Electricity Calculator

What this calculator does differently

Most cost tools run the other way: they take a price per kilowatt hour you type in and multiply it by an appliance's watts and hours. That only works if you already know your price, and the number people usually type is whatever a utility commercial or a website told them, which is often a national average that has nothing to do with their street.

This page runs in reverse. You take one real bill, read off the total dollars and the kilowatt hours used, and divide. The result is your effective rate: what every kilowatt hour cost you that month once supply charges, delivery charges, fixed fees and taxes are all folded in. On the sample bill below that comes to 18.25 cents per kWh, well above the 16.48 cent national average the EIA reported for 2024, because this particular home uses fewer kilowatt hours than average and still pays the same fixed fees.

Once the effective rate is on the table, the appliance question becomes a straight multiplication. A 1,500 watt space heater run 5 hours a day burns 7.5 kWh daily, which at 18.25 cents is $1.37 a day, $41.06 a month, and $499.51 over a year of daily use. Those are the numbers worth knowing before winter.

The two numbers to pull off your bill

Open a recent bill and find two figures. The first is the total amount due in dollars, including every surcharge and tax, because that is what left your bank account. The second is the kilowatt hours used in the billing period, usually printed as a large number next to the meter reading dates. Both must come from the same bill, since a rate computed from a July total over June usage is a made-up number.

Beware two common traps. Billing periods rarely match calendar months: 28 to 35 days is normal, so a per-day comparison is safer than a per-month one. And estimated readings produce a bill that does not match real usage; if the bill says estimated rather than actual, wait for the next true-up. The EIA explains how it computes its own averages by dividing residential revenue by residential sales, which is exactly the arithmetic you are doing on your own bill at household scale.

If your utility shows a daily usage graph in its app, you can sanity-check the kWh figure before dividing. A home averaging 30 kWh a day should show roughly 900 on a monthly bill, and the 2024 national average was 863 kWh per month per residential customer.

Worked example: a $168.42 bill for 923 kWh

Here is a composite bill built to look like a typical deregulated-market statement. The home used 923 kWh and was billed $168.42. The statement lists three pieces: a supply charge of $61.20 for the electricity itself, a delivery charge of $95.22 for the wires and meter, and a fixed customer charge of $12.00.

Divide the total by usage: 168.42 divided by 923 equals $0.1825 per kWh, or 18.25 cents. The variable rate, with the fixed charge taken out, is 156.42 divided by 923, which is 16.95 cents. The fixed charge alone contributes 1.30 cents to every kWh at 923 kWh; if the same home had used only 400 kWh, that same $12 would have added 3.0 cents per kWh. Low-usage homes pay above-average effective rates for exactly this reason.

Why the average price is not the price of the next kWh

The effective rate is an average, and averages are the wrong price for a new decision. Utilities on tiered or inverted-block plans charge one price for the first block of kilowatt hours and a higher price for every block after that. Taxes and riders can be percentage-based too, which pushes marginal cost up further.

The household average is 14.75 cents, but the home is sitting in the second block, so the next kilowatt hour costs 18.0 cents. A 225 kWh heater added this month is billed entirely at 18.0 cents: $40.50, not the $33.19 that the average suggests. That 22 percent gap is the difference between the average and the marginal price, and it is why the calculator has an optional marginal field.

Flat-rate plans do not have this problem, and time-of-use plans replace it with a different one: the marginal price depends on the hour. If your plan charges 12 cents overnight and 28 cents from 4 p.m. to 9 p.m., run the heater at midnight and the effective marginal rate halves.

Supply, delivery, fixed fees and taxes

In most of the United States a bill is a stack of charges rather than one rate. Supply is the energy itself: in regulated states the utility generates or buys it, and in the roughly half of states with retail choice you may buy it from a marketer while the utility still delivers it. Delivery covers the local wires, substations, meters, storm costs and tree trimming. Then come fixed customer charges, riders that recover specific programs, and state and local taxes.

Each piece behaves differently as usage changes. Supply scales one-for-one with kWh. Most delivery charges scale too, though some include demand components for larger homes. Fixed charges do not scale at all, which is why they are the loudest argument for keeping your effective rate current: the same $12 charge is 4.0 cents per kWh at 300 kWh and 1.3 cents at 900 kWh. Percentage taxes ride on top of everything, so a 5 percent tax turns a 16-cent rate into 16.8 cents without appearing as a line you would notice.

When you compare the effective rate across months, remember seasonal rates exist: many utilities charge more per kWh in summer or winter peaks, so January and July numbers can differ for reasons that have nothing to do with efficiency.

Pricing an appliance at your own rate

The appliance side of the calculator is one multiplication wrapped in a unit conversion. Watts times hours gives watt-hours; dividing by 1,000 gives kilowatt hours. A 1,500 watt heater on 5 hours a day uses 7.5 kWh daily, 225 a month, and 2,737.5 a year. Multiply by the rate to get dollars.

The spread between the first and last row is what it means to use your own bill instead of a national figure: $48.37 a year for one heater, and more if you run several loads. Each additional cent per kWh is worth roughly $27 a year on this one appliance, because 2,737.5 kWh at one cent is $27.38.

The same math works in reverse for comparing products. The yellow EnergyGuide label on a new appliance estimates annual operating cost using a national average price, and the FTC's EnergyGuide page is explicit that your own cost depends on your local price, so reprice the label's kWh at your effective rate before deciding.

Where your rate sits against the national numbers

The EIA publishes the definitive figures. The national residential average was 16.48 cents per kWh in 2024, up from 16.00 in 2023, and a preliminary 17.30 cents for 2025. Those averages hide enormous state spread, because fuel mix, regulation and grid investment differ.

Two lessons fall out of that table. First, bills and rates are different things: Louisiana's residents pay a low rate but use a lot of air conditioning, so their bill lands near the national average. Second, high-rate states make efficiency worth more. At New England's 27.68 cents, the sample heater costs $757.74 a year, over half again the national-average figure, so a $60 efficient model pays for itself in months.

Your own effective rate is the only one that belongs in your decisions, but the EIA's state table is a fair way to check whether a quoted rate from a marketer is a deal or a dud.

The limits, and what to do about them

An effective rate from one bill is a snapshot. It moves with seasonal pricing, with tier position, and with any mid-year rate case your regulator approved. Recompute it whenever a bill looks different, and average two or three bills for a planning number. The calculator wants one month's numbers at a time, so enter a typical month rather than a record.

A few situations need more than division. Time-of-use plans split the day into priced windows, so compute an effective rate per window if your appliance runs mostly in one of them. Demand charges, rare for homes, price your highest 15-minute draw rather than your total. Budget billing smooths twelve months into equal payments, which makes the bill total useless for a single month; divide the annual total by the annual kWh instead, which is the same arithmetic over a longer window.

None of this changes the core move: read your own bill, divide dollars by kWh, and distrust any rate you did not compute that way. Every calculation here runs in your browser, and nothing you type is uploaded or stored. For the underlying figures, see the EIA Electric Power Monthly price table, the EIA state-by-state bill summary, and the FTC's EnergyGuide label guide.