I miscalculated and will not be back in Bkk until the day after my retirement extension expires (non immigrant o visa) Is it possible to re new it a few days late or is the date the absolute deadline, very worried about this as cannot change the travel dates.

I would say no.

You did have 30 days to do this.

EDITED AFTER I RE-READ THE O/P'S POST.

Unless I mis-read what you wrote, when you come back to Thailand you won't even have a valid extension of stay as it expires the day before you arrive here!

Is that correct?

If it is, about the best you can hope for is a 30 day visa exempt stamp when you arrive.

You'll most likely hafta start the entire process of a yearly extension of stay based on retirement all over.

Sorry about that. ..

FYI: Although it doesn’t help your current situation; please realize you can renew an extension of stay earlier than 30 days before it expires, with PROOF you're gonna be outta the country when your current extension expires.

I've done quite a few of these for acquaintances who were gonna be outta the country when their current extension expired. Thai Immigrations totally understands this sometimes happens.

One particular incident was nearly 3 MONTHS early, but he had proof, as in a travel itinerary that he was soon to be leaving Thailand and would not return before his extension expired. They granted it.

Still post back and let us know what happens, okay?

As said a re-entry permit would only allow return during the same period your extension of stay is valid. You will not have a valid entry method other than visa exempt so you might want to consider obtaining a new non immigrant O visa to return with and 60 days later doing a new retirement extension of stay.

EDITED AFTER I RE-READ THE O/P'S POST.

Unless I mis-read what you wrote, when you come back to Thailand you won't even have a valid extension of stay as it expires the day before you arrive here!

Is that correct?

If it is, about the best you can hope for is a 30 day visa exempt stamp when you arrive.

You'll most likely hafta start the entire process of a yearly extension of stay based on retirement all over.

Sorry about that. ..

FYI: Although it doesn’t help your current situation; please realize you can renew an extension of stay earlier than 30 days before it expires, with PROOF you're gonna be outta the country when your current extension expires.

I've done quite a few of these for acquaintances who were gonna be outta the country when their current extension expired. Thai Immigrations totally understands this sometimes happens.

One particular incident was nearly 3 MONTHS early, but he had proof, as in a travel itinerary that he was soon to be leaving Thailand and would not return before his extension expired. They granted it.

Still post back and let us know what happens, okay?

Very helpful thanks, can I take it a return air ticket would be proof enough to do the extension 37 days in advanxe instead of 30?

Should be ok . Immigration are usually quite helpful .