How the South Africa vat calculator is verified

Inputs

Input	Field	Type
Amount	`amount`	number
Direction	`direction`	string
Taxable supplies per annum	`annualTurnover`	number
B2B reverse charge applies	`reverseCharge`	boolean

The formula

Each derived value below is computed by the Valem engine from the expression shown, in this order. Nothing else runs — there is no hidden code path.

Derived value	Field	Formula (JSONata)
Rate	`rate`	`$const.standardRate`
Effective Rate	`effectiveRate`	`reverseCharge ? 0 : rate`
Net Amount	`netAmount`	`direction = 'remove' ? $round(amount / (1 + effectiveRate), 2) : $round(amount, 2)`
Vat Amount	`vatAmount`	`$round(netAmount * effectiveRate, 2)`
Gross Amount	`grossAmount`	`$round(netAmount + vatAmount, 2)`
Must Register	`mustRegister`	`annualTurnover > $const.registrationThreshold`
Registration Status	`registrationStatus`	`annualTurnover > $const.registrationThreshold ? 'required' : annualTurnover > $const.registrationThresholdVoluntary ? 'optional' : 'not available'`

Rates and thresholds

The expressions above read these as $const. They are the figures the annual refresh replaces, so they live as data rather than being written into the formulas — which is what makes a year-on-year change a one-line diff instead of an edit to arithmetic.

Constant	Value
`standardRate`	0.15
`registrationThreshold`	2300000
`registrationThresholdVoluntary`	120000

Test vectors (7)

Every case is executed against this model on each build, by the Java engine and independently by a JavaScript one. A mismatch of a single cent fails the build, so the page cannot ship advertising a figure the model no longer produces.

Case 1 — S1 100.00 ZAR net at 15%

given `amount`	100
given `direction`	add
given `reverseCharge`	no
given `annualTurnover`	0
expect `vatAmount`	15
expect `grossAmount`	115
expect `netAmount`	100

Case 2 — S2 115.00 ZAR gross back to net

given `amount`	115
given `direction`	remove
given `reverseCharge`	no
given `annualTurnover`	0
expect `netAmount`	100
expect `vatAmount`	15

Case 3 — S3 reverse charge: the supplier charges no VAT

given `amount`	100
given `direction`	add
given `reverseCharge`	yes
given `annualTurnover`	0
expect `vatAmount`	0
expect `grossAmount`	100

Case 4 — S4 above R2.3 million: registration is compulsory

given `amount`	100
given `direction`	add
given `reverseCharge`	no
given `annualTurnover`	3000000
expect `mustRegister`	true
expect `registrationStatus`	required

Case 5 — S5 between R120 000 and R2.3 million: voluntary

given `amount`	100
given `direction`	add
given `reverseCharge`	no
given `annualTurnover`	800000
expect `mustRegister`	false
expect `registrationStatus`	optional

Case 6 — S6 R1.5 million would have been compulsory before 1 April 2026, and is not now

given `amount`	100
given `direction`	add
given `reverseCharge`	no
given `annualTurnover`	1500000
expect `mustRegister`	false
expect `registrationStatus`	optional

Case 7 — S7 below R120 000: registration is not available

given `amount`	100
given `direction`	add
given `reverseCharge`	no
given `annualTurnover`	90000
expect `mustRegister`	false
expect `registrationStatus`	not available

Sources

SARS - Value-Added Tax: standard rate of 15% · checked 2026-10-05
SARS - Value-Added Tax, What is new? (25 Feb 2026): R2.3m compulsory / R120 000 voluntary from 1 April 2026 · checked 2026-10-05
SARS FAQ - the new threshold for VAT registration (R2.3 million) · checked 2026-10-05

Check it yourself — and reuse it

The whole model as JSON — inputs, outputs, formulas, vectors and sources in one re-runnable document.

This model is published under CC BY 4.0: use it, adapt it, build on it, with attribution. The licence covers the model — the expression of each rule and the arrangement of the catalog. The rates and thresholds are law, and nobody licenses those; the sources above are where they come from.

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