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 Hong Kong is August and the most expensive month to fly is February. (Average prices, based on 359 datapoints.)
The best day to arrive at Bangkok is Monday and it would be best to avoid Thursday, as prices are on average 220% higher than on Monday. (Average prices, based on 615 datapoints.)
The cheapest airline flying from Bangkok to Hong Kong is Hong Kong Express. They are 62% cheaper than Cathay Pacific. (Average prices, based on 378 datapoints.)
The best time to fly is at around 2. (Average prices, based on 844 datapoints.)