0-A 2 or 3 months

11 minutes ago, KeeTua said:

I plan to switch from the monthly 65k income method to 800k in bank. I understand the 800k needs to be there for 2 months prior and 3 months after.

As it won't be my first extension do I need to show a minimum balance of 400k for the 12 months prior to application for extension or will the 800k two months prior suffice?

According to the rules, you must have maintained a minimum balance of 400,000 baht for the entire year. If you had the required 65,000 baht per month transfers for the period when you had a balance beloww 400,000 baht, maybe you can talk them into overlooking the shortfall.