Do I need to prove overseas funds and maintain a minimum balance for a Non-O extension in Thailand?

It might be worth keeping a bit more than 400k in your account in case bank charges are applied during the 2 months prior to application for the extension. I have noticed that some people have reported that they had exactly 400k in their account then bank charges were applied during the 2 month seasoning period which messed up their plans as it took the balance below 400k. Just something to watch out for.

Funds don’t need come from overseas. Just need that 400k 2 months before applying for the extension. Doing again in few months

Q1. Do I need to prove that the funds came from on overseas source?

-> Funds for a 1-year extension don't require international transfer.

Q2. Is there a minimum balance required in my Thai bank account throughout the year?

-> No minimum balance throughout the year other than seasoning. Your balance can be even zero after you get an extension.

Q. As in, what if I temporarily go below 400k baht at some point during the year, so long as it isn’t within the 3 months before renewal; is this a problem?

-> It wouldn't be an issue. However, better to ask your office along with the application for an extension whether they want you to bring the updated passbook when you go back to the office after the under-consideration period.

No and no, once your extension is inked in the funds are accessible. must be topped up 2 months prior to extension renewal application date. Verify requirements with your local immigration office.

2. You can use all the balance if you like, as long as it is 400k for the 2 months preceding your next extension. Wise to keep it at 400k during the 'under consideration' period too.

1. No