Energy bills are set to rise for gas and electricity customers this week as some cheap fixed energy deals finally lapse.

Ofgem sets its price cap for energy bills every three months. The price cap is supposed to be a safety net to prevent companies from massively overcharging households who never bother to change tariffs or providers. Based on the cost of generating energy, the rates are set by the energy regulator and represent the maximum per unit of gas or electricity that a household will pay in a given period, plus the daily standing charges.

The only way to get your energy for less than the price cap is to grab a fix. Fixed deals usually undercut the price cap as different companies like British Gas, E.On and EDF all battle to attract customers from one another.

But this week, several of the cheapest fixed deals from the past year are running out, which means customers will see their monthly bills increase significantly unless they take action now.

For example, Outfox The Market’s March 2024 tariff, which gave customers a typical annual bill of £1,535 on average, runs out on Saturday, April 12. It means those on the tariff will be moved onto the standard variable price cap unless the grab another fix.

The standard variable price cap is currently set at £1,849 for a typical average bill, an increase of a whopping £314 against the old fixed deal.

In a similar situation, E.On’s 12 month v10 fix ends this coming Tuesday, April 15. It offered customers a typical bill of £1,665 per year, but those moving onto the price cap will be made to pay £184 more unless they fix again.

Right now, according to Martin Lewis’ MSE, the cheapest fixes available are from Outfox The Market, at 16.2% lower than the current April to July price cap, Octopus Energy, at 14.6% lower. E.On also has a deal at 12.8% lower including cashback from MSE if you use its Cheap Energy Club comparison tool.

A saving of 16.2% would equal a very handy £299 lower than the current price cap.

Of course, the price cap is not a cap on bills - it's a cap on the unit rates, so if you use more, you'll pay more. The £1,849 figure, as well as the illustrations for different fixes, are estimates based on a typical average-use household worked out by using the unit rate prices.