Please be aware that Bangkok has multiple airports and that these results are for all airports serving the city.
The best month to fly between Bangkok and Hat Yai is May and the most expensive month to fly is March. (Average prices, based on 535 datapoints.)
The best day to arrive at Bangkok is Wednesday and it would be best to avoid Friday, as prices are on average 36.73% higher than on Wednesday. (Average prices, based on 7161 datapoints.)