How to calculate your electricity bill from a meter reading
If you want to challenge a bill calmly, learn the manual method once. The basic logic is simple: work out the kWh used, multiply by the unit rate, add standing charge for the billed days, then check whether anything else on the statement is an account adjustment rather than actual energy use.
The simple version
- Take the end reading and subtract the start reading.
- That gives you the usage figure the bill is trying to charge for.
- Multiply the usage by the unit rate in p/kWh and divide by 100 to get pounds.
- Multiply standing charge in p/day by billed days and divide by 100.
- Add the two subtotals together and then inspect any other lines separately.
If the bill uses multiple rates or multiple registers, split the calculation by each rate block rather than forcing everything into one number.
Related guides
What people often forget
- The bill may cover more or fewer days than the previous one.
- There may be two unit rates in one statement.
- Monthly payment changes are not the same as billed usage cost.
- Past credit, debt or refunds are separate from current energy consumption.
Official and reference sources
Frequently asked questions
Can I calculate the whole bill with one formula?
Only for a simple single-rate bill. More complex statements need separate rate blocks or register splits.
What if the bill still differs from my calculation?
Check whether the reading used was actual, whether there are multiple rates and whether the bill includes account adjustments.
Is this enough to prove the supplier is wrong?
It gives you a strong first-pass check, but you still need the reading evidence and the full statement details.
The formula, and the four things people get wrong
cost = ( units × unit rate ÷ 100 ) + ( days × standing charge ÷ 100 )
| Mistake | What happens | Fix |
|---|---|---|
| Forgetting the standing charge | Your figure is £26 a month under on dual fuel. | Always add days × p/day. |
| Using the headline cap figure as a rate | £1,862 is an older-usage annual illustration at July–September 2026 rates, not a unit rate or the revised Ofgem headline. Nothing works if you multiply by it. | Use p/kWh from your bill. |
| Counting days wrong | Off by a few pounds, and it hides genuine double-billed days. | Use the supplier’s billed days and check that consecutive periods do not overlap. |
| VAT confusion | Out by exactly 5%. | Ofgem's published cap rates include VAT. Some bills quote rates excluding it and add 5% at the end. Check which yours does. |
Gas has one extra step
Gas meters measure volume, not energy. If your meter reads in cubic metres, the bill converts it:
kWh = m³ × 1.02264 × calorific value ÷ 3.6
The calorific value is printed on your bill and is typically around 39–40. The volume correction factor 1.02264 is standard. An imperial meter reading in hundreds of cubic feet is multiplied by 2.83 first to get cubic metres. In practice: use the kWh figure the bill has already calculated, and only do this arithmetic if you are checking whether the conversion itself is right.
Step by step, with a real bill in front of you
Find the detailed charges
Not the summary page. Look for a table with Units, Rate and Amount columns — usually page two.
Note the four numbers
Opening reading, closing reading, unit rate in p/kWh, standing charge in p/day. Plus the period dates.
Do the arithmetic
Units × rate ÷ 100, plus days × standing charge ÷ 100.
| On the bill it says | What it means |
|---|---|
| Previous reading / Present reading | Opening and closing. Marked A, E, C or S for the reading type. |
| Units used / Consumption | The difference between them, in kWh. |
| Unit rate / Price per kWh | In pence. Check whether it says including or excluding VAT. |
| Standing charge | Pence per day, plus the number of days. |
| Two rate lines for one fuel | The cap changed mid-period. The days should split between them and add up to the total period. |
Use the bill from meter reading calculator to skip the mental arithmetic, or the annual estimator for a whole-year figure.
Annual energy bill estimator
Enter your yearly usage in kWh — it is on your annual statement, or add up the units from four quarterly bills. Pick your region and the current cap rates fill in automatically. Override them with the rates on your own bill if you are on a fixed tariff.
Standing charges account for £314.74 of this — 17% of the total before you use anything.
Rates shown default to the Ofgem cap for 1 July to 30 September 2026, direct debit, including VAT. This is a sense-check, not a quote, and it does not model time-of-use tariffs.
Frequently asked questions
How do I calculate my electricity bill?
Units used times the unit rate in pence, divided by 100, plus days billed times the standing charge in pence, divided by 100. Units used is the closing reading minus the opening reading.
Where do I find the unit rate on my bill?
In the detailed charges section rather than the summary, usually on page two, in a table with Units, Rate and Amount columns. If the bill covers a period where the cap changed you will see two rate lines.
Does the calculation include VAT?
Domestic energy carries 5% VAT. Ofgem's published cap rates include it. Some bills quote rates excluding VAT and add it at the end — check which yours does, because getting it wrong puts your answer out by exactly 5%.