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 Udon Thani is May and the most expensive month to fly is April. (Average prices, based on 1332 datapoints.)
The best day to arrive at Bangkok is Wednesday and it would be best to avoid Friday, as prices are on average 28.01% higher than on Wednesday. (Average prices, based on 1690 datapoints.)