The short answer. On 29 October 2026 we opened 21 free UK appliance running cost calculators and checked the electricity rate each one uses before you type anything in. Only 3 started from the current Ofgem price cap of 26.32p per kWh. The rest used rates from earlier in 2026, from 2023, and in one case 14.9p. The sums were right in every calculator we could run. The rate was the problem, and most people never change it.
The best free calculator for most people is Calks.uk: current rate, date shown, nothing to sign up for. Look Into publishes one of the three that passed, so we have scored our own calculator on the same rules but left it out of the numbered list.
A running cost calculator does one sum: watts × hours ÷ 1,000 × the price of a unit of electricity. A 2,000W heater on for one hour uses 2 kWh, which costs 52.64p at 26.32p. Every tool that returned an answer got that arithmetic right. What changes the answer is the number in the rate box, and that number goes out of date four times a year when Ofgem resets the price cap. A calculator still set to 24.5p tells you the same heater costs 49p an hour, about 7% less than it does. One still set to 14.9p tells you 30p, 43% less.
This page carries no affiliate links and recommends no product. Nobody paid to be included, and none of the tools listed was told in advance.
Prices and specs last checked by Look Into on 29 October 2026 · next check 4 January 2027 · how we picked
What 21 calculators use as their starting rate
Each tool was opened on 29 October 2026, when the cap for 1 October to 31 December 2026 was in force. Where a page showed or prefilled a rate, we recorded it exactly. Where we could run the standard test (2,000W for one hour, expected 52.6p), we did.
| Calculator | Starting rate as shown | Current cap? | Date shown | 2kW for 1 hour |
|---|---|---|---|---|
| Look Into appliance running cost calculator | 26.32p, editable | Yes | 23 Oct 2026 | 52.6p |
| Calks.uk electricity cost calculator | 26.32p, editable | Yes | Rates verified 20 Oct 2026 | £0.53 |
| Chefspick appliance electricity cost calculator | Page text cites 26.32p; field default not visible | Yes (text) | 6 Oct 2026 | Not run (security prompt) |
| Smart Energy GB energy cost calculator | Not shown; says it reflects the 1 October 2026 cap | Not shown | 1 Oct 2026 | Not possible (no wattage input) |
| Citizens Advice appliance calculator | Not shown before the second step | Not shown | None | Not run (multi-step form) |
| Uswitch room-by-room appliance calculator | Not shown; says it uses the current cap | Not shown | 1 Jul 2026 | Not run |
| Selectra your-rate calculator | 26.11p, labelled "Ofgem price cap, 1 July to 30 September 2026" | No | Rate period shown | £2.11 for 4 hours at 26.32p (52.6p an hour) |
| iForge Apps electricity cost calculator | 26.11p, described as "current" | No | Last checked 19 Jun 2026 | Not run |
| Centre for Sustainable Energy table | 26p, "as of July 2026" (a table, not a calculator) | No | July 2026 | Not applicable |
| sum.money energy cost calculator | 27.69p, "Ofgem cap Q1 2026" | No | None | Not run |
| The Energy Shop energy cost calculator | 24.96p prefilled | No | None | £0.53 |
| ClearCost UK appliance energy cost calculator | 24.67p, "Ofgem price cap from April 2026" | No | April 2026 | Not run |
| UK Calculator electricity usage calculator | 24.5p, "Ofgem cap Q1 2026" | No | February and April 2026 (both shown) | Not run |
| HeatWise Home appliance running cost calculator | £0.25 | No | 28 Apr 2026 | Not run |
| Future plc comparison widget (used on Ideal Home and GoodTo) | 30p, the energy price guarantee rate, which ended in 2023 | No | None | Not run |
| m0ukd electricity cost calculator | None; worked example uses 22.19p | No | © 2007 to 2017 | Not run |
| The Calculator Site electricity calculator | None; examples in dollars | No | 20 May 2025 | Not run |
| WeCovr appliance energy cost calculator | None shown | No | None | Not run |
| usave energy cost calculator | None stated | No | 2 Jul 2021 | Not run |
| UKPower electricity cost calculator | Blank; presets fill 14.9p | No | None | No result when values were typed in |
| Consumer Council (Northern Ireland) appliance cost checker | 32.150p, the Power NI tariff | Not applicable (NI is outside the GB cap) | None | Not run |
On UKPower, typing a wattage, hours and rate by hand produced no result in our checks: the page calls a calculation function, calcwattchecker, that was not defined when we loaded it. Picking one of its preset appliances did calculate, using 14.9p.
