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 Hanoi is October and the most expensive month to fly is August. (Average prices, based on 257 datapoints.)
The best day to arrive at Bangkok is Thursday and it would be best to avoid Wednesday, as prices are on average 94.28% higher than on Thursday. (Average prices, based on 282 datapoints.)
The cheapest airline flying from Bangkok to Hanoi is Thai AirAsia. They are 49% cheaper than Thai Airways. (Average prices, based on 267 datapoints.)
The best time to fly is at around 6. (Average prices, based on 500 datapoints.)