The best month to fly between Hanoi and Bangkok is November and the most expensive month to fly is September. (Average prices, based on 1155 datapoints.)
The cheapest airline flying from Hanoi to Bangkok is VietJet Air. They are 60% cheaper than Thai Airways. (Average prices, based on 1160 datapoints.)
The best time to fly is at around 9. (Average prices, based on 1199 datapoints.)