VAT calculator (South Africa)

Adding VAT is the easy direction: multiply by 15% and add it on, so R100 excluding VAT becomes R15 of VAT and R115 including it. Going backwards is where people slip. To get the VAT out of a VAT-inclusive price you do not take 15% of it — that would give R17,25 on a R115 invoice, which is wrong. The inclusive amount is 115% of the original, so the amount excluding VAT is the inclusive amount multiplied by 100/115, and the VAT is whatever is left over. On R115 that is R100 excluding VAT and R15 of VAT, which is the answer you started with.

The shortcut worth remembering is that VAT is 15/115 of a VAT-inclusive price, which is roughly 13,04% of it. If someone quotes you an inclusive figure and you need the ex-VAT number in your head, divide by 1,15.

South African VAT has been 15% since 1 April 2018, when it rose from the 14% it had sat at since 1993. In 2025 that nearly changed. The February budget was postponed — itself unprecedented — and the version tabled in March proposed lifting VAT by half a percentage point to 15,5% on 1 May 2025, with another half point to follow in 2026. It was withdrawn in late April after a court challenge and a fair amount of political arithmetic, and the rate stayed at 15% without ever actually changing.

A number of accounting systems had already been reconfigured for 15,5% by then, which is the sort of thing that produces reconciliation work for months afterwards. This calculator holds the rate in a single named constant with that history noted next to it, so a future change is one edit rather than a hunt through the file.

Money and floating-point numbers get along badly. In JavaScript — and in most languages — 0.1 + 0.2 is 0.30000000000000004, because binary fractions cannot represent a tenth exactly. Do enough of that on invoice lines and you eventually get a total that is a cent out from the sum of its parts, which is exactly the kind of discrepancy that costs somebody an afternoon.

So this calculator never holds an amount as a fraction. Your input is parsed straight into a whole number of cents from the characters you typed, all the arithmetic is integer arithmetic, and rounding is an explicit round-half-up rather than whatever the language does by default. The VAT line when extracting is calculated as the inclusive amount minus the ex-VAT amount rather than rounded on its own, which guarantees the three figures you see always add up. Open the page source if you want to see it — the script is right there, unminified.

One honest caveat: this is a calculator, not a tax opinion. SARS has rules about which of these figures rounds where on an actual tax invoice, and about zero-rated and exempt supplies that no calculator can infer from a single number. Check with your accountant before relying on it for anything you have to sign.