If you make NT$ 1,200,000 a year living in Taiwan, you will be taxed NT$ 132,977. That means that your net pay will be NT$ 1,067,023 per year, or NT$ 88,919 per month. Your average tax rate is 11.1% and your marginal tax rate is 13.9%. 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$ 13.85, hence, your net pay will only increase by NT$ 86.15.
A NT$ 1,000 bonus will generate an extra NT$ 862 of net incomes. A NT$ 5,000 bonus will generate an extra NT$ 4,308 of net incomes.