How we ranked them
Every tool had to be free, give a result without an account or email address, work for Great Britain tariffs or let you type a GB rate, and have a named publisher with a contact route. We then scored each out of 100.
- Starting rate (30 points). 30 if it starts at the current cap. 15 if it shows an older rate you can change. 10 if the rate is hidden. 0 if it is stale and fixed.
- Test result (20 points). 20 if the 2kW test came out right, 10 if we could not run it, 5 if it has no wattage input, 0 if it failed.
- Range (20 points). How many appliances it covers and whether you can enter your own wattage.
- Shows its rate and date (15 points). 15 for both, 8 for one, 0 for neither.
- Friction (15 points). Points off for extra steps, security prompts and sales nudges.
| Calculator | Rate /30 | Test /20 | Range /20 | Rate and date /15 | Friction /15 | Total |
|---|---|---|---|---|---|---|
| Calks.uk | 30 | 20 | 14 | 15 | 15 | 94 |
| Selectra | 15 | 20 | 14 | 15 | 15 | 79 |
| Chefspick | 20 | 10 | 10 | 15 | 6 | 61 |
| The Calculator Site | 10 | 10 | 18 | 8 | 15 | 61 |
| The Energy Shop | 15 | 20 | 12 | 0 | 11 | 58 |
| Uswitch | 10 | 10 | 14 | 8 | 15 | 57 |
| Centre for Sustainable Energy | 5 | 10 | 10 | 15 | 15 | 55 |
| Citizens Advice | 10 | 10 | 20 | 0 | 9 | 49 |
| Smart Energy GB | 10 | 5 | 8 | 8 | 15 | 46 |
| UKPower | 0 | 0 | 12 | 0 | 11 | 23 |
| Look Into (not ranked) | 30 | 20 | 14 | 15 | 15 | 94 |
These scores reward a calculator you can trust without checking it. That is why Citizens Advice, which has the widest appliance list and the most trusted name of any tool here, sits eighth: it does not show its rate until you are part way through, so we could not see it without submitting the form. If you already know your own unit rate, it is an excellent tool.
The 10 best free running cost calculators
1. Calks.uk electricity cost calculator
Best for most people. It opens at 26.32p, says its rates were verified on 20 October 2026, and gives daily, weekly, monthly and yearly costs from a wattage and hours a day. There are 16 preset appliances. It is a small independent site run by a named individual, and it rounds to whole pence, so a phone charger shows as 0p.
2. Selectra your-rate calculator
Best layout. Fifteen preset appliances, uses per week, and a clear cost per use, day, month and year. It also labels its rate honestly: "Ofgem price cap, 1 July to 30 September 2026". That is last quarter's 26.11p, so overwrite it with 26.32p or your own rate before you start.
3. Chefspick appliance electricity cost calculator
Current, with a hurdle. The page cites the 26.32p cap and was updated on 6 October 2026, but a sum-style security prompt sits between you and the answer, and we could not see the field's default without answering it.
4. The Calculator Site electricity calculator
Biggest preset list. Around 35 appliances. It is not built for the UK, its examples are in dollars and it shows no default rate, so type 26.32 in pence yourself.
5. The Energy Shop energy cost calculator
Works, but check the rate. Twelve presets and a correct answer on our test, but it prefills 24.96p, which matches no cap this year, and it shows a "cheapest tariff" figure alongside the result.
6. Uswitch room-by-room calculator
Best for a whole-house picture. Pick appliances room by room and see which rooms cost most. It says its costs use the current cap but does not show the rate, and the page was last updated on 1 July 2026.
