All worked examples below use explicitly chosen inputs. They are not measured household averages, utility quotes, or guaranteed savings.
Collect the same four values from each bill
Record billing days, electricity used in kWh, the combined applicable per-kWh rate, and remaining charges. Keep electricity separate from gas, water, past-due balances, and one-time adjustments.
If you divide the entire bill by kWh and also enter fixed charges, you count those fees twice. Use the variable supply and delivery components when the bill separates them.
- Check whether meter readings are actual or estimated.
- Compare the same service address and meter.
- Use the utility’s interval data if the plan has several time-of-use prices.
Normalize the number of billing days
An example old bill has 600 kWh over 30 days: 20 kWh/day. A new bill has 770 kWh over 35 days: 22 kWh/day. Total kWh rose 28.3%, but daily use rose 10%. The five extra days explain part of the difference.
A $51.40 increase, explained step by step
Assume the old rate is 20¢/kWh with $10 of other charges; the new rate is 22¢ with $12 of other charges. The old modeled bill is $130; the new one is $181.40.
We change days first, daily usage second, price third, and other charges last. Another ordering can allocate interactions differently, so treat the components as a transparent decomposition, not independent causal measurements.
| Contribution | Calculation | Change |
|---|---|---|
| Billing days | 5 × 20 kWh/day × $0.20 | +$20.00 |
| Daily use | 2 kWh/day × 35 × $0.20 | +$14.00 |
| Variable price | 770 × ($0.22 − $0.20) | +$15.40 |
| Other charges | $12 − $10 | +$2.00 |
Investigate only after separating the numbers
If daily kWh rose, compare schedules, occupancy, seasonal heating or cooling, and newly added equipment. The arithmetic cannot establish which of those changed. If kWh is similar but the price rose, check the tariff and rate notices. EIA describes several supply and demand factors behind electricity prices.
Use your utility’s billing support for unexplained readings or adjustments. The analyzer does not validate a meter, diagnose a wiring fault, or reconstruct a complex tariff.
Sources & calculation notes
References checked 2026-10-09. Example arithmetic is calculated by HomeWattCheck. Article review dates are separate from the EIA data period displayed in our calculators.
Each calculator states its scope beside the result. Appliance tools estimate electricity at one rate; the time-of-use comparator includes two price periods and entered fixed fees. Complex tariffs may need additional calculations. State averages describe reported residential revenue per kWh, not your utility’s offer. See our data sources and methodology or state rate comparison.