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How to number your invoices
An invoice number lets you and your client refer to one specific invoice. The two rules that matter most: every number is unique, and numbers go up in order.
Common formats
| Format | Example | Good for |
|---|---|---|
| Simple sequence | INV-0001, INV-0002 | Most small businesses |
| Year + sequence | 2026-001, 2026-002 | Seeing at a glance which year an invoice belongs to |
| Client code + sequence | ACME-001 | A few large clients you invoice often |
Tips
- Pad numbers with zeros (0001) so they sort correctly in file lists and spreadsheets.
- Don't reuse a number, even if an invoice was cancelled — keep the cancelled invoice in your records instead.
- Use a different prefix for estimates (EST-) and receipts (RCPT-), so they never clash with invoice numbers.
- If you are new and prefer not to start at 0001, you can start at a higher number; just keep counting up from there.
How Slipfold numbers documents
Slipfold suggests the next number automatically by adding one to your most recent invoice (INV-0009 → INV-0010), keeping your prefix and zero padding. If you type your own number, the next invoice continues from it. Estimates and receipts have their own sequences.
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Create an invoiceThis page is general information, not tax, legal or accounting advice. Rules differ by state and country — check with your state revenue department or a qualified professional.