Founding as a Developer — Validate Before You Build
The Skeleton of Incorporation and Taxes — What Is Due, When, and Where
In one line
The procedure for setting up a corporation can be handled online in one go, and once it is set up, a fixed calendar starts running — business registration (within 20 days of the business start date), value-added tax (a six-month taxable period, final return within 25 days after it ends), withholding tax on salaries (the 10th of the following month), and corporate tax (within 3 months from the last day of the month in which the fiscal year ends). What a developer should remember is not the numbers but the fact that this calendar exists and where to look at the original text.
This article is not legal or tax advice. It is an overview checked on 2026-09-24 against the official sources below, and laws and notices change. Before making an actual decision, check the original text and a professional (tax accountant, lawyer, judicial scrivener).
Why this was needed
The accident developer founders suffer most in their first year is not the product but the deadline. They register the business late and pay a penalty tax, they cannot claim input tax credit on equipment bought before registration, and they pay the first employee's salary and forget to file the withholding tax. Each is a small sum of money, but it makes you go back and forth to the tax office and paperwork just when you should be saving time the most.
You do not need to memorize every deadline. Most companies entrust it to a tax agent. But if you do not know what comes around and when, you can neither choose what to entrust nor check the result of what you entrusted.
How it works
Incorporation. The Online Corporation Establishment System run by the Ministry of SMEs and Startups is a window built so that the procedures for setting up a corporation, from name search to enrolling in the four major social insurances, can be handled online. The introduction on Policy Briefing states that it connected online what used to require visiting 7 agencies and preparing some 30 kinds of documents.
Corporation establishment report and business registration. The Ministry of Government Legislation's Easy-to-Find Everyday Law Information guides that a corporation must apply for the corporation establishment report and business registration to the head of the tax office with jurisdiction over its place of tax payment within 20 days of the business start date for each business place, and cites Articles 109 and 111 of the Corporate Tax Act as the basis. The same guide states that a penalty tax is added if the deadline is exceeded and that input tax before registration cannot be credited. You can apply for registration even before you start the business, so it is better to register before you buy equipment or servers.
Value-added tax. Article 30 of the Value-Added Tax Act sets the tax rate at 10 percent. According to the National Tax Service's filing and payment deadline guide, the taxable periods for general taxpayers are Period 1 (January 1–June 30) and Period 2 (July 1–December 31), and corporate businesses file a preliminary return in the middle of each period (April and October 1–25) and a final return after it ends (July and January of the next year, 1–25). A small corporation whose supply value in the immediately preceding taxable period was under 150 million won is notified of half of the tax paid for the preceding period and pays that, instead of filing a preliminary return.
Withholding tax. When you pay employees salaries, the company deducts tax and pays it on their behalf. The National Tax Service's withholding tax guide states that it is filed and paid by the 10th of the month following the month in which the tax is collected, and for those eligible for semiannual payment, by the 10th of the month after the last month of the half year.
Corporate tax. Article 60 of the Corporate Tax Act requires filing within 3 months from the last day of the month in which each fiscal year ends. For a corporation with a December fiscal year-end, that is March 31 of the next year.
| What | When | Where to check |
|---|---|---|
| Corporation establishment report and business registration | Within 20 days of the business start date | Everyday Law Information, National Tax Service |
| Value-added tax (corporation) | April, July, October, and January 1–25 | National Tax Service filing and payment deadlines |
| Withholding tax | The 10th of the next month (for semiannual payers, January and July 10) | National Tax Service withholding tax |
| Corporate tax | Within 3 months from the last day of the fiscal year-end month | Article 60 of the Corporate Tax Act |
What it looks like in the field
- You bought development equipment before registering the corporation and cannot claim the input tax credit.
- You started paying a salary to just one co-founder, did not know about the withholding tax return, and penalty tax attaches from the first month.
- You entrusted it to a tax agent, but since you do not know the calendar, you do not know when documents are needed and scramble to find them every time.
The numbers in this table were checked on 2026-09-24. Tax law changes every year, so do not trust the table; trust the links in the table.
What you will do in the next reading
You look at two things attached on top of the skeleton of taxes — how to read government startup support programs, and the order for checking systems whose requirements are written down, such as investment contracts (conditional equity acquisition agreements) and tax reductions.