How many days before my return ticket or visa expiry should I apply for a one-month extension at immigration?

The timing for applying for a one-month visa extension at immigration in Thailand depends on the specific immigration office. Larger offices, such as those in Bangkok, Phuket, and Chiang Mai, typically allow applications when there are 45 days or fewer remaining on your current stay. Most other offices permit applications with 30 days or fewer left. However, some offices, like those in Jomtien/Pattaya, Koh Samui, and Koh Phangan, only accept applications during the final week of your visa.