With tourist visa, can you leave during the 60/90 days and re-enter within that time? Say I enter on day 1, and on day 14 I leave to Vietnam for 2 weeks. Can I reenter and use the tourist visa until it expires?

Thanks in advance!

Edited July 18, 201213 yr by patjk

Not unless it's a double or triple entry visa.

Leaving means the visa has been used and cannot be re-used. You could see about applying for some kind of re-entry permit, although others much more expert than I can advise on the possibilities of that.

Can I reenter and use the tourist visa until it expires?

With a re-entry permit, you can. Using your example:

01 AUG: arrival in Thailand. Permission to stay until 29 SEP.

14 AUG or earlier: get 30-day extension; this extends your permission to stay until 29 OCT. Then get single-entry re-entry permit; this will be valid for a return entry until 29 OCT.

14 AUG: travel to Vietnam.

28 AUG: return to Thailand; you receive permission to stay until 29 OCT.

29 OCT or earlier: leave Thailand

A re-entry permit requires application at Immigration prior to departure and will cost 1,000 baht (a bit more at airport).