How to Calculate an Electricity Bill from Meter Readings

Subtract the previous cumulative kWh reading from the current one to find energy used, then apply your utility's actual tariff. That calculates the starting energy quantity. It does not mean the full bill is simply units multiplied by one price.

Collect the right inputs

Use the previous and current readings for the same register, their dates, and the published tariff for your connection and billing period. Check whether readings are actual or estimated. If the meter was replaced, reset, or rolled over, the utility's adjustment must be included rather than applying a simple subtraction across unrelated readings.

Some installations have a stated billing multiplier. Use it only when the bill or provider specifies it. Homes with solar, time-of-use registers, or other special arrangements may need separate import, export, and period readings.

Calculate energy used

Energy used (kWh) = current reading − previous reading

If the readings are 4521 kWh and 4185 kWh, the difference is 336 kWh. “One unit” commonly means one kWh in electricity billing, but check the units printed on your bill.

For comparing months of different lengths, divide by billing days. To calculate the bill itself, use the utility's actual period and rules. Do not replace actual billed units with a normalized 30-day estimate.

Apply the tariff exactly as written

For a hypothetical flat energy rate of ₹6.50/kWh, 336 kWh produces ₹2184 in energy charges. With an illustrative $0.20/kWh rate, the same energy costs $67.20. Neither is a quoted local tariff.

Some tariffs use progressive slabs; others have different structures, thresholds, subsidies, or time-of-use prices. Do not assume every utility applies the highest rate only to the last units. Read the rules for your category and billing dates.

Here is a purely illustrative progressive schedule: first 100 kWh at ₹3, next 200 at ₹5.50, and any remaining units at ₹8. For 336 kWh, the arithmetic is:

100 × ₹3.00 = ₹300
200 × ₹5.50 = ₹1100
36 × ₹8.00 = ₹288
Energy charge = ₹1688

This demonstrates that particular progressive structure. It is not a rate card for India and should not be substituted for your electricity company's schedule.

Add the other bill items

Check fixed or connection charges, demand charges where applicable, fuel or power-purchase adjustments, taxes, duties, meter/service charges, arrears, credits, and subsidies. Which items exist and how they are calculated vary by provider. Export credits may use a different rate from imported energy.

A simple calculator using one entered tariff estimates energy cost only. It cannot reproduce every slab, tax, credit, or billing correction without those rules being supplied. Label a projection clearly so it is not mistaken for an official bill.

Keep pulse estimates separate

Pulses can estimate a short-period average load using watts = 3,600,000 × pulses ÷ (imp/kWh × seconds). For example, 32 intervals in 36 seconds at 3200 imp/kWh give 1000 W. That does not prove the load stays at 1000 W all month. Use cumulative kWh for the billing period where available, and ask the provider to explain a difference that remains after checking the readings and tariff.