Summary
If you make 8,699,990 원 a year living in South Korea, you will be taxed 1,003,168 원. That means that your net pay will be 7,696,822 원 per year, or 641,402 원 per month. Your average tax rate is 11.5% 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 12.66 원, hence, your net pay will only increase by 87.34 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.