How to Create an Invoice: Every Field Explained (With Examples)

An invoice is more than a request for payment. It's a legal record of a sale, the document your customer's accounts team needs before they can pay you, and an entry in your own books. Get it right and you get paid faster with fewer emails. This guide goes through every field an invoice needs and explains what happens in your bookkeeping when you send one.

The fields every invoice needs

Requirements vary by country, so check your local tax authority's guidance. In the UK, GOV.UK's guidance on invoicing sets out the essentials below.

1. The word "Invoice" and a unique number

Make it obvious the document is an invoice, and give each one a unique, sequential number such as INV-0042. Numbers let both sides refer to it, match payments to it and keep records in order. Never reuse a number. If an invoice is cancelled, void it and keep it on file.

2. Your business details

Your business name, address and contact details. Limited companies should use their full registered name. If you're VAT-registered, include your VAT number.

3. Your customer's details

Their business name and address, and ideally a named contact or purchase-order number. Many larger companies won't pay an invoice without their PO number on it.

4. Invoice date and supply date

The invoice date is when you issue it. The supply date (or tax point) is when the goods or service were delivered. They're often the same, but not always.

5. Line items

Describe each item clearly enough that the person approving payment knows what it is:

Vague lines like "work as discussed" invite questions, and questions delay payment.

6. Subtotal, tax and total

Show the subtotal before tax, the tax amount and rate, and the total due. For example: subtotal £1,200.00, VAT at 20% £240.00, total £1,440.00.

7. Due date and payment terms

State the actual due date ("Due 1 December"), not just "30 days". Include how to pay: bank details, a payment link or both.

8. Notes (optional)

A thank-you, late-payment terms or a reference for the payment. Keep it short.

What happens in your books when you send an invoice

In double-entry bookkeeping, posting an invoice records two things at once:

• Your customer now owes you the total, so accounts receivable goes up by £1,440.
• You've earned income and collected tax, so sales goes up by £1,200 and VAT payable by £240.

When the customer pays, the receivable clears into your bank account. If you're new to this, see double-entry bookkeeping explained.

Part payments

If a customer pays £500 of £1,440, record the £500 against the invoice. The balance due becomes £940 and the invoice shows as part paid until the rest arrives.

Voiding vs deleting

A draft invoice that was never sent can be deleted. A posted invoice should be voided: it stays in your records, marked void, and its effect on the books is reversed. That keeps your numbering and history intact.

Six ways to get paid faster

1. Invoice immediately when the work is delivered, not at month end.
2. Use clear line items so approvers don't need to ask questions.
3. Include PO numbers for larger customers.
4. Offer an easy way to pay, such as a payment link alongside bank details.
5. Set shorter terms where your relationship allows it.
6. Follow up on schedule. An aging report shows exactly who to chase.

Common invoice mistakes

• Missing or duplicated invoice numbers
• No due date, or only "net 30"
• VAT included in the price but not shown separately (if you're registered)
• The wrong legal name for the customer's company
• Editing a sent invoice instead of issuing a credit note or voiding it

Creating invoices in Zelvorm Books

Zelvorm Books numbers invoices automatically, calculates tax, and posts the journal for you when you post the invoice. Record part payments and the balance due keeps itself up to date; void cleanly when you need to. It's free double-entry bookkeeping for small businesses.

Invoice numbering that scales

A good numbering system is simple, sequential and never reused:

• Simple sequence: INV-0001, INV-0002, INV-0003. Works for most small businesses.
• Year prefix: 2026-0001, 2026-0002, restarting each year. Useful if you invoice a lot.
• Customer prefix: NW-001 for Northwind. Can help with many repeat customers, but makes the overall sequence harder to audit.

Whatever you choose, keep one sequence per business, and let your software assign numbers so there are no gaps or duplicates.

Credit notes: correcting an invoice

Once an invoice has been sent, don't edit it. If the amount was wrong or the customer returns something, issue a credit note: a document that reduces what the customer owes, referencing the original invoice number. Then, if needed, issue a new, correct invoice.

In your books, a credit note is the opposite of an invoice: it reduces accounts receivable, sales and any tax charged. If the whole invoice was a mistake, voiding it does the same job in one step.

Deposits and staged invoices

For larger jobs, invoicing in stages protects your cash flow:

Each stage gets its own invoice and number, with a description that makes the stage clear ("Deposit: 40% of website project, quote Q-0112"). Agree the schedule in writing before you start.

Invoicing customers in other currencies

If you invoice overseas customers in their currency:

• Show the currency clearly on every amount (USD, EUR).
• Decide who pays bank and conversion fees, and say so.
• Record the payment in your own currency when it arrives; any difference from the invoiced value is a foreign-exchange gain or loss.

Your accountant can advise on how to treat exchange differences for tax.

A simple invoice template

Late payment: know your terms

Put your late-payment terms on the invoice and in your contract. In the UK, businesses can claim statutory interest and fixed compensation on late commercial payments; GOV.UK explains the rules. Simply stating your terms often speeds up payment. For a full follow-up routine, see our guide to accounts receivable aging.

The short version

A good invoice has a unique number, both parties' details, clear line items, tax shown separately, an exact due date and simple payment instructions. Send it promptly, record it properly, and chase it on a schedule.