Households across the UK face a collective price hike of £42 million this month as a number of fixed energy deals come to an end.
With 61 fixed deals from 13 suppliers ending this month, up to 193,000 energy customers are set to see their bills soar if they don't switch away from their expiring energy tariffs.
Those on fixed deals ending soon could see an increase of an average £216 if they allow their energy supplier to place them on a standard tariff after the fixed deal ends. Some unlucky customers could even see price hikes of up to £362.
Standard variable tariffs (SVTs) are typically the most expensive type of energy plan, and in most cases customers will be 'rolled onto' these tariffs once their fixed plans end if they don't shop around for a better deal.
Standard variable tariffs or default tariffs became even worse value recently, after many suppliers raised their prices after Ofgem's price cap was increased.
The energy price cap sets an upper limit for default tariffs, and this limit was raised by 10% in April to £1,254 per year - that's £381 more than the cheapest energy deal on the market today.
Sarah Broomfield, energy expert at Uswitch, said: "The huge growth in switching means more and more customers are taking the power into their own hands and saving hundreds of pounds a year on their energy bills.
"But with standard tariffs having skyrocketed after the price cap was increased by a monstrous 10% in April, households whose fixed deals are ending could see their bills increase by as much as £360 a year if they roll onto their supplier's standard plan."
There's no exit fee for energy plans ending in the next 49 days, so households on energy tariffs ending soon can switch and save now without having to pay their supplier a charge for leaving early.
Uswitch's energy expert said: "With 30 deals priced below £1,000 a year, not to mention plenty of tariffs from challenger brands offering strong customer service, renewable energy, and online account management, now is the time to lock in a cheap fixed deal before wholesale costs start to increase and push prices back up again."