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Compare the whole tariff, not its label. Use your household’s annual electricity and gas consumption, each fuel’s unit rate, each daily standing charge, the contract length and any exit fee. A fixed tariff keeps those agreed rates stable for the term, but it does not freeze your total bill. A standard variable tariff can change, while its covered rates are limited by Ofgem’s price cap. Either option can cost less or more depending on future rates and how much energy you use.
What “fixed” and “variable” mean
Fixed tariffs hold the rates, not your bill
On a fixed energy contract, the supplier agrees a unit rate for electricity, a unit rate for gas and daily standing charges for a stated term. Citizens Advice Wales describes it this way: “A fixed tariff charges you the same rate for your gas or electricity and your standing charge, until your contract ends.”
Your meter readings still determine the bill. If you use more kilowatt-hours (kWh), you pay for more kWh; if you use less, the usage portion falls. A cold winter, a new appliance or a change in occupancy can therefore make the total bill rise even while every tariff rate remains unchanged.
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsStandard variable tariffs can change
A standard variable tariff (SVT) has rates that the supplier may change. For default tariffs covered by Ofgem’s rules, the price cap limits the maximum unit rates and standing charges the supplier can charge for the relevant region, payment method, fuel and meter type. The cap does not apply to fixed tariffs.
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A variable customer can benefit if the supplier reduces rates, but a reduction is not guaranteed. Rates can also rise when the cap or the supplier’s capped prices change. The cap constrains the rate, not the amount a particular home spends.
| Comparison point | Fixed tariff | Standard variable tariff |
|---|---|---|
| Unit rates and standing charge | Set for the agreed term, subject to the written contract | Can change; covered default-tariff rates are limited by Ofgem’s cap |
| If market-linked costs rise | Your contracted rates normally stay in place during the term | Your rates may rise, subject to the cap and supplier rules |
| If market-linked costs fall | You continue paying the contracted rates | Your supplier may lower the tariff, but is not required to match every market move |
| Leaving early | An exit fee may apply; check the contract and remaining term | There is no fixed-term termination fee, but check notice and account conditions |
| Useful cost input | Your expected annual kWh multiplied by the fixed rates, plus 365 days of charges and any relevant fee | Your expected annual kWh and current rates, tested against possible later rate changes |
This table describes the mechanics, not a forecast. No tariff type is automatically the cheapest.
What Ofgem’s price cap does—and does not—do
Ofgem updates the cap every three months. At the time covered here, the published period was 1 October to 31 December 2026. Exact capped rates vary by region, payment method, fuel and meter type, so use Ofgem’s current table for your circumstances rather than an old national figure.
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The cap limits the unit rates and standing charges on covered default tariffs. It does not set a maximum total bill. Ofgem puts it plainly: “It does not limit the cost of your total bill. The more energy you use, the higher your bill will be.” A household using twice as many kWh as another household can therefore pay roughly twice the usage component even when both are on the same capped rate.
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Standing charges apply every day
A standing charge is a daily amount for keeping the connection and account available. It is charged on days when you use no electricity or gas, so unit-rate comparisons alone can be misleading. The charge has a larger effect on a low-use home because fewer kWh share the fixed daily cost.
For context, the House of Commons Library reported 2026 Great Britain average direct-debit standing charges under the October–December cap of 54.8 pence per day for electricity and 29.7 pence per day for gas, or 84.5 pence per day combined. That is an average reference, not a quote for every region, payment method or meter. The same source estimated standing charges at about 18% of a typical dual-fuel bill under the Q4 2026 cap; the percentage is not universal.
Ofgem’s medium typical domestic consumption values cited by the House of Commons Library are 2,500 kWh of electricity and 9,500 kWh of gas per year. They are reference values for comparisons, not a substitute for your own meter history.
How to calculate the cost of each offer
Build the comparison from annual usage and tariff components. Do the calculation separately for electricity and gas, then add the two results for a dual-fuel home.
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- Collect your usage. Use a recent 12-month statement or meter history for electricity kWh and gas kWh. If your household has changed, note why the old year may not represent the next one.
- Record every tariff rate. Write down the electricity unit rate, gas unit rate, electricity standing charge and gas standing charge, with the applicable VAT or billing basis shown by the supplier.
- Calculate each fuel’s usage cost. Multiply annual electricity kWh by the offered electricity unit rate. Repeat for gas.
- Calculate standing charges. Multiply each daily charge by 365 days. If a tariff has different charges for different periods or meter registers, calculate each period separately.
- Add the components. Electricity usage cost + electricity standing charges + gas usage cost + gas standing charges gives an annual tariff estimate before one-off adjustments.
- Include an exit fee when relevant. If switching would end an existing fix early, add the stated termination fee to the cost of leaving. Do not include a fee that does not apply under the contract.
- Compare like with like. Keep region, payment method, meter type, fuels, contract term and any time-of-use periods consistent between offers.
In spreadsheet form, the core formula is:
annual estimate = (electricity kWh × electricity unit rate) + (gas kWh × gas unit rate) + (365 × electricity daily charge) + (365 × gas daily charge) + applicable exit fee
For a single-fuel home, omit the other fuel. For a tariff with rates that vary by time of day, replace the single unit-rate multiplication with one calculation for each time band and use your consumption in that band.
Why the monthly direct debit is not the tariff price
A quoted monthly direct debit is a payment arrangement. The supplier sets it from expected annual costs and may adjust it to manage a credit or debit balance. Two suppliers can quote different monthly payments for similar rates, and a payment can be too high or too low if your usage changes. Compare the underlying unit rates and standing charges, then treat the direct debit as a cash-flow figure.
