Invoice number generator

How should I number my invoices?

Invoice numbers must be unique and, in most countries, sequential with no gaps or reused numbers. Beyond that, the format is up to you. Good formats are short, sortable and easy to read out over the phone.

Common formats

• INV-0001: a simple running sequence. Fine for most freelancers.
• INV-2026-0001: the year plus a sequence that restarts each year. Easy to file by year.
• INV-202610-001: year, month and sequence, for higher volumes.
• ACME-2026-001: a client code plus a per-client sequence. Check that your country allows per-client series.

Rules to follow

• Never reuse or skip numbers. If you cancel an invoice, issue a credit note rather than deleting it.
• Zero-pad the sequence (0042, not 42) so numbers sort correctly.
• Don't start at 1 if you'd rather not reveal you're new. Starting at 1000 is perfectly legal, as long as the numbers stay sequential from there.
• In the EU and UK, VAT rules require a unique sequential number on every VAT invoice. Several series (for example, one per year) are generally allowed.

Invoice number formula for Excel and Google Sheets

To create INV-2026-0001-style numbers that increase automatically down a column:

="INV-"&YEAR(TODAY())&"-"&TEXT(ROW()-1,"0000")

Put it in row 2 and fill down. Each row gets the next number. Note that TODAY() changes each year, so copy and paste the values once an invoice is issued.

Make the invoice too

Paste your number into the free invoice generator and download a PDF. If you're a developer, the invoice API turns JSON into invoice PDFs.