Free Invoice Number Generator

How the formula builds each number

A list gets you through the next ten invoices. The formula keeps going after that, in the same row as the invoice it numbers. Here's the default, INV-2026-0001, taken apart.

In Google Sheets and Excel, ROW() is the number of the row the formula sits in, so the counter needs no column of its own. If your first invoice should be 1001, the formula adds 999 instead of subtracting 1. If you pick year and month in the generator, the formula also adds the month as two digits, as in INV-202601-0001.

Airtable formulas can't read a row number, so the count comes from an Autonumber field, which gives each new record the next number. REPT and LEN add the zeros, and DATETIME_FORMAT writes the year from your date field. When a number outgrows its digits, both formulas print it in full: invoice 10,000 with four digits is INV-2026-10000, not INV-2026-0000.

Never delete or sort an invoice you've sent

Because the Sheets and Excel formula counts rows, deleting a row or sorting the sheet gives every invoice below it a new number, including invoices your clients already have. When an invoice is cancelled, keep its row and mark it Void. Airtable works the other way: when you delete a record, the remaining records are not renumbered, so you'll see a gap where it was.

Worked example: numbering invoices in a Google Sheet

A studio keeps one row per invoice: the date in column A, the number in column B, then the client and a status. In B2 they paste the default formula and fill it down the column. Every row gets the next number, and the year comes from that row's date.

The Blue Fern invoice was cancelled after it went out, so its row stays and says Void. Had the studio deleted row 3, Northwind's invoice would slide up to row 3 and turn into INV-2026-0002 in the sheet, while the PDF in Northwind's inbox still says INV-2026-0003.

What the rules say about invoice numbers

In the UK, every invoice must include "a unique identification number". For VAT invoices, the EU VAT Directive asks for "a sequential number, based on one or more series, which uniquely identifies the invoice", and HMRC asks for a sequential number based on one or more series on UK VAT invoices. One or more series means you can start a new series each year, with the year in the number, or keep one count running from year to year. Either way, no number is used twice. This is a summary, not legal or tax advice.