Summary
If you make 12,939,701 원 a year living in South Korea, you will be taxed 1,540,281 원. That means that your net pay will be 11,399,420 원 per year, or 949,952 원 per month. Your average tax rate is 11.9% and your marginal tax rate is 12.7%. This marginal tax rate means that your immediate additional income will be taxed at this rate. For instance, an increase of 100 원 in your salary will be taxed 12.67 원, hence, your net pay will only increase by 87.33 원.
Bonus Example
A 1,000 원 bonus will generate an extra 873 원 of net incomes. A 5,000 원 bonus will generate an extra 4,367 원 of net incomes.