In general, when looking for the cheapest flight to Seoul, try to choose a flight departing in March for the best deal.
From most locations, booking your flights to Seoul around 60 days prior to your departure date finds the best deals.
On average, the cheapest flights to Seoul are found when departing on a Tuesday. Try to avoid departing on a Saturday, as this is usually the most expensive day.
Generally, when visiting Seoul, evening flights represent the best value. morning flights are likely to have higher prices.