The month of October is, on average, the cheapest month to fly to Bilbao from Ireland, with most prices found around 125€. If you don’t want to visit Bilbao in October, then you should wait until January to fly from Ireland, when ticket prices are also cheap, with an average price of 126€.
The best time to book a flight to Bilbao from Ireland is 46 days out, which is when prices tend to be around 162€. Don’t hesitate to check prices now though, because momondo users recently found tickets for as low as 155€.
The cheapest day to depart from Ireland to Bilbao is on a Tuesday when prices can be found for as low as 152€. Flights from Ireland to Bilbao on a Sunday will generally be more expensive and average around 201€. Keep in mind that these prices on both days could fluctuate depending on the season and the demand.