Phone & Laptop Charging Cost Calculator
Find out how little it really costs to charge your phone, tablet or laptop — per charge and per year — from battery size and your electricity rate.
How it works
Energy per charge (Wh) = mAh × volts ÷ 1000 ÷ efficiency · Cost = energy(kWh) × price · Yearly = cost per charge × charges/day × 365
A battery’s energy in watt-hours is its charge capacity in amp-hours times its voltage, so a mAh rating alone is only half the picture. Because chargers lose some energy as heat, the wall draws more than the battery stores — dividing by an efficiency near 0.8 captures that. The result surprises most people: even daily charging costs a tiny fraction of a home electric bill, because phones and laptops hold only a few dozen watt-hours.
Worked example
A 4,000 mAh phone at 3.85 V stores 4,000 × 3.85 ÷ 1000 = 15.4 Wh. At 80% efficiency the wall supplies 19.25 Wh, so at $0.17/kWh one charge costs about $0.0033. Charging once daily is roughly $1.19 a year.
Frequently asked questions
Why divide by efficiency instead of multiply?
The battery ends up holding its rated watt-hours, but the wall outlet must supply more because the charger and battery waste some as heat. Dividing stored energy by an efficiency below 1 gives the larger amount you actually pay for.
Does leaving the charger plugged in add cost?
A modern charger left plugged in with nothing attached draws a fraction of a watt — pennies a year. The vampire-power calculator handles that idle draw if you want to total it across many devices.
What voltage should I use for a laptop?
Use the battery’s nominal voltage, not the charger’s output. Many laptop packs are around 11.1 V; the value is usually printed on the battery or in its specs. Capacity in Wh, if listed, can be entered as mAh × V already combined.
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This calculator is for educational purposes. Double-check important results before acting on them.