Electric Picnic organisers have confirmed the date change from next year is to accommodate specific artists they are hoping will play.
The three-day festival is underway in Stradbally in County Laois, but from next year, it will move to mid-August.
Organiser Melvin Benn would not confirm the artists in question but said some of next year’s acts could not make it in September.
"There were some artists we wanted to talk to and were interested in playing but could only make a couple of dates," he said.
"I just wanted to explore it, really, to see whether it would work, and various circumstantial reasons.
"Essentially some of the artists that we wanted to play next year could only play two weeks earlier.
"We just took a decision that we thought was the right thing, really."
Billie Eilish is on the main stage tonight; however, she is the only female headliner this year, which has led to some criticism.
Mr Benn reiterated that they want more female headliners at the festival but claimed there are not enough available.
"Essentially, there are less female acts that have reached that headline status," he said.
"It's inappropriate to put acts on in a slot that they can't hold, and that wouldn't do anybody's career [any] good.
"We try very hard every year to get more and more females on the bill and as high up on the bill as possible.
"Touring schedules, publishing deals, record deals, etc - lots of things limit that opportunity," he added.
