Electricity calculators with the math shown

Invented numbers, run through the same formulas the calculators use. The point is the order: price first, then the cost of a habit, then whether paying for a change makes sense.

1. Price per kWh. A bill shows $250.00 of electric charges for 1,500 kWh. The all-in average is 16.67¢/kWh. Its per-kWh lines add up to $220.00, so the price of the next kWh is 14.67¢/kWh; the other $30.00 doesn't change when usage does.
2. Cost of a habit. A 1,500 W space heater running 4 hours a day for 30 days uses 180 kWh, which costs $26.40 at 14.67¢/kWh. Using the all-in average instead would overstate it.
3. Value of a change. Running it 2 hours a day instead uses 90 kWh, saving 90 kWh and $13.20 over the 30 days. No purchase needed.
4. Payback of a purchase. An upgrade expected to save 600 kWh a year is worth $88.00 a year at the same price. If it costs $300.00 after confirmed incentives, simple payback is 3.4 years.

Each step changes if one input does. A different price of the next kWh changes every later number, which is why the price per kWh calculator comes first.

Three prices can be read from the same bill, and they answer different questions. The all-in average (every electric charge divided by kWh) describes what this bill cost per kWh. The price of the next kWh (only the charges priced per kWh) is what one more or one fewer kWh is worth, so it belongs in every savings and payback calculation. Percentage-based taxes rise and fall with the bill, so real savings can be slightly higher than the price of the next kWh suggests.

Tiered rates add a third: on FPL's and JEA's current residential rates, the price of the next kWh steps up above 1,000 kWh in a billing period. Before taxes and local fees, FPL's is 12.258¢ below that line and 14.258¢ above it; JEA's is 12.790¢ and 14.680¢ on its November 2026 fuel rate. If your bill usually crosses 1,000 kWh, kWh you save come off the higher price first. Those are the values behind the FPL and JEA presets in the calculators.

1. Using the amount due. It can include a past balance, deposits, late fees, and water, sewer or gas. Use this period's electric charges.
2. Treating label watts as average watts. The label shows the maximum; anything with a thermostat or compressor cycles. Lower the share-of-time field or measure the appliance.
3. Using horsepower for a pump. Horsepower is mechanical output. The calculators need electrical input in watts.
4. Using someone else's rate. A national or statewide average can be far from your tariff, and from the price of your next kWh in particular.
5. Adding savings from several changes. Many changes overlap: a thermostat setback and a more efficient air conditioner both reduce the same cooling load. Value each one separately, and treat any total as an upper bound.

Simple payback is the net cost divided by the yearly savings. It's a quick test, and it leaves several things out on purpose, so read it alongside these questions:

• Will you keep it that long? Compare the payback period with how long you expect the equipment to last and how long you expect to stay in the home. A payback longer than either means the bill savings alone won't cover the cost.
• Were you replacing it anyway? If the old unit has failed, the cost to weigh is the difference between the efficient option and the standard one, not the full price.
• How sure is the savings figure? The payback calculator takes a low estimate and an optional high one and shows payback for both. If the answer changes from "worth it" to "not worth it" between the two, the decision rests on the estimate, and it's worth measuring before you buy.
• Does upkeep change? Some upgrades add a yearly cost, such as a subscription or extra maintenance, and some remove one. Enter it as the change in yearly upkeep, as a negative number if upkeep falls; it comes off the savings before payback is worked out.
• What about financing and price changes? Simple payback ignores interest on a loan and future changes in electricity prices. A loan lengthens the real payback; rising prices shorten it.

If yearly savings come out at zero or below, the calculator says the upgrade doesn't pay back on energy cost alone. If confirmed rebates cover the whole price, there's nothing to pay back. Both are useful answers, not errors.

• Usage jumped and you can't say why. Look at when the electricity was used before estimating anything. FPL's free Energy Manager shows when and how a home uses energy, and a JEA bill carries 13 months of usage history. JEA also offers free efficiency assessments by phone appointment.
• Explaining a change between two bills. The bill comparison splits the change into usage, price and fixed charges, and splits usage further into billing days and daily use, so the parts add up exactly to the difference.
• Something seems unsafe. Hot outlets, a burning smell or a breaker that keeps tripping are for a licensed electrician, not a cost estimate.
• Choosing a time-of-use rate. That depends on the hours your usage falls in, which a monthly bill doesn't show. See how to work out a time-of-use break-even.
• Sizing solar. The calculators don't model solar production or export credits. On a JEA bill, exported power is credited at JEA's fuel rate; see the JEA page.
• Diagnosing a whole house. Finding where heat gets in or which duct leaks takes an in-person look. Our guide to what online tools can and can't tell you explains when an in-home audit is the next step.