Defaults last checked: October 29, 2026.
Most energy decisions come down to a handful of numbers: what you pay per kWh, how much energy something uses, and what it costs up front. These calculators do that arithmetic for you, in your own currency, and they show their working.
Each one starts with default values for the United States, the United Kingdom, Australia, Canada or the eurozone. Every default comes from a public source, such as the U.S. EIA, Ofgem’s price cap, Eurostat, Victoria’s Essential Services Commission or the EU’s PVGIS solar model, and the source and date sit right under the calculator. Where we couldn’t find a figure we trust, the field is left empty and you fill it in. Your own bill is always better than an average, so change anything that doesn’t match your home.
The calculators
Is switching worth it?
Compare what you use now with what you’d use after a change, such as an old fridge for an efficient one or a gas boiler for a heat pump. You get the yearly saving, simple payback and the result over ten years.
Solar panel payback calculator
Estimate yearly generation from your system size and local yield, split it between what you use and what you export, and see how long the panels take to pay for themselves.
Portable power station calculator
List the appliances you want to keep running in an outage and find out how long a given power station lasts, what capacity you need, and how the cost per kWh compares with a fuel generator.
Home battery payback calculator
Work out what a home battery saves by storing surplus solar or by charging on a cheap rate and covering the evening peak.
Heat pump vs gas or oil calculator
Turn your current gas or oil use into the heat your home needs, then see the running cost with a heat pump and the efficiency it must reach to come out cheaper.
Smart thermostat savings calculator
A quick estimate of what a smart thermostat might save on your heating and cooling bill, and how fast it pays back.
Appliance running cost calculator
Watts × hours × price, with standby included. Useful for heaters, dehumidifiers, games consoles and anything else with a plug.
How we build them
The formulas are simple on purpose. Each calculator has a “How we calculate” note that writes the formula out in full, so you can check it with a pen or in a spreadsheet. We use simple payback (cost ÷ yearly saving) rather than discounted cash flow. It’s easier to follow and good enough to compare options, but it doesn’t account for interest, inflation or future price changes.
A few ground rules:
- No invented numbers. Prices, yields and efficiencies come from named public sources with a date. If a source changes, we update the data file and the date.
- Estimates, not advice. The results help you compare options and ask installers better questions. They aren’t a quote or financial advice.
- Nothing is stored. The calculators run in your browser. They don’t use cookies and don’t send what you type anywhere.
- Commission links are labeled. Under some results you’ll see links to product categories. If you buy through them we may earn a commission. That never changes the maths.
Which one should I start with?
If you’re thinking about a big purchase, start with the calculator for that product and then run “Is switching worth it?” with your own quote. If you just want to know where your money goes, the appliance calculator and a plug-in energy meter are the cheapest place to begin.
For the background behind the numbers, our guides go deeper: heat pump running costs vs gas, whether solar is still worth it without the tax credit and how long a power station will run a fridge.
FAQ
Are the calculators free?
Yes. There’s no sign-up and nothing to download. They run in your browser.
Why does a field say there’s no verified default?
Because we couldn’t find a public figure we were confident in for that country, such as solar export rates, which differ by supplier. Enter the number from your bill or quote and the result appears.
How often are the defaults updated?
We check them at least every quarter, and when a regulator publishes new prices (for example each Ofgem price cap period). The “as of” date under each calculator shows when a figure applies.
Can I use my own currency?
Yes. Choose “Other / custom”, enter your currency symbol and type in your own prices.