Advanced options
What The Phone Charging Cost Calculator Works Out
- Per charge: the battery's watt-hours plus 30% for charging losses (heat in the charger and battery), divided by 1,000 and multiplied by your unit rate, which defaults to the current Ofgem price cap unit rate. A 13Wh smartphone battery costs under half a penny to fill from empty.
- Per year: the per-charge cost multiplied by your daily charges and 365. A nightly-charge year lands near GBP 1.50, less than a single coffee; even a laptop's nightly top-up stays inside a fiver.
- Perspective: the year's kilowatt-hours expressed as kettle boils at about 0.11 kWh a boil. One kettle boil equals roughly six phone charges and one tumble dryer cycle equals a year and a half of them.
- Custom battery capacity (advanced): enter the watt-hour figure printed on the battery or in the spec sheet. If you only have milliamp-hours, multiply by the voltage (usually 3.7V to 3.85V) and divide by 1,000: a 5,000mAh phone is about 19Wh.
- Charging losses (advanced): the default 30% covers the warm charger and warmer battery. Fast charging and wireless pads run less efficiently, often 40% to 50% losses, without moving the total anywhere that matters.
- Number of devices (advanced): multiplies the totals for a household's phones, tablets and laptops charged on the same pattern.
- Idle charger per year (advanced): the cost of a charger left plugged in with nothing attached. Modern USB adapters idle at a few milliwatts so the default is zero; an old adapter drawing 0.5W all year costs about GBP 1.20, and is worth retiring on safety grounds alone.
- Charging overnight off-peak (advanced): the same kilowatt-hours priced at an Economy 7 or EV tariff night rate, typically 7p to 16p, and the saving against your day rate. It is pennies, which is the point.
- Over the device's life (advanced): charging plus idle-charger cost for the years you keep the handset. The greenest phone decision by a wide margin is keeping it longer rather than charging it more carefully. Charging habits matter for battery lifespan rather than the bill: lithium cells age fastest held at 100% and hot, which is why optimised charging pauses at 80% overnight.