Please be aware that Seoul and Beijing has multiple airports and that these results are for all airports serving the city.
The best month to fly between Seoul and Beijing is September and the most expensive month to fly is January. (Average prices, based on 208 datapoints.)
The best day to arrive at Seoul is Monday and it would be best to avoid Saturday, as prices are on average 62.96% higher than on Monday. (Average prices, based on 221 datapoints.)
The cheapest airline flying from Seoul to Beijing is Air China. They are 15% cheaper than Korean Air. (Average prices, based on 219 datapoints.)
The best time to fly is at around 13. (Average prices, based on 233 datapoints.)