Electricity Cost

How Your Electricity Cost Is Calculated

Your electricity cost is your monthly usage in kilowatt-hours (kWh) multiplied by your price per kWh, plus any flat monthly service charge your utility bills regardless of usage. Enter your monthly usage and rate — both are printed on a recent utility bill — and this calculator estimates your monthly and yearly electricity cost.

Usage-based cost is the part that changes with how much electricity you actually use. The fixed service charge (sometimes called a “customer charge” or “basic service fee”) is a flat amount some utilities bill every month on top of usage, covering the cost of maintaining the connection to your home regardless of how much power you draw.

The Formula

$$\vD{\text{Energy Cost}} = \vA{\text{Monthly Usage (kWh)}} \times \vB{\text{Rate per kWh}}$$ $$\vE{\text{Total Monthly Bill}} = \vD{\text{Energy Cost}} + \vC{\text{Fixed Monthly Service Fee}}$$ $$\text{Estimated Annual Cost} = \vE{\text{Total Monthly Bill}} \times 12$$

The annual figure is a simple 12-month projection at this month’s usage and rate — it doesn’t adjust for seasonal usage swings (like summer air conditioning or winter heating) or future rate changes, unlike the Solar Savings Calculator’s multi-year projection, which does model rate inflation over time.

Worked Example

900 kWh of usage at $0.18/kWh, with a $10 flat monthly service fee:

1. Energy cost: 900 × $0.18 = $162.
2. Total monthly bill: $162 + $10 = $172.
3. Estimated annual cost: $172 × 12 = $2,064.

If you’re evaluating whether solar panels would be worth it, this monthly bill total is exactly the number the Solar Savings Calculator needs as its starting point.

Key Factors to Consider

• Seasonal usage swings mean a single month rarely represents your true annual average. Heating and cooling usage in particular can vary enormously between a mild spring month and a peak summer or winter month — using several months’ worth of bills (or a full year’s total divided by 12) gives a more representative monthly average than any single month alone.
• A time-of-use rate plan can make the same total usage cost very differently depending on when it happens. Under a time-of-use structure, running high-usage appliances during peak pricing hours costs more than running them during off-peak hours, even for identical total kWh — shifting usage timing (not just reducing it) can meaningfully affect the bill under this kind of plan.
• Rates change over time, sometimes significantly. Utility rates are periodically adjusted through regulatory filings — a rate from a bill a year or two old may no longer reflect what you’re actually being charged today, so use your most recent bill for the most accurate estimate.
• A separate delivery/transmission charge is sometimes billed apart from the energy supply charge. Some utility structures (especially in deregulated markets) separate the cost of the electricity itself from the cost of delivering it — check whether your bill’s “rate” already includes both, since combining only one would understate your true per-kWh cost.

Common Mistakes

• Using a rate from an old bill. As noted above, utility rates change periodically — a rate pulled from a bill that’s a year or more old may no longer match what you’re actually being charged, especially after a rate case or seasonal rate change.
• Forgetting to include the fixed monthly service fee. Skipping this (or leaving it at a nonzero default when your utility doesn’t actually charge one) throws off the total by a consistent amount every month — check your bill specifically for a flat charge separate from usage.
• Confusing kWh (energy) with kW (power). Usage is billed in kilowatt-hours, a measure of energy consumed over time, not kilowatts, which measures the rate of power draw at a single instant — see the Electrical Power Calculator calculator if you need the power side of this distinction.
• Assuming a single month represents your typical usage. As covered above, seasonal swings from heating and cooling can make one month’s bill a poor stand-in for your real annual average — pull a few months’ worth of bills, or a full year’s total divided by 12, for a more representative estimate.

Useful to Know

• kWh is a unit of energy (power sustained over time), not power itself — 1 kWh is the energy used by a 1,000-watt device running for one hour. See the Electrical Power Calculator calculator to convert a device’s wattage into an hourly energy draw.
• If you’re comparing this bill against a potential solar installation, this calculator’s total monthly bill figure feeds directly into the Solar Panel Savings Calculator calculator’s own starting input, so there’s no need to re-derive it there.
• Many utilities publish their current rate schedules on their own website, which is a more reliable way to check for a rate change than relying solely on a bill that might be a few months old.
• A sudden, unexplained jump in usage between otherwise similar months (independent of the season) can be an early sign of a failing appliance, a phantom load left running, or occasionally a metering error worth reporting to the utility.