Should I fix my energy price?

A fixed tariff can leave you paying more even if energy prices rise. It depends how far they rise, when it happens and how long the increase lasts. In the Octopus example below, a 20% rise lasting from January to March is not enough to recover the extra cost of fixing for a year.

The price of fixing for a year

This comparison uses Octopus’s published London rates on 14 October 2026: its twelve-month fix and Flexible Octopus, paid by Direct Debit. It assumes 2,500 kWh of electricity and 9,500 kWh of gas over the year. Prices elsewhere, and offers from other suppliers, will differ.

If variable prices stayed unchanged before tax, the bill for 14 October 2026 to 13 October 2027 would be £1,716 on Flexible or £1,883 on the fix. The £167 difference is what future price rises have to outweigh before this fix saves money. About £103 of that premium comes from gas, with the rest from electricity.

Both bills include the scheduled return of 5% electricity VAT in April. Electricity currently has no VAT until 31 March 2027; gas still has 5%. A fixed tariff protects against changes in the underlying rates, not a change in the tax charged on them.

How far would variable prices have to rise?

In 2025, households bought 44% of their annual gas in January–March and just 8% in July–September. Electricity varied less across the seasons. We use those national consumption patterns to calculate how much energy each price change affects.

A 20% increase for January–March adds about £107 to the variable bill. That is still less than the £167 premium for fixing the whole year. Keeping the increase for the rest of the contract adds £212 instead, enough for the fix to win.

For this household, both unit prices would need to rise by about 31% for January–March alone, or 16% from January to the end of the contract, for fixing to break even.

Gas and electricity need not move together. If only gas rises by 20% for January–March, the extra variable cost is about £69 and the fix remains £98 dearer. A forecast of a 20% increase in the overall price-cap headline cannot simply be applied to every rate in the tariff.

Your annual gas and electricity use, in kWh, is on your bill or in your online account. The calculator lets you use those totals. For electric heating, an EV, solar panels or a home that is empty for part of the year, the national seasonal pattern may be a poor fit. The comparison then needs your monthly consumption, including separate peak and off-peak use where relevant.

What if a higher winter bill would be unaffordable?

Fixing protects against an increase in the tariff even when it does not produce the lowest eventual bill. In this example, that protection costs £167 over the year if variable prices stay unchanged: about £14 a month. For a household unable to meet a sharp price rise, limiting that risk can be worth the extra cost.

The extra £14 is only an average for the year, not a promise about monthly Direct Debits. A fix sets the tariff’s underlying unit rates and standing charges. A cold winter can still increase consumption and the total bill; tax can change too. The fixed bill itself must still be affordable.

Variable tariffs below the price cap

Some variable tariffs are already priced below the cap. E.ON Next Pledge, for example, currently discounts the cap’s unit rates by an amount worth £50 a year at its standard dual-fuel usage. Its rates can still rise or fall. At that same standard usage, a fix advertised as £30 below the cap would start £20 dearer than this variable alternative. The difference for your own consumption could be larger or smaller. Next Pledge also charges £25 per fuel to leave for another supplier, while a switch to another E.ON Next tariff is free.

Fixed and variable quotes need to use the same postcode, payment method and annual consumption. A lower Direct Debit can simply mean the supplier has estimated that you will use less energy. Comparing the unit prices and standing charges avoids that problem; fixing does not cap your total bill.

What if a cheaper deal appears later?

The Octopus fix lists an early exit fee of £50 per fuel: £100 for both. Check whether it would apply to the switch you want to make. If it does, a later tariff saving £80 over the remaining contract period would leave you £20 worse off after the fee. A £150 remaining saving would leave you £50 better off.

That fee is not added to the table because the table assumes you stay for the year. If you must pay to leave your current tariff now, add that charge to the new fix’s cost. And compare a two-year offer over two years: one winter’s forecast cannot establish whether its second year is good value.