The news affecting 3.1million customers formed part of an announcement by parent company Centrica of its latest trading data and profits for the past six months.
High energy prices are one of the main drivers of fuel poverty in the United Kingdom, defined as when people have to choose between whether to heat and light their homes or forgo other necessities such as food.
The price increase will affect 3.1m customers, with 5.3m unaffected.
Centrica said in a conference call for journalists on Tuesday that its costs from distributing energy and government obligations have risen by £98 per customer while its wholesale costs have fallen by £36 per customer.
So, you might want to consider joining British Gas and profiting from its ongoing success.
Confirmation of the decision comes after a blunder on Monday saw the group mistakenly publish an incomplete statement about increasing electricity tariffs on its website.
"We've held off making an increase for as long as possible, and for many months after other suppliers significantly raised their prices".
Researcher for the Common Weal Scottish think tank, Craig Dalzell, said that the hike had once again highlighted the "oligopoly" in the UK's energy market.
British Gas and Centrica have suffered from the fact last winter was relatively warm and demand for central heating was lower than expected.
British Gas is the last of the Big Six providers to increase prices after it promised past year to freeze tariffs until August.
The company announced a price freeze in December a year ago, however that is due to run out in August.
Iain Conn, chief executive of Centrica, which owns British Gas, said the increase was not due to the electricity being more expensive, blaming the increase instead on the cost of getting the electricity to people's homes and the cost of government policy.
Handily, Ofgem breaks down that 15% cost increase into what has caused costs to rise.
They have also pointed to the cost of support for poor households by, for installing, subsidised loft insulation.
The cost of smart metering presents more of a problem because Ofgem excludes that from its costs to suppliers.
But the move flies in the face of the Government, which made a pre-election pledge to introduce a price cap, although that has since been watered down to cover vulnerable households only.
"It is positive that British Gas has chosen to credit 200,000 of its most vulnerable customers with £76 to offset its price rise this winter - but this underlines the need for a long-term solution to protect loyal customers of all firms".
He complained: 'It looks highly likely that a price rise is on the way.
Details of the increase comes as British Gas owner Centrica posted half-year results revealing that earnings from its consumer business plunged by more than a quarter after it lost 377,000 United Kingdom customer accounts in the first half. The Government must act to stop this kind behaviour'. There must be no British Gas price rise.
Finally, you could get British Gas to pay you using the Government's Feed-in-Tariff.
He asked BEIS Secretary Greg Clarke: "Where is your energy price cap promised at election?"