My Non-O retirement visa expires in March. I plan to leave Thailand temporarily in early April and would prefer not to renew it until I return. How many days after my Non-O expires do I have to leave the country?

Zero days after.

The non O stamp expiry date is the last day you can exit to avoid overstay. 

How many days past your stamp expiry do you plan to exit Thailand. 

You're going to need to either border bounce for a 60 day visa exempt stamp before your extension runs out, or you're going to need to apply for the 1-year extension.  Those are the only options without going on overstay, which you should never do.

1 hour ago, BrandonJT said:

You're going to need to either border bounce for a 60 day visa exempt stamp before your extension runs out, or you're going to need to apply for the 1-year extension.  Those are the only options without going on overstay, which you should never do.

He can apply for a 60 day extension if he has a Thai Wife or apply for an extension get refused and be given 7 days to leave the country.

 

18 hours ago, OzMan said:

My Non-O retirement visa expires in March

Read your other thread.

You refer to "retirement visa" 

What do you actually have. 

A Non O-A (doubt it) 

A Non O retirement that would have only provided a 90 day permission of stay stamp (doubt it) 

A 12 month extension (no) 

 

Your thread April last year stated......

"I have a non-O retirement visa and plan to travel to Spain this Saturday. I believe I can leave Thailand once without paying the 1,200 baht for a re-entry permit. Can I just walk through immigration on the way out, and then just turn up at immigration on the way back, and my non-O will be renewed?" 

 

What? 

"visa has expired". Really easy to understand. 

9 hours ago, Lite Beer said:

He can apply for a 60 day extension if he has a Thai Wife or apply for an extension get refused and be given 7 days to leave the country.

 

That would be my understanding, but don't think there is a wife to come into it.

Of course it would cost the 1900 baht to make a failed application and get the 7 days grace period.