Invoice Number Generator
Enter a prefix and starting number to preview professional invoice number formats and copy your next sequence.
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This free invoice number generator turns a prefix and a starting number into clean, professional invoice numbers. Pick the format that suits your business, then copy the next numbers in the sequence straight into your records or invoicing tool.
Why invoice numbers matter. Every invoice needs a unique identifier so you and your client can reference it, match it to a payment, and keep your bookkeeping tidy. In many countries invoice numbers must also be sequential with no gaps, which makes your records complete and easy to audit.
The four formats above. Sequential (INV-0001) is the simplest and works for any business. Year-based (INV-2026-0001) groups invoices by year and is handy to reset each January. Year-and-month (INV-2026-07-0001) adds the month for higher volumes. Client-prefixed (INV-ACME-0001) embeds a short client code so you can spot who an invoice belongs to at a glance.
Whichever you choose, stay consistent: keep the same pattern, increase the number by one for each invoice, and never reuse a number. Consistent numbering keeps your accounts clean and makes chasing payments far easier.
Frequently asked questions
What is a good invoice number format?
A good format is unique, sequential, and easy to sort. Popular choices are a simple sequence like INV-0001, a year-based format like INV-2026-0001, a year-and-month format like INV-2026-07-0001, or a client-prefixed format like INV-ACME-0001. Pick one and keep it consistent so every invoice is easy to reference.
Do invoice numbers have to be sequential?
In many countries — and for clean bookkeeping everywhere — invoice numbers should be sequential with no gaps, so your records are complete and auditable. Sequential numbering also makes it obvious if an invoice is missing. Resetting the sequence each year (for example starting again at 0001) is fine as long as the year is part of the number.
Can invoice numbers have letters?
Yes. Letters and separators such as a prefix (INV), a year, or a short client code are commonly used to keep numbers organised and human-readable. The only rule that matters is that each invoice number is unique and follows a consistent, sequential pattern.
What number should I start my invoices at?
You can start anywhere. Many businesses begin at 0001, while others start at a higher number such as 1000 so their first invoices do not signal that they are brand new. Whatever you choose, increase by one for each invoice and never reuse a number.