At a glance
The short answer: compare the whole tariff, not the label
A fixed gas tariff keeps its unit rate and standing charge unchanged for an agreed term. A variable tariff can change its rates, although a default tariff in England, Scotland or Wales is protected by Ofgem’s price cap. Neither option caps the amount you pay: using more gas still increases the bill.
The useful comparison is (annual gas kWh × unit rate) + (365 × daily standing charge) + unavoidable fees. Use the annual consumption on a recent statement, not the monthly Direct Debit. A fix can provide budget certainty, but it is not automatically cheaper than a variable deal and may charge an exit fee if you leave early.
Ofgem regulates Great Britain’s market. Northern Ireland has a separate regulator, tariff system and more limited choice of gas supplier, covered below.
What fixed and variable actually mean
On a fixed tariff, the price for each kWh and the daily standing charge normally stay the same until the contract ends. Your payment is not fixed. A colder winter, longer heating hours or an estimated bill corrected by an actual reading can still change what you owe. Check whether both fuels are fixed on a dual-fuel offer and whether any discount has conditions.
A variable tariff has no fixed end date and its rates can move. In Great Britain, the price cap limits unit rates and standing charges on default tariffs, but the cap is reviewed every three months and is not a maximum annual bill. A supplier can also offer other variable tariffs with their own terms, so confirm whether an offer is the default capped tariff.
From 1 October to 31 December 2026, Ofgem’s Great Britain average Direct Debit gas cap rate is 7.97p per kWh with a 29.68p daily standing charge, including 5% VAT. Rates vary by region and payment method. Treat these as a current benchmark, not a quote.
Calculate the annual cost of each gas tariff
Find your annual gas consumption in kWh on a bill or online account. If it is unavailable, add a complete year of billed kWh; do not add raw meter units. Then apply each offer’s VAT-inclusive unit rate and standing charge. Our gas units to kWh guide explains why meter units and billed kWh differ.
For a fair comparison, use the same annual consumption and number of days for both tariffs. Add a required membership fee or exit fee only when it is relevant to your likely decision. Subtract guaranteed discounts, but do not count a conditional reward unless you expect to meet its terms.
The formula is: annual cost = (annual kWh × unit rate in pounds) + (daily standing charge in pounds × 365) + fees − guaranteed discounts. Use the gas bill calculator for a shorter billing period based on two meter readings and your exact rates.
- Usage: annual gas kWh from an actual bill or statement.
- Rates: unit rate and standing charge, checked on the tariff information label.
- Terms: end date, exit fee, payment method and any smart-meter condition.
- Support: confirm that any help you rely on will continue after switching.
Worked example: a cheaper unit rate can offset a higher daily charge
Suppose a household uses 10,000 kWh of gas a year. Tariff A uses the current Great Britain average capped Direct Debit gas rates: 7.97p per kWh and 29.68p per day. Tariff B is an illustrative fixed offer at 7.55p per kWh and 35p per day, with a £75 exit fee. It is not a real supplier quote.
Tariff A costs (10,000 × £0.0797) + (365 × £0.2968) = £905.33 a year. Tariff B costs (10,000 × £0.0755) + (365 × £0.35) = £882.75 a year. The fixed offer is £22.58 cheaper if the household stays for the comparison year and rates do not otherwise change.
The fixed tariff’s standing charge costs £19.42 more a year, while its unit rate saves 0.42p per kWh. Dividing £19.42 by £0.0042 gives a break-even point of about 4,623 kWh. Above that use, tariff B is cheaper on these two charges; below it, tariff A is cheaper. Paying the £75 exit fee would erase the example saving, which is why likely moving or switching plans matter.
| Cost item | Variable tariff A | Fixed tariff B |
|---|---|---|
| Unit rate | 7.97p/kWh | 7.55p/kWh |
| Standing charge | 29.68p/day | 35p/day |
| Usage charge | £797.00 | £755.00 |
| Annual standing charge | £108.33 | £127.75 |
| Annual total before exit fees | £905.33 | £882.75 |
Tariff B is invented to demonstrate the method. Tariff A uses Ofgem’s average Great Britain Direct Debit gas cap rates for 1 October to 31 December 2026.
Five checks before choosing a fixed deal
First, compare the offer with your current tariff and other available deals using the same annual kWh. Ofgem lists accredited comparison services, but some tariffs may need to be arranged directly with a supplier. Save the tariff information label or quote so you can check what was promised.
Second, consider how long you can realistically keep the tariff. Citizens Advice says a customer on a fixed tariff in Great Britain can switch without an exit fee when 49 days or less remain. With 50 days or more, an exit fee may apply. The fee and whether it is charged per fuel belong in the contract terms.
Third, check payment and meter requirements. A deal may require Direct Debit, online account management or a compatible smart meter. Fourth, look at customer service and any support you use, including the Priority Services Register or Warm Home Discount participation. Fifth, remember that a forecast saving is not guaranteed: future variable rates can rise or fall.
What happens when you switch supplier
Ofgem says a domestic supplier switch in Great Britain should take up to five working days. The new supplier arranges the transfer and there should be no interruption to the gas supply. Give an accurate opening reading when requested and keep a dated photo if it is safe to take one; the old supplier uses the agreed reading for the final bill.
A new domestic contract has a 14-day cooling-off period. Keep paying the old supplier until the final account is settled, then check the closing reading and any credit. Our credit refund guide explains the Great Britain final-bill and refund deadlines.
Debt, prepayment arrangements, a landlord-controlled supply or a specialist meter can affect the available choices. Do not use a saving estimate as a reason to ignore arrears or cancel a payment without agreement; speak to the supplier about an affordable plan.
Northern Ireland tariffs and switching are different
Ofgem’s price cap and switching rules do not apply in Northern Ireland. The Utility Regulator approves maximum tariffs for regulated domestic gas suppliers, and supplier choice depends on the network area. Its consumer guidance says gas customers can choose between suppliers only in Greater Belfast; use the Consumer Council’s independent comparison tool for the options actually available at your address.
Northern Ireland contracts can include cancellation charges. The Utility Regulator says to check the tariff length, fixed or variable rates, discounts and early-exit terms before signing. Its published switching guidance describes a cooling-off period of up to ten working days and a different switching timetable, so do not assume the Great Britain 14-day and five-working-day rules apply.
Frequently asked questions
Is a fixed gas tariff always cheaper than a variable tariff?
No. A fix provides stable unit and standing-charge rates for its term, but the starting prices may be higher or lower. Compare the full annual cost using your own gas kWh and include relevant fees.
Does fixing my tariff fix my monthly gas bill?
No. It fixes the tariff rates, not consumption. Your bill or Direct Debit can change if you use more gas, an estimate is corrected or the supplier reviews the payment plan.
Can I leave a fixed energy tariff without an exit fee?
In Great Britain, Citizens Advice says you can switch without an exit fee when 49 days or less remain on the fixed contract. Earlier switches may carry the fee shown in your terms. Northern Ireland arrangements differ.
Does the energy price cap protect a fixed tariff?
The Ofgem cap applies to default tariffs in England, Scotland and Wales, not an agreed fixed tariff. It limits rates rather than the total bill and does not apply in Northern Ireland.
What usage figure should I enter when comparing tariffs?
Use annual gas consumption in kWh from a recent bill or statement. Do not use the monthly Direct Debit or raw cubic-metre or cubic-foot meter units.
Sources
Rates and rules checked on 16 October 2026. Time-sensitive figures should be checked again before use.