How many days should be left on my tourist visa to extend it by 30 days in Thailand?

If you're in Thailand on a 60-day tourist visa and want to extend it by 30 days, you can generally apply for the extension when you have 30 days left at most immigration offices. However, certain locations like Bangkok, Chiang Mai, Phuket, and Buri Ram allow you to apply up to 45 days in advance.