Invoice Numbering Rules in South Africa: What SARS Requires

The rule is shorter than most people expect. A VAT invoice needs its own serial number, nobody else's invoice can share it, and the numbers should run in order so you can account for every one. Everything else, the prefix, the padding, whether you restart each year, is your choice. This article covers the one line of law that matters, the habits that keep you out of trouble, and how SortedNexus numbers invoices.

What the VAT Act says about invoice numbers

Section 20(4) of the Value-Added Tax Act lists what a full tax invoice must contain. Item (d) asks for "an individual serialized number and the date upon which the tax invoice is issued". That is the whole numbering rule. The Act does not prescribe a format, a length or a prefix, so INV-0001, 2026/014 and ACME-0042 are all equally valid.

Two words in that line do the work. Individual means each invoice has its own number, and no two invoices you issue share one. Serialized means the numbers belong to a series, one after another, rather than being picked at random. The Act does not say "gap-free" in so many words, and we are not aware of a SARS ruling that defines the term further, so read what follows as our practical reading and not a quote from the law. It is the reading that is easiest to defend, because a series with missing numbers invites the question of what happened to them.

The rule applies to tax invoices, issued by VAT-registered vendors. If you are not registered, SARS does not set a numbering rule for your invoices. You should still number them the same way, because your clients' accounts departments, your own records and any later audit all work better with a clean series. If you are unsure which document you should be issuing, our guide to VAT invoice requirements lists every item on a tax invoice.

A numbering scheme that holds up

A simple prefix plus a padded counter covers almost every small business. A few habits make it hold up over years:

Let one system hand out the numbers. The usual way a series breaks is two sources of numbers, such as a spreadsheet and an invoicing tool, or a business partner who keeps a separate list. Pick one and use only that.
Never reuse a number. Even if you throw away a draft nobody saw, do not hand its number to the next invoice unless you are certain it never left your hands.
Do not change a number after you have sent the invoice. Your client has already quoted it in their records and possibly in a payment.
Keep a separate series for each business. If you run more than one business, each is its own supplier, so each gets its own sequence. We cover running several from one account in our article on multiple businesses.
Use a prefix if you ever expect to change systems. A year or business code in the prefix makes it obvious where one series ended and the next began.

Padding the counter with zeros (0001 rather than 1) is purely cosmetic, but it keeps invoices sorting correctly in a spreadsheet or a bank statement export.

Cancelled invoices and mistakes: do not delete, do not renumber

This is where most numbering problems start. You issue an invoice, then find it is wrong, or the job is called off. The tempting fix is to delete it and carry on, which leaves a hole in your series. The better fix is to keep the original on file and mark it cancelled, so every number is still accounted for and the record shows what happened.

What you then do depends on the mistake:

An error in the particulars. A wrong address or a missing line on a tax invoice can be corrected. Section 20 deals with this, and it expects you to keep information that links the corrected invoice to the original. It also says you should not issue more than one tax invoice for the same supply, which is why you correct the invoice and do not simply raise a second one.
A change after the invoice was issued. A price adjustment, a return or a cancelled supply is handled with a credit note or debit note under section 21, not by rewriting the original. Give credit notes their own numbers in their own series.
An invoice nobody ever received. If it truly never left your system, a cancellation on file is still the cleanest record.

The rules for corrections and credit notes have their own detail, and this article is only about numbering. For anything specific, such as a large correction or a VAT period that has already been submitted, confirm the treatment with your accountant.

How SortedNexus numbers your invoices

We built numbering around the habits above, so you do not have to remember them.

One source of numbers. When you save an invoice from an account, we assign the next number in your series, in the form INV-0001, INV-0002 and so on. There is no number field to type into, so two invoices cannot end up with the same number by accident.
One series per business. If you use the Pro plan with extra businesses, each business has its own INV-0001 sequence, matching how each is a separate supplier.
Cancel, do not delete. An invoice that goes wrong is marked cancelled and stays in your list with its number and its history. The invoice pages have no delete button, so a cancelled number stays accounted for.
Quotes have their own series. They are numbered QUO-0001 onwards, separate from invoices, and converting a quote to an invoice gives the invoice the next invoice number. We wrote about keeping the two linked in quoting and invoice record keeping.

What this does not do

The free invoice builder, which needs no account, cannot keep a series, because nothing is saved. Each invoice gets a number built from the time you created it, such as INV-1791561185438. That is unique, which suits a one-off invoice, but it is not a sequence, so if you invoice regularly, sign up and let the numbers run in order. SortedNexus also does not yet issue credit notes. A cancelled invoice stays on record, but if you need a credit note, for example for a VAT period you have already filed, confirm with your accountant how to produce one. And it cannot start your series at a number you choose, which matters if you are moving over from another tool partway through a year. In that case the new series starts at INV-0001and you keep the old tool's records for the earlier invoices.

Numbers that take care of themselves

Create an invoice and the next number is already assigned. Start with the free builder, or create an account to keep every invoice in one numbered series.

Create an invoice →See pricing

Sources

Disclaimer: This article is general information about invoice numbering and about how SortedNexus numbers invoices. Where it describes how a rule works in practice, that is our reading and not a SARS ruling. It is not tax, accounting, or legal advice, and it does not replace advice from a qualified accountant.

Invoice numbering rules in South Africa: what SARS actually requires