There will be an average £55 (4.8%) increase for customers taking both fuels, £36 (6.2%) for electricity-only customers and £19 (3.3%) for gas customers.
The changes come into effect on 16 August and are due to a “significant rise in the cost of wholesale energy” driven in part by the “Beast from the East”, the company said.
Chief executive Michael Lewis said: “We had hoped that by making the structural changes we made earlier this year, impacting bills by around £22 a year, we could avoid an increase in our unit price.
“However, as was seen in relation to the increases in the regulated prepayment cap in April, a number of costs have risen quite sharply and in particular we’ve experienced a hike in the price we have to pay for the energy our customers need, partly driven by the Beast from the East and extreme weather conditions experienced earlier this year.
“Through advanced purchases, we had been able to shield our customers from some, but not all, of this impact.”
E.ON said it had contacted around 1.8 million standard variable tariff customers to advise them that cheaper tariffs could be available.
The company will be writing to affected customers in the coming weeks to notify them of the change and will continue to offer choice and to advise customers of savings they could make on the cheaper tariffs available.
A government-enforced price cap set to be introduced on standard variable tariffs later this year.