Use a prefix and a zero-padded counter (INV-0001) or a year-based format (2026-0001), never skip or reuse a number, keep quotations and credit notes in their own series, and cancel rather than delete an issued invoice. SARS requires each tax invoice to carry an individual serialised number.
The rules
- Unique: no two invoices share a number, ever.
- Sequential: gaps look like missing income to an auditor. If you cancel an invoice, keep the number and mark it cancelled.
- Fixed once issued: never renumber sent invoices.
- Separate series for quotations (QUO), credit notes (CN) and, if you run several brands, per brand.
Formats that work
| Format | Example | Good for |
|---|---|---|
| Prefix + counter | INV-0042 | Most small businesses |
| Year + counter | 2026-0042 | Easy year-end filing |
| Year-month + counter | 2026-09-004 | High volume, monthly reconciliation |
| Client code + counter | ACME-0007 | A handful of large clients |
Starting number
You do not have to start at 1. Starting at 1001 hides how new you are; nobody will judge you either way. If you are switching software, continue from your last number so the series stays unbroken.
Custom numbering in InvoiceWriteNow
Starter and Pro use INV-0001 style numbering, allocated automatically so two people can never issue the same number. The Business plan lets you set your own prefix, padding and starting number for invoices and quotations separately.
Numbering handled, every time.
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