Summary
If you make 40,829,712 원 a year living in South Korea, you will be taxed 6,850,931 원. That means that your net pay will be 33,978,781 원 per year, or 2,831,565 원 per month. Your average tax rate is 16.8% and your marginal tax rate is 21.8%. 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 21.81 원, hence, your net pay will only increase by 78.19 원.
Bonus Example
A 1,000 원 bonus will generate an extra 782 원 of net incomes. A 5,000 원 bonus will generate an extra 3,910 원 of net incomes.