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Phone Charging Cost Calculator

Enter your battery and electricity details to estimate charging cost.

How it is calculated

The battery's stored energy is Wh = mAh × V / 1000, using the capacity in milliamp-hours and the nominal voltage in volts. Dividing by 1000 gives kilowatt-hours, kWh = Wh / 1000. The cost of one charge is kWh × rate, where the rate is your price per kWh in dollars, and the yearly cost is kWh × charges per day × 365 × rate. The calculation counts only the energy the battery holds. It does not add charger losses, so the real draw from the wall is somewhat higher, and it does not include standby use of the plugged-in charger. Capacity, voltage and charges per day must be above zero; the rate may be zero but not negative.

Worked example

A phone with a 4,500 mAh battery at a nominal 3.85 V, charged once a day, with electricity at 0.15 per kWh. Stored energy: 4,500 × 3.85 / 1000 = 17.33 Wh. In kilowatt-hours that is 0.017325. One charge costs 0.017325 × 0.15 = 0.0026, shown as $0.0026. Over a year: 0.017325 × 1 × 365 × 0.15 = 0.95, so the yearly cost is $0.95. At one and a half charges a day the figure rises to $1.42.

Try this example →

Common mistakes

  • Entering the electricity rate per MWh, per cent or per kWh in another currency without converting. The rate must be the price of one kWh in dollars, so 15 cents is 0.15, not 15.
  • Using the charger's rated power (for example 25 W) instead of the battery capacity. This tool works from mAh and volts, not from the charger.
  • Leaving the voltage at 5 V because that is the USB figure. Use the battery's nominal voltage, usually printed next to the capacity and typically near 3.7 to 3.9 V, otherwise the energy comes out about a third too high.
  • Expecting charging losses to be included. They are not, so the real cost is a little higher than the result.
  • Entering the daily charge as the percentage of battery used. If you recharge from 40 to 100 percent, that is 0.6 of a charge a day, not 1.

About this calculator

The energy a phone battery actually stores is its capacity in milliamp-hours converted to watt-hours using its nominal voltage: Energy (Wh) = (Capacity in mAh / 1000) × Voltage (V). This calculator does not add charging losses: chargers typically run somewhere around 80–90% efficient, so the energy drawn from the wall is somewhat higher, and you can allow for that by dividing the result by your charger's efficiency. Multiplying the per-charge energy by how many times you charge per day and by your electricity rate gives the running cost.

Because phone batteries are small — typically in the range of 10–20 Wh — the actual electricity cost of charging one, even daily over a full year, is usually just a small fraction of a typical electricity bill, which is why this kind of calculation is mostly useful as a curiosity or a way to compare charging habits and rates rather than a meaningful budgeting line item. Battery capacity, voltage, charges per day and your electricity price are combined into a cost per charge and a cost per year.

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Comments (1)

  • Editorial team

    The result assumes a full battery's worth of energy every time, and the charger and cable lose some on the way, so your meter will read a little higher. If you usually top up from 40 to 100 percent, enter 0.6 charges per day instead of 1; that case comes to about 0.63 dollars a year at 0.15 per kWh. How often do you really charge from empty?

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