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 Medan is September and the most expensive month to fly is June. (Average prices, based on 257 datapoints.)
The best day to arrive at Bangkok is Wednesday and it would be best to avoid Monday, as prices are on average 23.27% higher than on Wednesday. (Average prices, based on 257 datapoints.)