What is the latest date to apply for a one-year visa extension in Thailand before the visa expires?

The latest date to apply for a one-year visa extension in Thailand is typically the day before your visa expires, which means if your visa ends on the 30th, you should aim to apply by the 29th. Most immigration offices allow applications from 30 days prior to the expiration date up until the last day. However, it's recommended to have your paperwork in order and apply a few days earlier to avoid potential issues.