If you make NT$ 3,000,000 a year living in Taiwan, you will be taxed NT$ 563,611. That means that your net pay will be NT$ 2,436,389 per year, or NT$ 203,032 per month. Your average tax rate is 18.8% 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 NT$ 100 in your salary will be taxed NT$ 30, hence, your net pay will only increase by NT$ 70.
A NT$ 1,000 bonus will generate an extra NT$ 700 of net incomes. A NT$ 5,000 bonus will generate an extra NT$ 3,500 of net incomes.