When should I apply for a 30-day visa extension before my current visa expires?

To apply for a 30-day extension to your 60-day visa, you should generally do it when you have 30 days or less remaining on your current visa. Most immigration offices allow you to apply within this window, while larger cities like Bangkok, Chiang Mai, and Phuket may permit applications when you have as much as 45 days left. However, some locations like Jomtien, Koh Samui, and Koh Phangnan restrict applications to within the last week of your visa term. In your case, consider applying for the extension around March 26th to stay until April 14th.