Can I extend my 30-day visa exemption in Thailand for another 30 days, and when does the extension start?

If you enter Thailand on a 30-day visa exemption, you can apply for a one-time 30-day extension at most immigration offices when you have 30 days or less left on your existing stamp. In Bangkok, you do not have to wait until the last week to apply for the extension; you can go to the office any time during that period. The extension period will start from the date you apply, effectively adding the new 30 days to the end of your current visa validity.