Uswitch appliance guide and calculator
7. Centre for Sustainable Energy: How much electricity am I using?
Best for checking what a device draws. Not a calculator but a table of 31 appliances with typical power and cost, priced at 26p "as of July 2026". Many other tools, ours included, use its wattage figures.
8. Citizens Advice appliance calculator
Widest list, most trusted. Pick from 40 appliances and compare up to 10. You can enter your own rate or use a national average, but the page does not show that average before the second step.
9. Smart Energy GB energy cost calculator
Quickest monthly picture. Sliders for nine everyday appliances and a comparison with the last two caps. It says it was updated for the 1 October 2026 cap but does not show the rate, and you cannot enter your own wattage.
10. Consumer Council (Northern Ireland) appliance cost checker
The one to use in Northern Ireland. The Ofgem cap does not apply in Northern Ireland, so GB calculators give the wrong answer there. This one uses the Power NI unit rate of 32.150p. We did not score it against the GB tools.
Consumer Council appliance cost checker
Our own calculator, judged on the same rules
The Look Into appliance running cost calculator starts at 26.32p, shows the rate and the date it was last updated, and scores 94 on the rules above, the same as Calks.uk. It is the only free calculator we found that models how much of the time a thermostat actually keeps a heater, blanket or dehumidifier running, and the only one with an Economy 7 option. Its weakness is range: it covers three kinds of appliance plus a custom option, not dozens. Its heater tab also starts with the heater running 60% of each hour, which gives 31.6p an hour for 2kW rather than 52.6p, so set the duty cycle to 100% if your heater has no thermostat. We have not given it a number because we cannot judge our own tool impartially.
How to get the right answer from any calculator
- Use your own unit rate. It is on your bill or app in pence per kWh. The cap is an average: regional rates and fixed tariffs differ.
- Find the real wattage. It is on the rating plate or in the manual. The Centre for Sustainable Energy table gives typical figures if you cannot find it.
- Allow for the thermostat. A 2kW heater with a thermostat does not draw 2kW all hour once the room is warm. A calculator that assumes it does will overstate the cost.
- Leave the standing charge out. You pay it whatever you switch on. At the October 2026 cap it is 54.83p a day for electricity. Our standing charge report has the figure for each region.
For cost per hour and per use of 26 common appliances at today's rate, already worked out, see the UK Running Cost Index. For what devices cost left on all year, see the Always-On Load Index.
Method
We searched for free UK appliance and electricity running cost calculators on 29 October 2026 and opened every tool we found from an identifiable publisher, 21 in all. For each we recorded the starting rate exactly as shown, any date on the page, and the result of a 2,000W, one-hour test where the tool allowed it. We typed values only into the calculators themselves. We did not submit multi-step forms, answer security prompts, sign up or give an email address, and we declined non-essential cookies where asked. The rate we compared against is the Ofgem price cap for 1 October to 31 December 2026, direct debit, Great Britain average: 26.32p per kWh, with no VAT on electricity from 1 October 2026 to 31 March 2027. Energy Saving Trust, MoneySavingExpert, Which?, Octopus, EDF, British Gas and OVO did not have a standalone appliance running cost calculator that we could find on that date.
We will run the same check again after the January 2027 cap takes effect on 1 January 2027 and record which tools updated.
Questions people ask
How do I work out what an appliance costs to run?
Multiply the wattage by the hours of use, divide by 1,000 to get kWh, then multiply by your unit rate. A 2,000W heater for one hour is 2 kWh, which costs 52.64p at 26.32p per kWh.
What rate should I use in a running cost calculator?
Your own unit rate from your bill. If you are on a standard variable tariff in Great Britain and pay by direct debit, the average cap rate for 1 October to 31 December 2026 is 26.32p per kWh.
Why do different calculators give different answers for the same appliance?
Mostly because they start from different rates. On 29 October 2026 we found starting rates from 14.9p to 30p among 21 free calculators. They also use different wattages for the same type of appliance.
Is there a running cost calculator for Northern Ireland?
Yes. The Consumer Council's appliance cost checker uses the Power NI unit rate. The Ofgem cap covers England, Scotland and Wales only.