Ofgem has confirmed that the energy price cap will rise 4% from 1 October, taking the annual bill for a typical household to £1,723.
The increase adds about £60 a year to the current level of £1,663 and runs until 31 December.
The cap limits the maximum suppliers can charge per unit of gas and electricity, plus daily standing charges.
It applies to households on standard variable tariffs in England, Scotland and Wales, meaning anyone who has not moved to a fixed deal.
Customers on fixed contracts and households in Northern Ireland are unaffected.
The rise wipes out most of the government cut to VAT from electricity bills. That measure reduced the tax from 5% to zero on electricity unit rates and standing charges for six months from 1 October, though gas will continue to carry 5%.
Analysts said continued uncertainty linked to the conflict in the Middle East has pushed wholesale energy prices higher, more than offsetting the effect of the VAT cut.
Heatwaves across Europe added further pressure by lifting gas demand for power generation to run cooling systems.
Cornwall Insight, the consultancy whose forecasts are closely tracked in the sector, had predicted a slightly higher figure of £1,729 in its final estimate.
On a unit-for-unit basis, the new cap is the highest since July 2023. The figure is measured against Ofgem's revised definition of a typical household, introduced on 1 July to reflect falling average energy use.
On the previous basis, the current cap equates to £1,862 a year. The increase lands as households start using their heating more regularly, adding further to bills.
Jess Ralston, head of energy at the Energy and Climate Intelligence Unit, said energy debt was already at record levels before winter had begun, and that Britain remains highly exposed to volatile gas prices.
The government has pointed to the VAT cut, the £150 warm home discount for around six million households, and its warm homes plan.
