Hi - I'm arriving at BKK at 1540 on 31st Dec and am planning on flying to Kuala Lumpur with Air Asia which I believe departs from a different (low-cost) terminal.
There's an Air Asia flight that departs at 1800. Do you think we could make it?
Alternatively we will have to wait until 2020 and then arrive in KL at 2330..not much of a New Year's Eve!
thanks
Emma

There is no "low cost" terminal; it's all one airport. On the face of it, I'd say you would probably make it, but you might get into trouble if your incoming flight got significantly delayed. Why don't you stay in Bangkok and celebrate the new year, and then fly onward in the morning?

You should be fine on that 18:00 departure, Air Asia ex-BKK flights are usually quite delayed as the day progresses. You can probably count on at least a 30 minute delay.

Since you are on international connection, you should sort out the possibilities of checking bags through. Otherwise it could get messy. If no checked bags just follow the signs for international connections and look for the nearest transfer desk.

Since you are on international connection, you should sort out the possibilities of checking bags through.
The possibility is zero, as Air Asia doesn't do connecting flights, so you'll need to immigrate to pick up your bags and check-in again. You are, in theory, exempted from the 500 baht airport tax if you have a same-day transit, but accomplishing this in Don Muang was a challenge and I haven't heard from anyone trying it in Suvarnabhumi yet.