When can I apply for a 30-day extension on my tourist visa in Thailand?

The user is currently on a 60-day tourist visa and seeks to apply for a 30-day extension before their flight back to London on January 18, 2026. The inquiry focuses on when they can apply for the extension and how it affects their leaving date. Responses indicate that at most immigration offices, one can apply for an extension with 30 days or less remaining on their current visa, and the extension time is added to the expiration date.