In most cases your electricity bill will be arithmetically correct, but "correct" and "based on accurate information" are not the same thing — the calculation is only ever as good as the meter reading and the tariff details fed into it. You can verify your own bill in an evening by checking three things in turn: that the meter reading used is a real reading rather than an estimate, that the unit rate and standing charge printed on the bill match the tariff you actually agreed to, and that the sums add up when you multiply the energy used by those rates. The rest of this article explains how each of those steps works and where errors tend to creep in.
Almost every domestic electricity bill in Great Britain is built from the same handful of ingredients, and once you can name them the document stops being intimidating. The core components are:
The headline figure at the top of the bill is simply these parts added together. If you can locate each one, you can reproduce the total yourself — and any discrepancy between your reproduction and the printed figure is exactly where you should focus.
The single most common reason a bill is wrong is that it was calculated from an estimated reading rather than a real one. Suppliers estimate consumption when they have not received an actual reading, projecting your likely usage from historical patterns. Estimates are legitimate and self-correcting over time, but a poor estimate can leave you paying for energy you have not used, or building up a debt that lands as a shock later.
Look on the bill for a letter code beside each reading. Conventionally, an A denotes an actual reading taken from the meter, an E an estimate, and a C a reading you supplied as a customer. If either the opening or closing reading is estimated, walk to your meter and compare the number displayed there with the closing figure on the bill. If they differ materially, submit your own reading and ask for the bill to be recalculated. For a smart meter operating in the correct mode this problem should not arise, but smart meters can lose their communications link and quietly fall back to estimates, so the same check is worth doing.
The second layer of verification is checking that the unit rate and standing charge on the bill are the ones from your actual contract. Rates change — a fixed deal ends and you roll onto a variable tariff, a price change takes effect partway through a period, or you switch supplier — and each change is a moment where the wrong number can be applied. Compare the rates printed on the bill against your latest tariff information, contract confirmation or annual statement.
Pay particular attention to billing periods that straddle a price change, because the supplier must split the period and apply each rate to the correct number of days. If you are on an Economy 7 or other time-of-use tariff, confirm that day and night units have been recorded and priced separately rather than lumped together at a single rate. Note too that variable tariffs move in line with a regulated cap set by Ofgem; the cap limits the rates a supplier may charge, but it does not cap your total bill, which still depends entirely on how much energy you use.
With verified readings and verified rates, the final step is mechanical. Subtract the opening reading from the closing reading to get the units used, then work through the calculation:
If your total lands close to the printed figure, the bill is sound. If it does not, you have now isolated the problem to a specific number — a wrong reading, a wrong rate, a miscounted number of days, or a missing adjustment — which is far easier to raise with your supplier than a vague sense that "the bill seems high".
A bill can be internally consistent and still be wrong for reasons that sit outside the arithmetic. Transposed or swapped meter serial numbers can mean you are being billed for a neighbour's meter, so check that the serial number on the bill matches the one physically on your meter. After a supplier switch, confirm that the closing reading from your old supplier and the opening reading from your new one agree, since a mismatch here causes one company to over-bill and the other to under-bill. Finally, be alert to catch-up charges: if a long run of estimates is suddenly corrected by a real reading, a large "true-up" can appear that is genuinely owed but feels like an error — the reading history on the bill will tell you which it is.
If your checks turn up a genuine discrepancy, contact your supplier with the specific figures — the reading you have taken, the rate you expected, and the recalculation you have done. Suppliers are obliged to investigate billing queries and to correct errors. There are also rules limiting how far back a supplier can bill you for energy it previously failed to charge for, so if you are presented with a very old back-bill it is worth asking whether those protections apply. Should the supplier fail to resolve a legitimate complaint, you can escalate it to the Energy Ombudsman, whose decision the supplier is bound to honour.
Why is my bill so much higher than last time when nothing has changed? The two usual explanations are a switch from estimated to actual readings, which corrects an under-estimate in one lump, and a rise in the unit rate or standing charge. Check the reading codes and compare this period's rates with the last bill's; between them they explain the large majority of unexpected increases.
Can I be charged for electricity I never used? Not for energy that never passed through your meter — the meter reading is the physical record of consumption. You can, however, be charged on an inaccurate estimate, or on the wrong meter entirely if serial numbers are mixed up. Verifying the reading against the meter and checking the serial number rules both of these out.
How often should I submit my own meter reading? If you do not have a working smart meter sending automatic readings, submitting a reading around each billing date keeps your bills based on reality rather than estimates. Regular readings prevent both overcharging and the build-up of a surprise balance that a delayed real reading can otherwise trigger.