Summary
If you make 66,040,000 원 a year living in South Korea, you will be taxed 12,693,117 원. That means that your net pay will be 53,346,883 원 per year, or 4,445,574 원 per month. Your average tax rate is 19.2% and your marginal tax rate is 23.4%. 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 23.38 원, hence, your net pay will only increase by 76.62 원.
Bonus Example
A 1,000 원 bonus will generate an extra 766 원 of net incomes. A 5,000 원 bonus will generate an extra 3,831 원 of net incomes.