Energy tariff comparison calculator
Two deals side by side, using your own usage and the rates from your bill. It handles standing charges and Economy 7 properly, shows the usage level at which one deal overtakes the other, and works out how far the price cap would have to move before a fixed deal stops being worth it.
Your usage
These figures are on your annual statement. If you cannot find them, your supplier's app usually shows the last twelve months.
Deal 1 — what you pay now
Deal 2 — the one you are considering
Your result
How this is worked out
Every energy tariff has two parts, and comparing only one of them is the commonest mistake. The unit rate is what you pay per kWh used. The standing charge is a daily fee you pay whether you use anything or not.
annual cost = (usage × unit rate) + (standing charge × 365)
All rates in pence, so divide by 100 for pounds.
Economy 7 splits the usage across a day rate and a night rate.
Why the break-even point matters
A deal with a lower unit rate but a higher standing charge only wins above a certain level of usage. Below it, the standing charge dominates and the apparently more expensive deal is cheaper.
That crossover is worth knowing because your usage varies year to year. If your consumption sits close to the break-even point, the two deals are effectively equivalent and the choice can be made on other grounds. If you are well past it, the decision is clear.
break-even usage = (standing A − standing B) × 365
÷ (unit rate B − unit rate A)
Exit fees, and when you can avoid them
Leaving a fixed deal early usually costs a fee, commonly in the region of £25 to £35 per fuel. But suppliers are not allowed to charge one in the final 49 days of a fixed term, so if your deal is close to ending, waiting a few weeks can save the fee entirely. It is worth checking your end date before paying to leave.
Fixing against a capped tariff
Fixing is a bet about the future, and nobody knows where the cap will go. So rather than pretending to predict it, this works the question backwards: it tells you how far the variable rates would have to move before the fixed deal stopped being the better choice.
That converts an impossible forecast into a judgement you can actually make. "Rates would need to rise 8% for this fix to pay off" is something you can weigh against what you have been reading. "Rates would need to fall 3% before this fix becomes a mistake" tells you the fix is already ahead and has a margin of safety.
What this assumes
- Your usage next year matches what you have entered. It rarely matches exactly, which is why the break-even figure is more useful than the headline saving.
- A 365-day year. In a leap year suppliers charge the standing charge for the actual days in the period, so a leap year costs one extra day per fuel.
- Rates stay as entered for the whole period. A capped tariff will change at the next quarterly review.
- A flat rate per unit, or a simple day and night split. It does not model time-of-use or agile tariffs where the price changes through the day.
- Rates and standing charges vary by region, since network costs differ across the fourteen distribution areas. Use the figures on your own bill rather than a national average.
- Payment method matters. Compare like with like, since a quote for direct debit is not comparable with a standard credit or prepayment rate.
Things that will make this comparison wrong
A unit rate and a standing charge describe most tariffs well, but not all of them. Check for these before trusting the answer:
- Conditional discounts. Reductions that only apply if you pay by direct debit, choose paperless billing, or stay a certain length of time.
- Welcome credits. A lump sum paid into your account reduces the first year but not the ongoing rate, so it flatters a deal you may not stay on.
- Tiered rates. A few tariffs charge one rate for the first block of units and another beyond it, which a single unit rate cannot represent.
- Bundled extras. Boiler cover or similar services add value and cost, and are not comparable on rates alone.
- Solar export. If you export electricity, your net bill depends on the export tariff too, which this does not model.
- Warm Home Discount. If you are eligible, it is a rebate rather than a change to your rates, so it applies whichever deal you choose and should not sway the comparison.
Where this stops being reliable
This compares the tariffs you enter, nothing more. It does not know which deals are available to you, does not search the market, and takes no commission from anyone. It also cannot judge a supplier's service, which matters more than a few pounds a year when something goes wrong. Check the rates against your actual bill or quote before switching, since a mistyped standing charge changes the answer substantially.
What this is, and what it is not
This is a calculator, not a comparison service. It does not list available tariffs, does not search the market, does not recommend a supplier and cannot switch you to anything. Nobody pays to appear here, because there is nothing to appear on. Ofgem's Confidence Code, which accredits price comparison services, applies to sites that let you compare and switch to actual tariffs rather than to standalone calculators like this one.
If you want to see what deals are available to you, use an Ofgem-accredited comparison service. Use this to check the arithmetic on whatever they, or your supplier, put in front of you.
Where the default figures come from. The usage figures suggested above are Ofgem's Typical Domestic Consumption Values, which the industry uses for illustrative comparisons. They were last revised with effect from 1 July 2026. Every rate is entered by you, so no tariff or price cap data is stored on this site.
Sources: Ofgem review of typical domestic consumption values · Ofgem on the price cap and standing charges · Ofgem on switching and exit fees