Kilowatt-Hour Cost Calculator: What's It Actually Costing You?
Every kilowatt-hour used has a price tag attached to it, whether or not anyone checks the number. A 3.2 kW central air conditioner running seven hours a day at a flat rate of $0.15 per kWh adds up to $3.36 that day, $100.80 that month, and $1,226.40 across a year: figures a wattage rating by itself never shows, because a rating is a rate of use, not a bill.
- Daily
- $3.36
- Monthly
- $100.80
- Annual
- $1,226.40
What this page is actually solving for
This page has one job: turning a load and a run-time into money. It assumes the load in kilowatts is already known and the run-time is already known, and it converts those two inputs, plus a rate, straight into a dollar figure. Working out how many kilowatts a specific appliance draws in the first place (a refrigerator, a space heater, a window unit) is a separate question, covered on the home energy use page, which lists typical wattages for common household loads. And working out the raw kilowatt-hour figure from a known load and a known number of hours, without the dollar step, is covered on the kilowatts to kilowatt-hours page. This page picks up right where that one leaves off, at the point where a kWh number needs to become a cost.
That distinction matters because the three questions get confused constantly. "How much power does it use," "how much energy does it use," and "how much does it cost" all sound similar, but they are three different units (kW, kWh, and dollars), and only the last one is what shows up on a bill.
The "hours/day" input deserves a second look before it goes into the calculator, because it means actual run-time, not hours plugged in. A central air conditioner isn't running its compressor for every one of the hours it's powered on: a thermostat cycles it on and off to hold a temperature, and 7 hours/day in the worked example is a duty-cycle average across a full day, not a continuous 7-hour stretch. The same is true of a refrigerator's compressor, a water heater's element, or anything else controlled by a thermostat or a cycle timer. Reading "always on" as "24 hours/day" for a cycling load is a common way to overstate a cost estimate by a wide margin.
How the cost formula is built
Energy is power sustained over time: multiplying a load in kilowatts by the number of hours it runs gives kilowatt-hours, the unit a utility actually bills. Multiplying that kWh figure by the price per kWh gives the cost. Extending a single day's cost out to a month or a year is just repeated multiplication, using 30 days and 365 days as round approximations of a billing cycle and a calendar year.
Every input in that formula is something a person controls or can look up: the load from a nameplate, the hours from an honest estimate of actual run-time, and the rate from a utility bill, which is what makes the output more useful than a flat "energy use is expensive" statement. It turns a vague worry into a specific number.
It's worth noticing what the formula does not need: voltage, current, or power factor never enter into it. Those matter for sizing a circuit or picking a breaker, which is a separate question handled on pages like the kilowatts to amps page, but the cost math only cares about the load's real power in kilowatts and how long it runs. A 3.2 kW load costs the same whether it draws that power at 120 V or 240 V, single-phase or three-phase. The meter bills for energy delivered, not for the electrical path it took to get there.
Worked example: the central air conditioner
3.2 kW central air conditioner, running 7 hours a day, at a flat rate of $0.15 per kWh.
- 1
Find the daily energy use
kWh = 3.2 × 7 = 22.4 kWh/day
- 2
Apply the rate to get daily cost
22.4 × $0.15 = $3.36/day
- 3
Scale to a month (× 30)
$3.36 × 30 = $100.80/month
- 4
Scale to a year (× 365)
$3.36 × 365 = $1,226.40/year
This uses a single flat rate for the whole year. A real bill can run higher once fixed charges, delivery fees, taxes and any time-of-use or tiered pricing are layered on. See the FAQ below for how those pieces work.
The same load, five different rates
The load and the run-time in the table below never change. It's the same 3.2 kW air conditioner running 7 hours a day, or 22.4 kWh/day, in every row. Only the $/kWh rate changes, to show how much the rate alone moves the bottom line. Real utility rates vary by region and by provider, and many plans also vary by time of day (time-of-use pricing) or by how much has already been used that month (tiered pricing). The flat rates below are illustrative reference points, not a specific utility's published schedule.
| Rate ($/kWh) | Daily cost | Monthly cost | Annual cost |
|---|---|---|---|
| $0.10 | $2.24 | $67.20 | $817.60 |
| $0.15 | $3.36 | $100.80 | $1226.40 |
| $0.20 | $4.48 | $134.40 | $1635.20 |
| $0.25 | $5.60 | $168.00 | $2044.00 |
| $0.30 | $6.72 | $201.60 | $2452.80 |
Reference figures only, computed from a fixed 3.2 kW / 7 h load, not a substitute for a real utility rate schedule.
