"Withholding tax" in Thailand is a term applied to many taxes, but the most common one that business owners come up against is the 3% deducted by customers from your sales invoice. The 3% is deducted from the "service" before VAT (currently 7%), and is paid over to the Revenue Department by the customer at the end of each calendar month. The customer is required to give you a certificate (duly signed) which must be kept carefully, as it is your evidence to the Revenue Department that you can claim against your company"s annual tax bill.

The subject is far more complex than this simple explanation, and can be looked up on the Revenue Departments website, in English