Will I be permitted to stay exactly 90 days in Thailand if I have a non immigration visa? I plan to stay in Thailand for 111 days and I think a week or two before the visa expires, I'll apply for an extension at the Bangkok Immigration office for the remaining days. I am a U.S. citizen and I go to Thailand once a year. Each time I stay around 3 months. I avoid applying for a visa by leaving the country every 30 day. I have no plans to go anywhere outside the country for this coming trip.

What kind of visa are you getting? If a tourist visa you should a apply for a 2 entry this time.

You will not get more than a 7 day extension here unless it is a tourist visa entry that you have not extended yet.

You would have to make a border run that gives you 15 days and extend for 7 days or fly out and back to get 30 days in order to get the extra 21 days you need if you don't get a 2 entry visa.

Non Imm O Visa 90 days. Cannot extend it. As UJ said you will have to do a border run or get a different Visa before you come.

I think I had a case of not enough coffee yet when I anwered your post. I missed the "if I get a get non immigrant visa?" part.

On what basis do you plan on getting the visa?

If it is a non-o visa for being over 50 there is no chance of getting more than a 7 day extension. If for marriage to a Thai or having a Thai child you could get a 60 day extension.

Otherwise the best choice is a 2 entry tourist visa. The cost will be the same as a single entry non immigrant visa.

It would mean a border run to get 120 days from the visa.

I suggest you use an honorary consulate to get the visa. For a list of them use the pulldown menu at the top to this webpage. http://www.thaiembdc.org/AboutEmb/EmbDirect.aspx