Fixed and variable electricity charges: read your bill correctly
Dividing your bill by kWh gives an average paid price, but that is not always the value of saving one more kWh. Separate charges tied to usage from charges that remain when usage falls.
By HomeCost Radar · Reviewed 2026-09-27 · Editorial policy
A simple bill before and after saving 100 kWh
Assume a $20 fixed monthly charge and a flat variable rate of $0.18/kWh, with no taxes, credits, tiers or minimum charge. These are hypothetical figures, not a utility quote.
| Case | Bill arithmetic | Total and average price |
|---|---|---|
| 500 kWh | $20 + 500 × $0.18 | $110; $0.22/kWh |
| 400 kWh | $20 + 400 × $0.18 | $92; $0.23/kWh |
| Savings | 100 × $0.18 | $18; fixed charge stays $20 |
What the example shows: The total bill falls by $18 even though the average price per kWh rises from $0.22 to $0.23. Using the original $0.22 average to price 100 kWh of savings would overstate savings by $4.
Read units beside each line item
Mark whether each charge is dollars per month, dollars per billing day, cents per kWh or another unit. A daily connection charge can vary with the number of billing days while remaining independent of energy consumption.
Names alone can be confusing. Read the utility explanation rather than deciding that every line containing the word fixed must be a flat monthly fee. SCE distinguishes its Base Services Charge from other named charges; that example does not establish the structure of every utility bill.
Separate supply, delivery and adjustments
Some bills list generation and delivery separately, with each containing usage-related components. Add the applicable variable components when estimating a small reduction in kWh, but do not add an aggregate price that already includes those same charges.
Apply taxes, credits and adjustments according to the tariff. The worked example omits them so the distinction is visible. It should not be used to contest a real bill without reconciling those additional lines.
Use average and marginal prices for different jobs
Average paid cost is useful for summarizing the total bill. The marginal price is more useful for estimating the financial effect of a small change in electricity use, provided the change stays in the same tier or time period.
For time-of-use or tiered billing, calculate the charges avoided in the affected periods or blocks. If a minimum bill applies, a usage reduction may produce less immediate bill savings than the simple variable-rate estimate.
Frequently asked questions
Why is my effective price higher in a low-use month?
Does the state-average rate include my exact fees?
Sources and assumptions
The worked examples are HomeCost Radar calculations from the stated inputs. Sources below support the concepts identified beside each link; they do not certify our assumed wattages or product savings.
- SCE: Base Services Charge — A utility example distinguishing usage charges and charges based on billing days.