All, need your expertise on the following:

I am on a Retirement Visa and have extension of stay until August 21st. I travel a lot and also have a multiple re-entry permit.

If I travel and re-enter Thailand on say August 10th, will immigration still stamp me until August 21st or give me a 30 day stamp and my extension is then invalid? Do I need to re-enter Thailand at least 31 days ahead?

Also what is the time period one can apply the next extension of stay? 7 days before or how long before expiry?

thanks

you will be stamped until the 21st if you use the re-entry permit.

You can be given a 30 day visa on arrival with proof of onward flight, but this and any other visa will cancel your original Retirement visa, so that a new application would have to be made, maybe in another country first.

Apply for an extension anytime, I usually apply 14 days in advance of the validity date of the current extension.

You can apply for up to 30 days early, the extension will still start when the current permisison to stay ends, so you don't lose any days.

In case of necesity, like traveling, they might even do it earlier than 30 days.