How the South Korea 개인사업자 calculator is verified

Inputs

Input	Field	Type
Annual business income after expenses (KRW)	`annualBusinessIncome`	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)
Taxable Income	`taxableIncome`	`$round($max([0, annualBusinessIncome - $const.basicDeduction]), 2)`
National income tax	`nationalTax`	`($t := taxableIncome; $round($const.r1 * $min([$t, $const.b1]) + $const.r2 * $max([0, $min([$t, $const.b2]) - $const.b1]) + $const.r3 * $max([0, $min([$t, $const.b3]) - $const.b2]) + $const.r4 * $max([0, $min([$t, $const.b4]) - $const.b3]) + $const.r5 * $max([0, $min([$t, $const.b5]) - $const.b4]) + $const.r6 * $max([0, $min([$t, $const.b6]) - $const.b5]) + $const.r7 * $max([0, $min([$t, $const.b7]) - $const.b6]) + $const.r8 * $max([0, $t - $const.b7]), 2))`
Local income tax (10% of it)	`localIncomeTax`	`$round(nationalTax * $const.localRate, 2)`
Net income / year	`netIncome`	`$round($max([0, annualBusinessIncome - nationalTax - localIncomeTax]), 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
`basicDeduction`	1500000
`localRate`	0.1
`b1`	14000000
`b2`	50000000
`b3`	88000000
`b4`	150000000
`b5`	300000000
`b6`	500000000
`b7`	1000000000
`r1`	0.06
`r2`	0.15
`r3`	0.24
`r4`	0.35
`r5`	0.38
`r6`	0.4
`r7`	0.42
`r8`	0.45

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 — 60,000,000 KRW business income — a typical full-time sole proprietor

given `annualBusinessIncome`	60000000
expect `taxableIncome`	58500000
expect `nationalTax`	8280000
expect `localIncomeTax`	828000
expect `netIncome`	50892000

Case 2 — 20,000,000 KRW — part-time

given `annualBusinessIncome`	20000000
expect `taxableIncome`	18500000
expect `nationalTax`	1515000
expect `localIncomeTax`	151500
expect `netIncome`	18333500

Case 3 — 200,000,000 KRW — into the 38% band

given `annualBusinessIncome`	200000000
expect `taxableIncome`	198500000
expect `nationalTax`	55490000
expect `localIncomeTax`	5549000
expect `netIncome`	138961000

Sources

국세청 — 종합소득세 세율 · checked 2026-08-22
2026년 종합소득세 세율·과세표준 및 지방소득세 10% · 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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