Summary
If you make 342,160,000 원 a year living in South Korea, you will be taxed 125,253,913 원. That means that your net pay will be 216,906,087 원 per year, or 18,075,507 원 per month. Your average tax rate is 36.6% and your marginal tax rate is 44.7%. 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 44.66 원, hence, your net pay will only increase by 55.34 원.
Bonus Example
A 1,000 원 bonus will generate an extra 553 원 of net incomes. A 5,000 원 bonus will generate an extra 2,767 원 of net incomes.