In general, when booking your flight to Bilbao, June is the cheapest month on average.
In general, most flyers find the cheapest time to book a flight to Bilbao is about 60 days prior.
On average, the cheapest flights to Bilbao are found when departing on a Tuesday. Try to avoid departing on a Friday, as this is usually the most expensive day.
Generally, when visiting Bilbao, midday flights represent the best value. evening flights are likely to have higher prices.