What a flat rate leaves out
A single $/kWh rate, multiplied through, is a genuinely useful estimate, but it's still an estimate, not a bill. Real residential pricing gets more layered than one flat number in a few common ways. Time-of-use plans price the same kWh differently depending on the hour it was used, sometimes by two or three times between peak and off-peak windows. Tiered plans raise the $/kWh rate itself once a household crosses a monthly usage threshold, so the marginal cost of running one more appliance depends on how much has already been used that month. And a printed bill almost always includes charges beyond energy itself, a fixed customer fee, delivery and transmission charges, taxes and regulatory surcharges, none of which scale with kWh use the way the energy charge does.
None of that makes a flat-rate estimate wrong to use. It makes it a starting point. It's the right tool for comparing two appliances, sizing up whether a purchase is worth it, or getting a rough sense of an annual number before a bill arrives. For the finer detail on how each of those complications changes the math, see the FAQ below. And for the reverse question, sizing generation rather than estimating cost, the solar system size page works from a household's daily kWh figure toward a panel array, and the generator sizing page works from a list of appliance loads toward a backup generator's kW rating.
Working out usage before cost
Questions
Kilowatt-hour cost FAQ
What changes once a flat-rate cost estimate meets a real utility bill.
What are time-of-use (TOU) rates, and how do they change this calculation?
A time-of-use rate charges a different price per kWh depending on when the electricity is used, instead of one flat number all day. Peak afternoon and evening hours are commonly priced two to three times higher than overnight off-peak hours. This calculator (and the worked example above) uses a single flat rate, which is a simplification. Running the same 3.2 kW, 7-hour load entirely inside a peak window on a TOU plan can cost noticeably more than the flat-rate estimate suggests, while shifting it to an off-peak window can cost less. The actual bill depends on when the appliance runs, not just how long it runs.
Why is my actual electric bill higher than daily kWh times my rate?
Because the number printed as a "rate" on a bill is usually just the energy charge, and a residential bill layers several other charges on top of it. A fixed monthly customer or service charge applies whether the meter turns or not, delivery and transmission charges cover getting the power to the house, and local taxes or regulatory surcharges add a further percentage. A kWh × rate estimate like the one on this page approximates the energy portion of the bill well, but it is not the whole invoice.
How do tiered utility rates complicate a flat-rate cost estimate?
Under a tiered rate structure, the $/kWh price itself increases once monthly usage crosses a threshold, so the same appliance can cost different amounts per kWh depending on how much electricity the rest of the house has already used that month. As an illustrative example, a utility might charge $0.14/kWh for the first 800 kWh in a month and $0.20/kWh above that. A load added near the start of a billing cycle gets priced at the lower tier; the identical load added after the household has already crossed the threshold gets priced at the higher one. A single flat rate, like the one this calculator uses, can't capture that shift. It's a reasonable estimate, not a tier-aware bill simulator.
How can I use a cost estimate like this to decide whether an appliance is worth buying?
Enter the appliance's rated wattage (converted to kW) and a realistic daily run-time, then compare the resulting annual cost against the price difference between models. A small $/kWh gap compounds fast once it's multiplied by a year of use. For example, an appliance that runs one fewer hour a day than a competing model saves 1 kW-hour of runtime per kW of rating each day; at $0.15/kWh and 1 kW of rated draw, that is about $0.15/day, or roughly $54.75/year, a number worth weighing against any higher purchase price for the more efficient option.
Where do I find the $/kWh rate to enter into this calculator?
The most reliable source is a recent electric bill: divide the total dollar amount charged for energy by the total kWh used in that billing period to get a blended average rate. That blended figure already folds in any tiered pricing or time-of-use averaging that happened during the billing period, which makes it a more realistic input than a rate pulled from a generic published table. Utilities also publish their current rate schedules directly, for anyone who wants the unblended peak, off-peak, and tier breakpoints.
Does running a large appliance at night actually save money?
Only under a time-of-use rate plan: under a flat-rate plan, the clock has no effect on cost at all, because the $/kWh figure is identical no matter when the meter turns. Using the illustrative rates in the table above, the same 3.2 kW, 7-hour load costs $2.24 at a $0.10/kWh off-peak rate versus $6.72 at a $0.30/kWh peak rate, a $4.48/day difference that exists purely because of timing. Whether shifting a load overnight is worth the inconvenience depends entirely on how wide the peak-to-off-peak spread is on the specific plan in question.
Does raising an air conditioner's thermostat setting meaningfully cut the cost?
Yes, roughly in proportion to how much daily run-time it removes. A thermostat change that shortens the compressor's daily run-time has a direct, calculable effect on the cost this page computes. Take the 3.2 kW unit from the worked example above: cutting its run-time from 7 hours/day to 5 hours/day at $0.15/kWh drops the daily cost from $3.36 to $2.40, a saving of $0.96/day, about $28.80/month or $350.40/year. The unit itself did not get more efficient; it simply ran for less time.