When do the 7 days to leave Thailand start if my extension of stay is denied before my visa expires?

If you apply for a 30-day extension of stay before your visa expires and it is denied, you will have 7 days to leave Thailand starting from the day after your visa expires, not the day you applied for the extension. For example, if your current visa expires on the 15th and your extension is denied, the 7-day countdown begins on the 16th and runs until the 22nd.