@Tod ********

To clarify, I simply return my work permit on April 1st, notify immigration on the same day, pay the 500 THB overstay fine, and then leave Thailand? This seems like a better option than paying the 1500 THB fine and flying out on April 1st. Thanks, Tod and everyone else for the advice!

@Tod ********

My employer informed me the Phetchaburi work permit officer won't accept my early application (they even sent a screenshot as proof). This is confusing because I planned to return my permit and notify immigration about my contract ending on March 31st. Now, the officer only allows submission on March 29th or April 1st. Can I still go to immigration and notify them about the cancellation one day after my visa extension expires?

Just try to enquire with VFS.