How the Singapore self-employed calculator is verified

Inputs

Input	Field	Type
Annual net trade income (SGD)	`netTradeIncome`	number

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)
MediSave contribution	`medisave`	`$round(netTradeIncome <= $const.medisaveFloor ? 0 : netTradeIncome * $const.medisaveRate, 2)`
Income tax	`incomeTax`	($i := netTradeIncome; $round($const.r2 * $max([0, $min([$i, $const.b2]) - $const.b1]) + $const.r3 * $max([0, $min([$i, $const.b3]) - $const.b2]) + $const.r4 * $max([0, $min([$i, $const.b4]) - $const.b3]) + $const.r5 * $max([0, $min([$i, $const.b5]) - $const.b4]) + $const.r6 * $max([0, $min([$i, $const.b6]) - $const.b5]) + $const.r7 * $max([0, $min([$i, $const.b7]) - $const.b6]) + $const.r8 * $max([0, $min([$i, $const.b8]) - $const.b7]) + $const.r9 * $max([0, $min([$i, $const.b9]) - $const.b8]) + $const.r10 * $max([0, $min([$i, $const.b10]) - $const.b9]) + $const.r11 * $max([0, $min([$i, $const.b11]) - $const.b10]) + $const.r12 * $max([0, $min([$i, $const.b12]) - $const.b11]) + $const.r13 * $max([0, $i - $const.b12]), 2))
Net income / year	`netIncome`	`$round($max([0, netTradeIncome - medisave - incomeTax]), 2)`

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
`medisaveRate`	0.08
`medisaveFloor`	6000
`b1`	20000
`b2`	30000
`b3`	40000
`b4`	80000
`b5`	120000
`b6`	160000
`b7`	200000
`b8`	240000
`b9`	280000
`b10`	320000
`b11`	500000
`b12`	1000000
`r2`	0.02
`r3`	0.035
`r4`	0.07
`r5`	0.115
`r6`	0.15
`r7`	0.18
`r8`	0.19
`r9`	0.195
`r10`	0.2
`r11`	0.22
`r12`	0.23
`r13`	0.24

Test vectors (3)

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 — 90,000 SGD net trade income — a typical full-time freelancer

given `netTradeIncome`	90000
expect `medisave`	7200
expect `incomeTax`	4500
expect `netIncome`	78300

Case 2 — 35,000 SGD — part-time

given `netTradeIncome`	35000
expect `medisave`	2800
expect `incomeTax`	375
expect `netIncome`	31825

Case 3 — 250,000 SGD — a well-paid consultant

given `netTradeIncome`	250000
expect `medisave`	20000
expect `incomeTax`	30700
expect `netIncome`	199300

Sources

IRAS — Individual income tax rates for residents · checked 2026-08-22
CPF — MediSave contributions for self-employed persons · checked 2026-08-22

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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