How to write an invoice
An invoice has one job: to get paid without generating questions. Every field on it either helps that or gets in the way.
This guide covers what must appear, how to write each part, and the errors that most often cause an invoice to sit unpaid while both sides wait for the other.
Step 1 — Head it correctly
The document must say Invoice. Not “Bill”, not “Statement”, not your company name alone. Finance teams sort by document type, and an unlabelled document gets set aside.
Add a unique invoice number. Sequential numbering is required in most tax jurisdictions and makes your own records searchable.
Step 2 — Dates that create an obligation
Two dates, both necessary:
- Issue date — when the invoice was raised. It starts the clock and determines the tax period.
- Due date — an actual date, not “30 days”. “Due 28 February 2026” is unambiguous; “Net 30” requires the reader to calculate, and anything requiring calculation gets postponed.
Step 3 — Both parties, correctly identified
Your details: business name, address, phone, email, and tax registration number if you are registered.
Their details: the registered legal entity being billed, its address, and the contact or department. This is where invoices most often go wrong — billing a trading name instead of the registered entity, or addressing it to your project contact rather than accounts payable.
If the customer uses purchase orders, include the PO number. Some finance systems reject invoices without one automatically, and you will not be told.
Step 4 — Itemise so nobody has to ask
Each line needs a description, quantity, unit price and line total. The description is what determines whether the invoice is queried.
Weak: Consulting services — 450,000
Strong: Website redesign, phase 2 (design and build of 8 templates), as agreed 14 Jan — 450,000
The second answers the question the finance team would otherwise email you about, which typically adds a week.
Step 5 — Totals and tax
Show the arithmetic in the order a reader expects: subtotal, discount, tax, total due.
If you are registered for VAT, GST or sales tax, show it as its own line with the rate stated and include your registration number. If you are not registered, do not add tax — charging tax you cannot remit is a serious matter, not a formatting mistake.
Round consistently. If tax is calculated per line, round per line and sum; do not mix that with rounding the total, or your figures will not reconcile against the customer's.
Step 6 — Make paying easy
State exactly how to pay: bank name, account name, account number, and any reference the customer should quote — usually the invoice number.
If you accept several methods, list them. Every additional step between reading the invoice and paying it is a chance for the invoice to be set aside.
A worked example
| Field | Value |
|---|---|
| Document | INVOICE |
| Number | INV-2026-014 |
| Issue date | 3 February 2026 |
| Due date | 3 March 2026 |
| Bill to | ABC Ventures Ltd, 12 Awolowo Road, Lagos |
| Line 1 | Website redesign phase 2 — 1 × 450,000 |
| Line 2 | Hosting setup and migration — 1 × 60,000 |
| Subtotal | 510,000 |
| VAT 7.5% | 38,250 |
| Total due | 548,250 |
Mistakes that delay payment
- No due date, or a due date expressed as a term rather than a date.
- Sent to the project contact rather than accounts.
- Missing PO number where the customer requires one.
- Descriptions too vague to approve without asking.
- Payment details missing or hard to find.
- Reused or duplicated invoice numbers.
Frequently asked questions
What information is legally required on an invoice?
Requirements vary by country, but generally: the word Invoice, a unique sequential number, issue date, your business name and address, the customer's details, a description of goods or services, the amount due, and your tax registration number and tax shown separately if registered.
How do I number invoices?
Uniquely and sequentially. INV-2026-001 works well — it sorts correctly, shows the year and resets cleanly. Never reuse or delete a number.
Should I write Net 30 or an actual due date?
An actual date. Net 30 requires the reader to calculate, and anything requiring calculation gets postponed. Due 3 March 2026 is unambiguous.
What do I do if I made a mistake on a sent invoice?
Issue a credit note or a corrected invoice with a new number that references the original. Do not silently edit and resend — that leaves two different documents sharing one number.
Do I need to charge tax on my invoice?
Only if you are registered for VAT, GST or sales tax. If you are, show it separately with the rate and your registration number. If you are not registered, do not add tax you cannot remit.
How detailed should line descriptions be?
Detailed enough that someone who was not in the meeting can approve it without asking you a question. Every query adds days to payment.