The tax bill you cite is incorrect. The first 150,000 is zero rated. That leaves 530,000. The next 150,000 is taxed at 5% (7,500). That leaves 380,000. The next 200.000 is taxed at 10% (20,000). That leaves 180,000 taxed at 15% (27,000). A total of 54,500 baht.