Thailand Visa On Arrival is valid for a maximum of 15 days, and it cannot be extended. Overstaying on your Thailand visa on arrival will result in a fine. Depending on the duration of the overstay, the fine may range from 500 Thai Baht to 20,000 Thai Baht. If you intend to stay longer than 15 days in Thailand, it is recommended that you apply for a regular Thailand tourist visa.