When should I go to immigration to renew my marriage visa before it expires?

as Tod advised go to immigration in your area to get info of what they request..only thing I can add is double check what they want for photos..I was refused my extension last week because I didn't have a photo of us together outside the house showing the roof,although we had a photo of us outside showing the door and front deck..also had photos us us on the bed,in front of the TV,in the kitchen and also in front of the house number..and it might take several trips to Immigration to satisfy their needs lol.

Filled out TM7 w/passport photo

Copies of

-data page of your passport,

-your original visa,

-every extension,

-most recent entry stamp, -

TM6 departure card,

-TM30 receipt (I always copy the TM30 with the last 90 day report slip too)

-Original Kor Ror 3 marriage certificate & copy

-new Kor Ror 2 (if yours is older than a year) and copy

-update the bank book on the date you apply.

-copy of the data page of the bank book and every relevant page

-Bank letter (no more than 7 days old)

-hand drawn map to your house

-photo of you and your wife standing in front of the address numbers of your place

-photo of you and your wife sitting at the table and on the couch (you need two photos like that)

-thai i/d of your wife

-thai house book of your wife

-bring your lease but don't give it to them unless they ask

You sign every copy in BLUE pen that has your name on it, your wife signs every one that has hers and you both sign the marriage certificate copies

That's strictly from memory but it's pretty close to what they need.

In Bangkok you can apply for a new extension when you have 45 days or less left on your current stamp

So in your case IF you meet the proof of funds (seasoning etc) you could have applied any time after Oct 12.

Go when ever you get the documentation together. There is no reason to wait for it to run out because the add the new extension to your current stamps expiration date