If you make NT$ 6,000,000 a year living in Taiwan, you will be taxed NT$ 1,613,747. That means that your net pay will be NT$ 4,386,253 per year, or NT$ 365,521 per month. Your average tax rate is 26.9% 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.