When entering the Kingdom of Thailand, please be mindful of the last day on your stay permit and DO NOT stay longer than the permitted date.
Foreigners will be fined if they overstay in Thailand for less than 90 days. The fine depends on the number of days the foreigners have overstayed. The minimum charge is 500 Baht per day but does not exceed 20,000 baht in total. If the foreigners pay the fine before departure, they will not be banned for entering Thailand in the following visit.
Nevertheless, If you overstay for more than 90 days, you will be deported from Thailand and banned from visiting for a certain period of time. The length of the ban depends on how long you have overstayed your visa.