Suppose you're in Thailand and realize it's such a fantastic place, you'd like to stay for longer than you'd originally planned. If you have that luxury, you'll still need to make sure you can remain in the country legally for the extra time and that could mean extending your visa. The type of visa or entry permit you have will determine how much longer you can extend your stay in the country.
If you didn't enter Thailand with a tourist visa already in hand, chances are you got a 30-day entry permit when you arrived at the airport or border crossing.
If you entered Thailand with a tourist visa that you'd applied for before your trip, you probably have a 60-day tourist visa.
Thailand Visa Extension
If you have a 60-day tourist visa, you can extend it for up to 30 days. If you have a 30-day entry permit, you can extend it for up to 7 days.
Extending your visa or entry permit is not that convenient, in fact, it's sort of a pain unless you happen to be very close to an Immigration Bureau office. Check out the Immigration Bureau Locations to figure out where you have to go. You cannot extend at a border crossing.
Whether you have a 60-day tourist visa and you're applying to extend it for 30 days, or you have a 30-day entry permit and you're applying to extend it for 7 days, you'll pay the same fee, currently 1,900 baht. To apply, you will need to fill out a form and provide a copy of your passport (don't worry, there are places to make copies in most immigration offices if you forget) and a passport photo. It usually takes an hour or so from start to finish.