Experts are urging Brits to "act now" ahead of a spike in energy bill prices from next month.
The average energy bill for a dual-fuel home paying by direct debit will increase from £1,738-a-year to £1,849 from April 1.
This follows today's higher-than-expected 6.4% increase in Ofgem's energy price cap - meaning the average bill rises by £111 a year.
Ofgem changes the price cap for households every three months, largely based on the cost of energy on wholesale markets.
The cap does not set the maximum a household will pay for their energy but limits the amount providers can charge them per unit of gas or electricity, so those who use more energy will pay more.
According to solar panel experts at Grant Store, millions of consumers risk overpaying unless they lock in a fixed-rate tariff before the increase takes effect.
They said: "This increase could add an extra £200 per year to energy bills for millions of consumers, making it crucial to take action now to avoid unnecessary overpayments.
"An estimated 80% of households in England, Scotland, and Wales are on price-capped variable tariffs, meaning the vast majority will feel the impact of this rise.
"Energy providers including British Gas, EDF, Octopus, and Ovo are expected to raise their rates accordingly. For many, this means higher monthly payments unless they secure a fixed deal now.
"While future predictions always carry some uncertainty, current indicators suggest the cap is unlikely to drop significantly for the rest of the year. Locking in a fixed tariff now could provide much-needed stability and protection against further increases.
"For those looking to avoid the hike, it's important to compare fixed-rate deals now. Using an Ofgem-accredited comparison tool will help find the best options, but speed is key -- deals that are available today might not be around much longer.
"Households should also consider other factors beyond price, such as customer service ratings, smart meter compatibility, and government scheme eligibility, before switching.
"With just over a month until the changes take effect, energy customers must act quickly to prevent unnecessary costs. Fixed-rate tariffs won't be right for everyone, but for many, securing a deal now could provide instant savings and long-term financial security."