Compare the electricity use and variable running cost of two appliances or usage patterns. Enter each option’s power and active hours, then choose a shared number of days and electricity rate. Add an optional extra upfront cost for Option B to explore simple payback.
Compare before you buy
Which option costs less to run?
Compare two power and usage scenarios at the same electricity rate. Use appliances that deliver comparable comfort, capacity, or output.
Make a useful comparison
Compare appliances that provide a similar service: equivalent lighting, cooling, capacity, or another outcome that matters to you. A lower power rating alone does not establish equal performance. Different operating hours can reverse which option costs less to run.
For an appliance that cycles or changes power, use average measured power across the entered hours, or the hours it actively draws the stated power. This is a scenario estimate rather than a measurement, tariff quotation, or complete ownership-cost assessment.
Understand simple payback
Enter only B’s extra upfront cost relative to A, using the same currency as the rate. If B has lower running costs, simple payback divides that premium by the daily electricity savings. The result is days at the entered daily schedules, not a guaranteed calendar date. It assumes those schedules and prices continue.
Equal or higher running costs do not recover a purchase premium through electricity savings. Maintenance, financing, installation costs not included in your premium, replacement cycles, service quality, and remaining appliance life can change the decision. A zero-day comparison does not establish a payback period.
Want to estimate just one appliance? Use the Electricity Cost Calculator.
Purpose
Compare two appliance power/usage scenarios at one shared flat tariff and period. Estimate running-cost differences and optional simple payback for B’s extra upfront cost. General principles; no regional tariff data is used.
Inputs
Each option: nonnegative power in W/kW and active hours per day from 0 to 24.
Shared days: a whole number, zero or greater.
Shared variable electricity rate: nonnegative currency/kWh or cents/pence per kWh.
Optional extra upfront cost for B: nonnegative amount in the selected major currency; blank omits payback.
Use the same currency for the rate and extra cost. Extremely large input combinations are rejected.
Units
W, kW, active hours/day, days, kWh, currency/kWh or cents/pence per kWh. USD, CAD, AUD, EUR, and GBP are labels only; no exchange conversion. Switching W/kW or rate units converts the entered number.
Currency
USD
Formula / model
For each option: daily kWh = power (W) / 1,000 × active hours/day.
Period kWh = daily kWh × comparison days.
Usage cost = period kWh × rate in major currency/kWh.
B’s running-cost savings = A’s cost − B’s cost.
B’s net difference after the entered premium = running-cost savings − B’s extra upfront cost. Positive means B is cheaper on that limited comparison.
Simple payback (days at the entered schedules) = B’s extra upfront cost / daily electricity savings, only when a premium is supplied, comparison days exceed zero, and B has positive daily savings. A zero premium has no extra cost to recover.
Currency cents/pence are divided by 100; kW input requires no W-to-kW conversion. Calculations use unrounded values.Model version
appliance-comparison-v1.0.0 / shared-electricity-model-v1.1.0
Assumptions & limitations
Each entered power applies during that option’s active hours, with the same daily schedule repeated for all comparison days. One shared flat variable rate applies. Comparable service is the user’s assumption, not established by wattage.
Fixed charges, taxes, demand charges, tiers, time-of-use prices, maintenance, financing, and replacement costs are excluded. Include any extra installation cost in B’s upfront premium if relevant. The premium is a relative extra cost, not both appliances’ full prices.
Simple payback assumes unchanged use and rates beyond the selected period and must be considered against useful appliance life. It is not guaranteed savings or a calendar recovery date. Equal/higher running costs or a zero-day comparison do not produce positive payback.
Defaults are illustrative scenarios, not measured appliance data or current market prices. Currency choices change labels only. Small positive currency amounts below 0.01 display as less than 0.01. Inputs are calculated in the browser without being sent or stored by this tool.
Worked example
Illustrative scenario: A = 100 W, B = 60 W, both 5 active hours/day for 30 days, rate USD 0.20/kWh.
A: 0.1 × 5 × 30 = 15 kWh; cost USD 3.00.
B: 0.06 × 5 × 30 = 9 kWh; cost USD 1.80.
B’s running-cost savings = USD 1.20 (40% of A’s usage cost), or USD 0.04 per day.
Optional illustrative premium for B: USD 12. Simple payback = 12 / 0.04 = 300 days at these daily schedules. After the first 30 days, B is still USD 10.80 more expensive when that premium is included. This example assumes equivalent service and excludes other ownership costs.
Sources
Virginia Cooperative Extension — ENERGY SERIES: Estimating Appliance and Home Electronic Energy Use, publication 2901-9014, February 26, 2020. Supports the watts-to-kWh and energy-cost method; historical appliance wattages and tariffs are not defaults. The comparison and simple-payback arithmetic are the explicitly documented model above. https://www.pubs.ext.vt.edu/2901/2901-9014/2901-9014.html
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