Frequently Asked Questions

Enter the older reading as the previous reading and the newer one as the current reading. The calculator subtracts the older number from the newer one to find how many units you used.

It is the number of days between the two readings. If you took readings on 1 June and 1 July, the billing period is 30 days. A date calculator can help when the period crosses several months.

Look at a recent bill, tariff information label or your supplier’s app. The unit rate is normally shown in pence per kWh. The standing charge is shown in pence per day. Use the rates that applied between your two readings.

If you have a meter reading from the day the price changed, split the period there and run the calculator once for each set of rates. Without that reading, your supplier’s bill should give the more accurate breakdown.

A kilowatt hour (kWh) is the unit used to measure electricity. For example, a 1,000-watt appliance running for one hour uses 1 kWh. Your meter keeps a running total of these units.

Read from left to right. Ignore numbers after the decimal point and any final red digit. Dial meters need a slightly different method; our meter guide shows each type.

Usually not, because a working smart meter sends readings automatically. You may still want a manual reading to check a bill or use this calculator. Read the fixed meter, not the small in-home display.

First check that both readings came from the same meter and register. A meter may occasionally roll back to zero after reaching its maximum. If neither explains it, take a photo and contact your supplier rather than guessing.

These meters have two readings and two unit rates. Run the calculator separately for each register using the matching rate, then add the results. Enter the standing charge on the first calculation and use 0 for the second so it is only counted once.

It is a fixed daily charge from your supplier. You pay it for every day your property is connected, even on days when you use no electricity.

Your bill may cover different dates or use an estimated reading. It may also include a price change, account credit, debt repayment, discounts, more than one meter rate or slightly different rounding. Compare the readings and dates first.

No. It simply assumes you keep using electricity at the same daily rate for a full year. Real use usually changes with the weather, daylight hours, holidays and changes at home.

No. Where it applies, the cap limits tariff rates rather than the final amount you can be charged. Your total still rises or falls with the electricity you use.

Yes, if you know your readings, unit rate and standing charge. It will estimate the energy cost, but it will not include debt recovery or other adjustments taken when you top up.

No. The calculation happens in your browser. The latest result is kept temporarily in session storage so the results page still works after a refresh, and it is cleared when the browser session ends or you start again.

No. Gas meters measure volume, which must be converted to kWh before the bill is calculated. Use the separate Gas Bill Calculator instead.

Start with appliances that heat rooms, water, food or clothes, then check things that run for long periods. Our guide to reducing electricity bills has a practical checklist.