invoice that's already gone out, leave it on the books. Issue a credit note against it and send a new invoice with the next number. Deleting it and reusing the number is what causes confusion at tax time. The difference between these documents is covered in invoice, receipt or credit note.
Payment terms that work
Terms are what you agreed, so settle them before the job starts. Put them on the quote, then repeat them on the invoice.
| Term | Means | Suits |
|---|---|---|
| Due on completion | Pay when the job's done | Household customers, small repairs |
| Due on receipt | Pay now. Vague, because "now" has no date to chase | Avoid it. Write the date |
| Net 7 or Net 14 | Pay within 7 or 14 days of the invoice date | Most small jobs and repeat customers |
| Net 30 | Pay within 30 days of the invoice date | Companies with a monthly payment run |
Whichever you use, print the date itself. "Net 14" asks the customer to do arithmetic. "Due by November 14" doesn't. It also gives you a clean date to chase from, and the payment reminder wording depends on having one.
If you never agreed a date, the law may set one. For business customers in the UK, GOV.UK says payment is late 30 days after the customer gets the invoice or you deliver the work, whichever is later. An agreed date between businesses usually can't go past 60 days unless that's fair to both. Elsewhere, check your local rules.
Wording to copy
A payment terms line for the bottom of the invoice:
Payment is due by November 14, 2026. Pay by the link above or by bank transfer to the account shown, using invoice number INV-0142 as the reference.
A late fee line, only if your agreement with the customer included one and it's allowed where you are:
As agreed in our quote, invoices unpaid after the due date carry a late fee of 1.5% per month on the balance.
The email or text that goes with it:
Hi Dana, here's the invoice for the garage rewiring, $470.50 after your deposit. It's due by November 14 and you can pay it from the link. Thanks for having me out. Any questions, just reply here.
A note for regular business accounts:
Please send this to whoever pays your invoices. If you need a PO number on it, tell me today and I'll reissue it straight away so it doesn't get held up.
Common mistakes
- Waiting to send it. The customer's memory of a good job fades, and so does their urgency. Send it the day you finish.
- Writing "work as discussed". Anyone who wasn't there, including your customer's accounts person, has nothing to approve.
- Billing the wrong entity. Invoicing a company's manager rather than the company gives them an easy reason to send it back.
- Leaving out the deposit. If they paid $200 up front and it isn't on the invoice, the first thing you'll get is a query.
- Adding extra work with no record. A surprise line is the classic dispute. Get it approved first, using a change order.
- Only offering a check or transfer. Every extra step is a chance to put it off until tomorrow. See the options for getting paid online and what each one costs.
- Not keeping a copy. The IRS says its default retention period is 3 years, with longer periods in some cases. Other countries differ.
If you'd rather not build this in a spreadsheet, Programmable Page turns a sentence like "invoice Dana, 6 hours at $85, materials $150, $200 deposit paid" into a numbered invoice page with the sums done, a PDF and a Pay button. The Pay button needs your own Stripe account connected.
This guide is general information, not legal or tax advice. Invoice rules vary by country, state and tax status, so check with an accountant if you're unsure.
Questions
Can I send an invoice if I'm not a registered company?
Usually yes. Sole traders and freelancers invoice under their own name. In the UK, a sole trader must show their own name and any business name they use. Check your local rules on registering a trading name.
Does an invoice have to be numbered in order?
Each invoice needs a number that doesn't repeat. If you are VAT registered in the UK, HMRC asks for a sequential number. Even where it isn't required, numbering in order makes gaps and missing invoices easy to spot.
What's the difference between an invoice and a receipt?
An invoice asks for payment. A receipt confirms payment has been made. If a customer pays on the spot, a receipt alone may be enough for them, but your own records still need to show the sale.
Can I add a late fee to an invoice?
Only if it was agreed before the work, or the law gives you the right. UK businesses can claim statutory interest from other businesses. US rules vary by state, so put any fee in the quote or contract and check it's allowed.