Updated : Reworked the calculation to include electricity measured at the wall and clearly labelled example rates.
The cost to charge an iPhone is usually a small fraction of your electricity bill. For example, if a full charge uses 20 watt-hours at the wall and electricity costs $0.20 per kWh, it costs $0.004, or 0.4 US cents. One such charge every day would cost about $1.46 a year. These are example inputs, not a measured figure for every iPhone.
How to calculate the cost of a full iPhone charge
Use this formula:
Cost per charge = electricity used in Wh ÷ 1,000 × your price per kWh.
For the example above: 20 ÷ 1,000 × $0.20 = $0.004. The US Energy Information Administration’s units guide explains watts, watt-hours and kilowatt-hours.
| Example electricity price | Cost of a 20 Wh charge | 365 full charges |
|---|---|---|
| $0.15 per kWh | $0.003, or 0.3 cents | $1.10 |
| $0.20 per kWh | $0.004, or 0.4 cents | $1.46 |
| $0.40 per kWh | $0.008, or 0.8 cents | $2.92 |
Use your own bill rather than a national average. The formula works in pounds, euros or another currency without a currency conversion. For example, 20 Wh at £0.25 per kWh costs £0.005 per charge, or about £1.83 for 365 charges. Standing charges are not included because they are not caused by charging the phone.
How many kWh does an iPhone use to charge?
Twenty watt-hours is 0.020 kWh. Your actual figure depends on the model, starting battery level, battery wear, charger and what the phone is doing. An iPhone 15 Pro Max, iPhone 16e or iPhone 17 will not all use the same amount.
Battery capacity alone understates wall electricity use: some energy is lost as heat in the charger, cable and charging process. Wireless charging can add different losses. For a useful personal figure, use a suitable plug-in energy meter and measure several charges under similar conditions. Very small readings may be below a cheap meter’s useful resolution.
Does a 20 W charger use 20 W for three hours?
No. The number on the charger is its available output, not a constant draw. The phone changes the charging rate and slows down as the battery fills. Multiplying the maximum charger power by the time it stays plugged in can greatly overstate the cost.
Energy used per hour while using the phone is a different question from energy needed for a full charge. Gaming, screen brightness, signal strength and background apps all change that hourly figure.
What changes the yearly cost?
- How much you refill: topping up from 60% is different from charging an almost empty battery.
- How often you charge: two large refills a day cost more than one.
- Phone use during charging: a bright screen or a game adds energy beyond refilling the battery.
- Your tariff: use the unit rate that applies when you charge.
For charging habits, follow Apple’s battery guidance. If you are trying to put an older iPhone back into daily use, check whether its SIM and mobile network still work as well as its battery.