Summary
If you make 21,045,440 원 a year living in South Korea, you will be taxed 2,696,600 원. That means that your net pay will be 18,348,840 원 per year, or 1,529,070 원 per month. Your average tax rate is 12.8% and your marginal tax rate is 15.8%. 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 15.75 원, hence, your net pay will only increase by 84.25 원.
Bonus Example
A 1,000 원 bonus will generate an extra 843 원 of net incomes. A 5,000 원 bonus will generate an extra 4,213 원 of net incomes.