Summary
If you make 128,999,988 원 a year living in South Korea, you will be taxed 32,940,330 원. That means that your net pay will be 96,059,658 원 per year, or 8,004,971 원 per month. Your average tax rate is 25.5% and your marginal tax rate is 40.7%. 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 40.69 원, hence, your net pay will only increase by 59.31 원.
Bonus Example
A 1,000 원 bonus will generate an extra 593 원 of net incomes. A 5,000 원 bonus will generate an extra 2,966 원 of net incomes.