When is the latest date to apply for a yearly extension with a Spouse/Family Visa in Thailand?

When you apply for a yearly extension based on marriage you get a 30 day under consideration stamp in your passport. that's the date you go back to get the year extension inked in. OR if it's going to be earlier they call you and tell you when you come back.

This is what the 30 day under consideration stamp looks like when you apply for the year extension based on marriage

I would suggest you stop in to the immigration office BEFORE you're going to apply for the extension and get the hand out (if they have one) listing the required documentation, photos, copies, etc so that when you do go for the extension you have what you need to pull it off.

Also remember, extensions based on marriage go 'under consideration' for 30 days and then you go back and get the year extension inked into your passport. During that time they usually make an in home visit to make sure the marriage is on the up and up..

Good Luck

So you would be applying for a yearly extension of stay based on marriage to a thai by meeting the financial requirements of 400K baht in a thai bank account in your name only for 2 months prior to you applying for the extension right?

You can apply for an extension of stay at MOST immigration offices when you have 30 days or less left on your current stamp.

Bangkok, Buriram, Chiang Mai & Phuket allow you to do it when you have 45 days or less left on your current stamp..

The LATEST date would be the day your current stamp expires <- BUT I would say don't hold it off that long because if you're missing a document you got no time left to get it and get back to apply for the extension..