Summary
If you make 31,079,381 원 a year living in South Korea, you will be taxed 4,724,331 원. That means that your net pay will be 26,355,050 원 per year, or 2,196,254 원 per month. Your average tax rate is 15.2% and your marginal tax rate is 21.8%. 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 21.82 원, hence, your net pay will only increase by 78.18 원.
Bonus Example
A 1,000 원 bonus will generate an extra 782 원 of net incomes. A 5,000 원 bonus will generate an extra 3,909 원 of net incomes.