Enter how much energy you used, in kWh.
Enter your unit rate, in pence per kWh.

What this does

Works out what your bill should be from your own figures, compares it against what you were charged, and — if the two disagree — walks through the reasons that usually explain it, most likely first.

It asks the follow-up questions only once there is a gap to explain. Before that, they would be questions about a bill with nothing wrong with it.

What it cannot tell you

Whether your supplier has billed you incorrectly. No calculator can show that, and it is worth being clear about why: the figures you enter are the ones you have, and the most common reasons they do not match a bill are an estimated meter reading, a rate that changed part-way through, or a period that is a different length than you assumed.

All three are ordinary and none is anyone’s fault. So this page tells you the entered figures do not fully explain the bill, which is what the evidence supports, and lists what to check.

Start with the reading

If the bill says “estimated” anywhere near the meter readings, stop and send an actual reading before doing anything else. The period gets rebilled against it. Until that happens nobody can tell whether the bill is wrong or the estimate is, and it costs nothing to find out.

How to read an electricity meter and how to read a gas meter.

If the figures do agree

Then the bill is right and the question changes: not “why is this wrong” but “why is my usage what it is”. That is a better problem to have, because it is one you can act on.

The most useful next step is almost always the overnight base load check — two meter readings that tell you what your home draws while nobody is using anything. After that, the appliance running cost calculator puts numbers on individual suspects.

Nothing is stored

Everything you type stays in this browser tab. No meter reading, bill total or usage figure is sent anywhere, and none is kept when you close the page.