The cheapest day to depart on your flight to Kolkata is on a Wednesday when prices can be found for as low as 638€. This is often the case because there is less demand to fly during this day of the week. Flights from Ireland to Kolkata on a Thursday will generally be more expensive and average around 964€. Keep in mind that these prices on both days could fluctuate depending on the season and the demand.
The cheapest time of day to fly to Kolkata is in the morning when flights can be purchased for as low as 682€. Try not to purchase tickets in the evening because they tend to be around 947€. Of course, these prices can vary depending on the time of year and what airport you fly to.