What is the process and consequences of overstaying a visa in Thailand?

When a person overstays their visa in Thailand, there are significant consequences based on the length of the overstay. If the overstay is 90 days or less, a fine of 500 baht per day applies, capped at 20,000 baht, and an overstay stamp is placed in their passport, allowing them to leave without further issues. If the overstay exceeds 90 days, the penalty escalates to a flat fee of 20,000 baht and a ban from re-entering Thailand, which varies depending on how long the overstay lasted. If caught by authorities or at a random checkpoint, the overstayer may face detention, deportation, and possible long-term bans on re-entry. Seeking the help of an immigration agent may facilitate the exit process but can come with high costs depending on the length of the overstay.