When does the 30-day extension start for my tourist visa in Thailand?

but you potentially lose a day if you come in on a late flight. 5 minutes to midnight and thats your first day wasted

You had a tourist visa that was valid for 90 days <- meaning you have 90 days to enter the country. When you entered you were stamped in for 60 days <- the length of time ALL tourist visas give people when they enter the country.

You can go to the immigration office when you have 30 days or less left on your current stamp and apply for a 30 day extension for 1900baht.

They will add the 30 days onto the existing expiration date of the stamp you have (Dec 14). You don't lose any days by going early.

Please read the stamm of THW Extension , normaly IT say u have to leave on The Date mentioned....." Up to"