Check Whether You Will Get a November Interim Income Tax Notice If You Have Side-Job Income

What is comprehensive income tax interim prepayment?

The National Tax Service describes interim prepayment not as collecting next May's tax in advance, but as a system where you pay in November the income tax on this year's first-half (January 1 to June 30) income. The timing differs from the comprehensive income tax filing in May, and the key point is that if your side-job income counts as business income, you may get a notice in November.

The amount is calculated by the National Tax Service from the prior tax period's data and sent as a notice in early November. The formula is one-half of the interim prepayment base amount, minus the tax on gains from selling land and the like that you made a preliminary filing for and paid in the first half. The base amount is the interim prepayment you paid in November of last year, plus the tax you paid voluntarily in the May-June final filing, additional tax paid, and tax paid on late filings, minus any refund.

Who is excluded for people with side jobs?

The groups the National Tax Service lists as excluded are as follows.

What to notice in this list is that you are excluded if you have only wage or other income. If, besides your company salary, you received only a one-time lecture fee, it is other income and may not apply. On the other hand, business income received repeatedly, like delivery or ordinary lectures, was not named among the exclusions in the guidance I opened. Even for the same 3.3% income, it can differ by line of business and by whether year-end tax settlement applies, so if you got a notice or have doubts, it is safer to check with the National Tax Service call center at 126.

How low is low enough to skip paying?

If the interim prepayment is under 500,000 won, you do not pay it, under the de minimis non-collection rule. If your side job was small and last year's tax was small, you may not get a notice at all. Conversely, if it is 500,000 won or more and you are not in an excluded group, you must pay within the notice's deadline. If your first-half results this year dropped sharply, look first at the estimated amount filing just below.

What if your income dropped this year?

The notice is calculated from last year's results, so the amount comes out the same even if this year's first half went worse. The mechanism for such cases is the interim prepayment estimated amount filing. If the estimated amount calculated from first-half comprehensive income is less than 30% of the interim prepayment base amount, you can file and pay using the estimated amount.

The order of calculating the estimated amount, as stated by the National Tax Service, is as follows.

1. Multiply first-half comprehensive income by 2, then subtract carried-over losses and the comprehensive income deduction to get the tax base.
2. Multiply the tax base by the basic tax rates (6% to 45%) to get the calculated tax.
3. Divide the calculated tax by 2, then subtract deductions, exemptions, withholding tax, and the like that arose by June 30.

The basic rates rise from 6% for a tax base up to 14 million won, to 15% up to 50 million won, 24% up to 88 million won, and 35% up to 150 million won. The deadline to submit the filing and pay voluntarily is November 30, 2026, the same as for the notified amount.

One point is easy to miss. Even if the estimated amount is under 500,000 won so you owe nothing, you must submit the filing for the notice already issued to be cancelled. In contrast, double-entry bookkeeping obligors, who have no base amount, must file and pay on their own if they had business results in the first half.

Can you pay in installments if a lump sum is hard?

If the interim prepayment exceeds 10 million won, you can pay in installments. If the tax due is 20 million won or less, you can split off the amount above 10 million won, and if it is more than 20 million won, up to 50% of the tax. In the National Tax Service's example, with tax of 12.5 million won, you pay 2.5 million won in installments and pay 10 million won by November 30. The installment notice is sent in early January 2027, and the deadline is Monday, February 1, 2027.

Where and how do you pay?

On Hometax or Sontax, go to Tax Payment under the Payment, Notice, and Refund menu and choose the item whose tax category is notified amount, and you can pay by bank transfer, credit card, or simple payment. Service hours are 07:00 to 23:30. You can also transfer to the virtual account or National Tax account on the notice, or pay at a financial institution's counter.

What should you check last?

Match three things: the notice amount, your income type, and your first-half results. I wrote this on 2026-10-09 after opening and checking three public National Tax Service guidance pages. Tax law and deadlines can change, so after you receive your notice, look again at the latest guidance on Hometax and from the National Tax Service call center at 126.