If you make NT$ 5,000,000 a year living in Taiwan, you will be taxed NT$ 1,218,724. That means that your net pay will be NT$ 3,781,276 per year, or NT$ 315,106 per month. Your average tax rate is 24.4% and your marginal tax rate is 39.5%. This marginal tax rate means that your immediate additional income will be taxed at this rate. For instance, an increase of NT$ 100 in your salary will be taxed NT$ 39.50, hence, your net pay will only increase by NT$ 60.50.
A NT$ 1,000 bonus will generate an extra NT$ 605 of net incomes. A NT$ 5,000 bonus will generate an extra NT$ 3,025 of net incomes.