Summary
If you make 80,999,364 원 a year living in South Korea, you will be taxed 16,957,152 원. That means that your net pay will be 64,042,212 원 per year, or 5,336,851 원 per month. Your average tax rate is 20.9% and your marginal tax rate is 28.6%. 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 28.63 원, hence, your net pay will only increase by 71.37 원.
Bonus Example
A 1,000 원 bonus will generate an extra 714 원 of net incomes. A 5,000 원 bonus will generate an extra 3,569 원 of net incomes.