Please be aware that Seoul has multiple airports and that these results are for all airports serving the city.
The best month to fly between Seoul and Jeju City is April and the most expensive month to fly is March. (Average prices, based on 534 datapoints.)
The best day to arrive at Seoul is Tuesday and it would be best to avoid Thursday, as prices are on average 620.92% higher than on Tuesday. (Average prices, based on 530 datapoints.)