Foreign Worker Flat Tax (19%) Calculator

A foreign national working in Korea can pay income tax one of two ways. The first is normal taxation, exactly as a Korean employee would: subtract deductions, apply the progressive rates. The second is the flat rate, which multiplies gross pay by 19% and stops there. This calculator feeds the same salary and the same deductions into both methods, puts the totals side by side, tells you which one is cheaper and by how much, and works out the salary at which the answer flips.

There are four inputs: annual gross pay, the number of people you can claim under the basic deduction (yourself included), other income deductions such as pension and health insurance contributions or card spending, and other tax credits such as medical expenses or pension savings. The last three only matter under normal taxation. The flat rate ignores every one of them, which is why adding deductions pulls the normal-tax figure down while the flat-rate figure does not move at all.

The first person who should run this is anyone whose employer has said, on joining, "you are a foreigner, so sign the 19% flat-rate application." The rate looks low on paper, but the flat rate is an election you have to apply for, not a default. Checking both methods against your own salary before signing avoids a costly mistake.

Anyone already on the flat rate should also recheck every year. The election is made per tax period, so a pay rise or a new dependant can move the better option. In a year when you marry, have a child, or start a housing subscription account or pension savings plan, the deductions on the normal-tax side grow and the crossover salary climbs with them.

The flat rate comes from 조세특례제한법 제18조의2. Up to the tax period ending within 20 years of the day you first started working in Korea, employment income may be taxed at 19% instead of the progressive rates. In exchange, the same article states that no exemptions, income deductions, reductions or tax credits apply. The calculation is two lines: gross pay times 19% gives the income tax, and 10% of that is added as local income tax.

Normal taxation follows the sequence in 소득세법. Start with gross pay, subtract the employment income deduction (소득세법 제47조), then ₩1,500,000 per person under the basic deduction and any other income deductions, which gives the tax base. Apply the progressive rates in 제55조 to get the calculated tax, subtract the employment income tax credit (제59조) and any other credits to reach the income tax, and add 10% local income tax. The calculator compares the two totals and calls the lower one the better deal. It then holds your deductions fixed and raises gross pay until the two totals meet, and reports that salary as the crossover point.

Take someone earning ₩50 million a year, claiming only themselves, with ₩3 million of income deductions from social insurance contributions. Under the flat rate, 19% of ₩50 million is ₩9.5 million of income tax, plus ₩950,000 local income tax, for ₩10.45 million in total. Under normal taxation, the employment income deduction of ₩12.25 million, the basic deduction of ₩1,500,000 and the other ₩3 million come off first, leaving a tax base of ₩33.25 million. The calculated tax on that is ₩3,727,500; after the employment income tax credit of ₩660,000 the income tax is ₩3,067,500, and with local income tax the total is ₩3,374,250.

The gap is ₩7,075,750. Choosing the flat rate on the strength of the headline number would cost that much every year. On the same deductions, gross pay has to pass roughly ₩141.7 million before the flat rate starts to win, and every additional dependant or deduction pushes that line higher.

The biggest is believing that 19% must be a bargain because it is lower than the top progressive rates. Under normal taxation the rates apply to the tax base, not to gross pay, and the tax base is what is left after every deduction. The effective rate, meaning tax actually paid divided by gross pay, stays well under 19% across the middle of the salary range. In the example above, the normal-tax effective rate is in single digits.

The second is electing the flat rate and then collecting medical and card receipts for the year-end settlement. None of it counts under the flat rate, so the effort is wasted. The third is forgetting the time limit: 20 years after your first working day the flat rate ends and you return to normal taxation. Finally, the treatment only applies if you apply for it. If the numbers say the flat rate wins, file the application with your employer; if they say it loses, simply do not.