Summary
If you make 6,659,916 บาท a year living in Thailand, you will be taxed 1,854,356 บาท. That means that your net pay will be 4,805,560 บาท per year, or 400,463 บาท per month. Your average tax rate is 27.8% and your marginal tax rate is 34.3%. This marginal tax rate means that your immediate additional income will be taxed at this rate. For instance, an increase of 100 บาท in your salary will be taxed 34.28 บาท, hence, your net pay will only increase by 65.72 บาท.
Bonus Example
A 1,000 บาท bonus will generate an extra 657 บาท of net incomes. A 5,000 บาท bonus will generate an extra 3,286 บาท of net incomes.