If you make $ 4,000,000 a year living in Taiwan, you will be taxed $ 854,515. That means that your net pay will be $ 3,145,485 per year, or $ 262,124 per month. Your average tax rate is 21.4% and your marginal tax rate is 30.0%. This marginal tax rate means that your immediate additional income will be taxed at this rate. For instance, an increase of $ 100 in your salary will be taxed $ 30, hence, your net pay will only increase by $ 70.
A $ 1,000 bonus will generate an extra $ 700 of net incomes. A $ 5,000 bonus will generate an extra $ 3,500 of net incomes.