I just got aware of my bank withdraw Interest every month from my interests earned. Never heard about it, so Im wondering if every bank do that ?

Now I know, and better get my tax number now ?

When it comes to paying tax on interest there are two choices (for foreigners):

a) deduction of 15% at the source (bank)... usually set up automatically when you open bank account

b) pay at the time of filing your taxes. To go this route foreigners must get a Thai tax ID, take it to the bank and convince them to not withhold taxes from interest payments. I have heard that if over the course of a year you receive over 20K in interest the banks will resume withholding.

I believe the first 20K ฿ of income from interest is not subject to Thai income tax.

Several posters have failed to get the banks to stop the withholding of tax. Maybe I am luckier than I realize... I didn't have any trouble at SCB, BBL, KBank or Krungsri. I'm not sure if it is all banks, but Bangkok bank said they MUST withhold tax from interest on fixed deposit accounts.

Dependent on one's financial situation, my understanding is one advantage (if one receives a LOT of Thai interest) of having the 15% withholding tax on one's Thailand bank/bond interest, is if if the withholding tax is withdrawn automatically by the bank, then (per Thailand tax law) , that satisfies one's legal tax filing obligations for that interest, and such need not then be included in the assessment whether a Thailand tax return need to be filed.

I presume if one's bank/bond interest in Thailand is relatively small, and if one has no other remitted income to affect one's income status in Thailand, then one may wish to consider trying getting back that withholding tax. I don't fall into that category (of qualifying for a return of withholding tax) , so I have never pursued that.