Use scenarios for a variable tariff
A variable estimate uses today’s rates, but those rates can change. Create at least two clearly labelled scenarios in your worksheet: one in which current rates remain unchanged and another in which they change at a future review. Do not present either scenario as a prediction. A fixed tariff can be compared with each scenario to show the value of certainty and the cost of giving up potential falls.
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Costs and risks you are actually trading
Price certainty versus flexibility
Fixing buys a known rate for the agreed period. That can make budgeting easier when a sudden rate increase would be difficult to absorb. The trade-off is that you may be unable to benefit from lower variable rates without paying to leave the contract.
Staying variable preserves the ability to switch without a fixed-term exit fee and lets you benefit if your supplier lowers rates. The trade-off is exposure to rate changes and less certainty about future bills.
Consumption risk remains in both choices
Neither contract protects you from using more energy. Insulation work, a new electric vehicle, working from home, a medical device or a vacant property can materially change kWh. Re-run the calculation when your expected annual use changes rather than relying on a previous “typical” figure.
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Contract-term risk
A longer fix can provide certainty for longer, but it can also lock you into rates that become uncompetitive before the end date. Check the end date, renewal process and notice requirements before accepting. A tariff that looks attractive for its first year may be less suitable if the remaining term prevents a later switch.
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Regional and payment differences
Cap levels and supplier rates depend on where you live and how you pay. A direct-debit quote cannot be assumed to apply to a prepayment meter or another payment method. Enter the correct postcode, meter type and payment method when requesting an offer.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When a fixed tariff may fit—and when variable may fit
A fix may suit you if
- Your budget cannot easily absorb a rate increase during the proposed term.
- The fixed unit rates and standing charges produce an acceptable estimate using your own kWh.
- You expect to stay at the property until the end date, reducing the chance of an early exit.
- You have checked the exit fee, renewal terms and whether the tariff includes both fuels you need.
An SVT may suit you if
- You value the ability to switch without a fixed-term termination charge.
- You can tolerate changing bills and keep enough budget headroom for a rise.
- The available fixed offers are materially above the current variable estimate and do not provide enough certainty to justify the difference.
- You may move home, change meter type or otherwise need flexibility before a fixed term would end.
These are decision conditions, not personal advice. The right choice depends on your usage, finances, expected time at the property and tolerance for price changes.
How to switch without an avoidable charge
- Find your current documents. Note the tariff name, unit rates, daily charges, annual consumption, payment method and meter type.
- Check the fixed-term end date. If the contract is fixed, find the written exit-fee amount and the rules for switching near the end.
- Calculate the remaining-contract cost. Compare the potential saving from the new tariff with any fee and with the cost of staying until the end date.
- Check the new offer’s full terms. Confirm both fuels, rates, standing charges, term, payment method, meter requirements, discounts and any exit fee.
- Submit the switch through the supplier or a comparison website. The UK Government describes comparison websites as third-party intermediaries and warns that conflicts of interest, opaque contracting and mis-selling are possible. Verify the underlying supplier contract rather than relying only on a headline result.
- Keep readings and confirmation. Record meter readings on the agreed switch date and retain the confirmation, tariff terms and final bill from the old supplier.
Ofgem says a home-energy switch generally completes within five working days, although account or meter issues can affect an individual case.
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The 49-day rule for fixed contracts
Citizens Advice says a supplier may charge an exit fee when 50 or more days remain on a fixed contract. Customers in the final 49 days can switch without an exit fee. Treat this as guidance, not a substitute for your contract: check the supplier’s written terms and confirm the fee before submitting a switch. Ofgem also warns that leaving a fixed tariff before its end may incur an exit fee.
Common comparison mistakes
- Using a “typical annual bill” as your personal maximum. It is a reference consumption profile, not a cap on what your home can pay.
- Comparing unit rates but ignoring standing charges. A low-use household can be disproportionately affected by daily charges.
- Comparing monthly payments. Direct debit reflects expected costs and account-balance management, not just the tariff rate.
- Assuming fixed means bill-fixed. Consumption still drives the total.
- Treating a forecast as fact. Future variable rates and your future kWh are uncertain.
- Leaving a fix without checking the fee. A fee can erase an apparent saving.
- Mixing incompatible offers. Check region, payment method, meter, fuels, term and time-of-use periods.
- Relying on an old cap figure. Ofgem reviews the cap quarterly; use the current period’s data.
Standing-charge policy is not the same as a tariff offer
Ofgem has listed proposals and consultations about lower-standing-charge designs, including a zero-standing-charge cap variant. Those are policy developments, not proof that a zero-standing-charge tariff is currently available to every household. Check the current status and the actual supplier terms before basing a decision on them.
A practical decision checklist
- Have you used your own last-12-month electricity and gas kWh?
- Are both unit rates and both daily standing charges recorded?
- Are the region, payment method and meter type the same for every offer?
- Have you checked the fixed term, end date, renewal process and exit fee?
- Did you separate the tariff estimate from the monthly direct-debit amount?
- For a variable option, did you model more than one possible rate outcome without calling it a forecast?
- Can your budget absorb a rise, or is certainty worth paying for?
- If you may move or change your meter, does the contract allow a practical exit?
Bottom line
A fixed contract is a price-certainty product, not a guaranteed saving. A standard variable tariff offers flexibility but leaves you exposed to rate changes within the price-cap framework. Calculate both using your actual annual kWh, add every daily standing charge and any applicable exit fee, and then choose the risk level your household can afford. Recheck the figures when Ofgem’s quarterly cap changes or your consumption pattern changes.
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