Can I get a 30-day extension in Chiang Rai if I'm registered in Chiang Mai?

Chiang Mai lets you apply for an extension when you have 45 days or less left on your current stamp and I think Chiang Rai allows you to apply when you have 30 days or less left. So you can go get your extension when ever you want to.

There is no upside to waiting until the stamp you have almost expires because they add the extension to your current expiration date.

Good Luck (y)

you need to use an address in the area that is served by that immigration office <- meaning you can't put a chiang mai address applying at chiang rai for the extension.

Always go early

I guess you did a border run to get a new Visa Exempt Entry and you can apply for the Extension of Stay in Chang Rai. This Visa Exempt Entry is for short time tourists and Immigration does not expect people using this for living in Chang Mai.

The best plan is ask the immigration in Chiang Mai if you can extend your extension to Chiang Rai. I believed they’re friendly.

Chiang Mai report

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You should get it where you are registered to live. But lets await and see what others say.

What is a "30 day"? You mean you extension of stay?