Invoice numbers need to do two things: be unique, and run in order with no gaps. Beyond that, the format is up to you.
Formats that work
| Format | Example |
|---|---|
| Plain sequence | INV-0001, INV-0002 |
| Year and sequence | 2026-001, 2026-002 |
| Client code and sequence | ACME-014 |
A plain sequence is the easiest to keep straight. Adding the year helps when you look back through old records. Client codes are useful if you send one client many invoices, but you then have a separate sequence to manage for each client.
Rules worth keeping
- Never reuse a number. If an invoice was wrong, correct it with a credit note or a new invoice. Do not hand its number to something else.
- Do not skip numbers. Gaps make your accountant, and tax inspectors, wonder what is missing.
- Use leading zeros. INV-0009 and INV-0010 sort correctly in a folder. INV-9 and INV-10 do not.
- You do not have to start at 1. Starting at 1001 or 0100 is fine if you would prefer not to advertise that this is your first invoice.
Let the numbering look after itself
The invoice generator remembers your last number and adds one for each new invoice. Type your first number in whatever format you like and it will follow the pattern, so 2026-041 is followed by 2026-042.