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Invoice number generator

Choose a format for your invoice numbers (prefix, year or month, client code, how many digits) and get the numbers to use, ready to copy. Already invoicing? Type your last invoice number and get the next one. Nothing you type leaves your browser.

Quick start:

What comes next?

Type it exactly as it was printed. The page adds one to the last run of digits and keeps the zeros.

Your format

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Pattern:

What comes next?

Type your last invoice number on the left.

What makes a good invoice number

  1. Unique. No two invoices share a number, ever. That is the one rule nearly every tax office and accounts team agrees on.
  2. Sequential. Each invoice is the last one plus one. A clean run makes a missing or duplicated invoice easy to spot, for you and for anyone checking your books.
  3. One series per document type. Quotes, proforma invoices, credit notes and receipts get their own prefixes (QUO, PRO, CN, RCP), so they don't use up or break your invoice numbers.
  4. Never reused. If an invoice is cancelled, its number stays used: issue a credit note instead of deleting it or giving the number to a new invoice.
  5. Easy to read out and search. Short, no spaces, and the same length each time (that is what the leading zeros are for).

Common formats

FormatExampleGood for
Prefix + counterINV-0042Simplest. Keep counting up for years.
Prefix + year + counterINV-2026-0042Shows the year at a glance; you can restart at 0001 each January.
Year + counter2026-042Short, no prefix. Fine if you send few other documents.
Prefix + year + month + counterINV-2610-007Monthly billing; the date part tells you when it was issued.
Prefix + client code + counterINV-ACME-012Clients who want their own run of numbers. Keep a list of codes, and make sure two clients never share one.

The client-code style gives each client a separate series. If your tax office expects one sequence for all your invoices, use a single series instead and put the client in the invoice itself.

What the rules say (UK example)

Rules differ by country. In the UK, gov.uk says an invoice must include "a unique identification number", and HMRC's VAT guide (Notice 700, section 16.3) asks VAT-registered businesses for "a sequential number based on one or more series which uniquely identifies the document" (both checked 17 October 2026). Check what applies where you are registered. This page is not legal or tax advice.

Changing your format

You can switch to a new format at any time, for example at the start of a year. Don't renumber invoices you already sent; start the new format from the next invoice, and note the last old number somewhere so the jump is easy to explain.

Let the app count for you

In the free Kitebill app you enter the prefix and the next number once, under Settings. Every new invoice then gets the next number, padded to 4 digits, and Duplicate turns last month's invoice into this month's with a new number. If you type a higher number yourself, the app carries on from there. It doesn't change the year in the prefix by itself, so update it each January if your numbers include the year. Your data stays in your browser. Free for 3 clients and 10 invoices; Pro is US$29 once.

Making one invoice now? The free invoice generator takes the number you choose here. For the other documents: quotes, proforma invoices, credit notes and receipts.

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Questions

How do I number my invoices?

Pick one format and stick to it: a prefix, optionally the year, and a counter that goes up by one for every invoice, for example INV-2026-0001, INV-2026-0002. Each number is used once and never reused, even if the invoice is cancelled. This page builds the format and lists the numbers; type your last number into What comes next? to get the next one.

Do invoice numbers have to be sequential?

For VAT-registered businesses in the UK, yes: HMRC’s VAT guide asks for "a sequential number based on one or more series which uniquely identifies the document". For other UK invoices gov.uk asks for "a unique identification number". Other countries have their own rules, so check yours. A plain counter that never skips or repeats keeps you safe almost everywhere. This is not legal or tax advice.

Should invoice numbers restart every year?

You can. With the year in the number (INV-2026-0042), starting again at INV-2027-0001 in January keeps every number unique, because the year is part of it. Without the year in the number, keep counting up instead of restarting, or you will get duplicates.

What do I do with the number of a cancelled invoice?

Leave it used. Don’t give the same number to a new invoice and don’t delete the old one; issue a credit note that cancels it. That way the series has no gaps and no duplicates.

Should quotes and credit notes share the invoice numbers?

Usually not. Give each document type its own series, such as QUO-0001 for quotes, PRO-0001 for proforma invoices, CN-0001 for credit notes and RCP-0001 for receipts, so your invoice series stays unbroken.

Does Kitebill number invoices for me?

Yes. In the free Kitebill app you set an invoice prefix and the next number once (Settings), and every new invoice gets the next number, padded to 4 digits (INV-0001). Duplicate also takes the next number. The app does not change the year in the prefix by itself: each January, update the prefix (for example to INV-2027-) and set the next number to 1 if you restart yearly.