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 Siem Reap is June and the most expensive month to fly is December. (Average prices, based on 2276 datapoints.)
The best day to arrive at Bangkok is Thursday and it would be best to avoid Saturday, as prices are on average 10.98% higher than on Thursday. (Average prices, based on 2057 datapoints.)