What are the consequences of not completing 90-day reports during a one-year stay in Thailand before leaving the country?

If you leave Thailand without having done your 90-day reports and without any overstay, nothing will happen at the airport, as immigration does not check for this at departure. However, on your next visit, an immigration officer may notice the lack of reports, resulting in a fine of around ฿2000 THB. Also, failure to complete these reports could restrict your ability to apply for in-country visas, extend your visa, or receive a residency certificate until the fine is resolved.