The amount I calculate is Fix rate at 167,980.18 all year, but in fact his salary adjust on May, so the income Tax will be less than 28,870.05/month. However we can take this figure then we will get refund back from the Revenue Dept. approx. 20,000 baht.
For 2017 he have to pay Tax by himself so the figure was correct, he should be received some refund cause of SSO and PF approx. 2,000 baht.
Further assistance please do not hesitate to let me know, thank you very much for kind support.