SARS requires every tax invoice in South Africa to have a unique sequential invoice number. This means each invoice must have a different number, and numbers must follow a logical sequence (no gaps or duplicates). There is no prescribed format, so you can use any numbering system as long as each invoice number is unique.
Why does SARS require sequential invoice numbers?
Unique, sequential invoice numbers serve two purposes:
- Audit trail: SARS can verify that your reported income matches the invoices you issued. Missing or duplicate numbers raise questions during an audit.
- VAT claim verification: When your client claims input VAT, SARS may cross-reference the invoice number against your records. Duplicate numbers make this impossible.
Common invoice number formats used in South Africa
| Format | Example | Notes |
|---|---|---|
| Simple sequence | INV-001, INV-002, INV-003 | The most common format. Easy to track. |
| Year prefix | 2026-001, 2026-002 | Includes year for context. Reset each year with care (see below). |
| Year-month prefix | 2026-03-001 | More granular. Useful for high-volume invoicing. |
| Client code prefix | SMITH-001, SMITH-002 | Per-client sequence. Useful if you maintain separate series per client. |
| Custom prefix | RB-001, RB-0001 | Business abbreviation. Common for branded invoice series. |
Quick answer
How should invoice numbers be formatted in South Africa?
In South Africa, SARS requires tax invoices to have a unique sequential invoice number, but does not prescribe a specific format. Common formats include a simple running sequence (INV-001, INV-002), a year prefix (2026-001), or a year-and-month prefix (2026-03-001). The most important rule is that each invoice number must be unique, and the sequence must be maintained without gaps or duplicates. If you restart your numbering each calendar year, ensure that numbers remain unique across years (for example, use a year prefix so that 2025-001 and 2026-001 are distinguishable). Invoicing software like Rebill assigns sequential numbers automatically so you never need to track them manually.
Should you restart your invoice numbers each year?
This is a common question. The answer is: only if your numbers include a year component that makes each number unique across years.
Safe: If you use year-prefixed numbers like 2025-001 and 2026-001, restarting at 001 each year is fine because the year prefix ensures no duplicates.
Risky: If you use a plain sequence (INV-001, INV-002, …), restarting at INV-001 in 2026 creates duplicates. SARS can match your 2025 INV-001 and your 2026 INV-001, which creates confusion in an audit.
The safest approach is to never restart your sequence. Let it run: INV-001 in January 2024 and INV-2,500 in March 2026. There is no requirement to reset.
Tips for managing invoice numbers
Use invoicing software. Rebill assigns invoice numbers automatically in sequence. You never have to track the next number or worry about duplicates. The system handles it.
Set your starting number deliberately. If you are switching from another system, start your Rebill sequence at the next number in your existing series. For example, if your last manual invoice was INV-042, configure Rebill to start at INV-043.
Do not skip numbers. If you create an invoice and then decide not to send it, do not delete it and reuse the number. Mark it as cancelled. SARS auditors can ask about gaps in your invoice sequence.
Do not reuse numbers. If you issued invoice INV-100 and it was later cancelled, do not reissue a new invoice as INV-100. Issue a credit note for the original and create a new invoice with the next number in sequence.
What about credit notes?
Credit notes are numbered separately from invoices. Common credit note prefixes are CN-001 or CR-001. Each credit note must reference the original invoice it is reversing. Keep your credit note sequence separate from your invoice sequence.
Frequently asked questions
Can I use any format for invoice numbers in South Africa?
Yes. SARS requires that each tax invoice has a unique sequential number, but does not prescribe a specific format. You can use any combination of letters, numbers, and separators as long as each invoice in your series has a different number and they follow a logical sequence.
What if I accidentally issued two invoices with the same number?
Issue a credit note to cancel one of the duplicate invoices and reissue it with a new, unique number. Keep clear records of which invoice was duplicated, when the credit note was issued, and what the new invoice number is. This creates an audit trail that explains the sequence to SARS if it is ever questioned.
Do quotes and invoices share the same number series?
No. Quotes and invoices are separate documents with separate number series. For example, your quotes might be QT-001, QT-002, and your invoices INV-001, INV-002. Keeping them separate avoids confusion and makes it easy to identify the document type from the reference number alone.
Does Rebill automatically assign invoice numbers?
Yes. Rebill assigns invoice numbers automatically in sequence. You can set a custom prefix (such as INV-, RB-, or your business abbreviation) and a starting number in your account settings. After that, every new invoice gets the next number in the series without any manual action from you.