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Battery & power

How far will your battery go?

Estimate laptop runtime from battery capacity and average power. Then see what the same active workload could cost on your own electricity tariff.

Free to use · Calculations stay in your browser · No sign-up

Start with your battery.

Capacity & charge

Use watt-hours from the manufacturer or a battery report. 60,000 mWh = 60 Wh.

Full-charge capacity ÷ design capacity × 100. Enter 100% if capacity above is already the usable full-charge figure.

The charge percentage when you start using the laptop.

The charge you want to keep in reserve. Must be below the starting charge.

Your workload

Use a measured average battery-discharge reading if available. These editable examples are assumptions, not test results for a particular laptop.

Total laptop draw from the battery, not the wattage printed on the charger.

Creates a low/high estimate by varying power. It is not a measured confidence interval.

Electricity cost

Sleep, standby and external devices are not included.

A year is modelled as 365 days with this weekly pattern.

25p is an example, not a current UK tariff. Enter the unit rate on your bill.

90% is an editable assumption for converting laptop demand to wall power; the actual figure varies.

Your estimate

Let’s put numbers to it.

Your result appears here as you adjust the inputs.

What goes into the estimate?

Battery runtime

Usable energy = capacity × health × charge window. Runtime in hours is usable watt-hours divided by average watts. A 60 Wh battery at 100% health, used from 100% to 10%, has 54 Wh available: at 10 W, that is 5.4 hours.

The range changes average power by your chosen percentage. Brightness, video calls, GPU use, temperature and power settings can move the real result outside it.

Power and cost

Wall power = laptop power ÷ efficiency. kWh = wall watts × active hours ÷ 1,000. Cost = kWh × your unit rate. Standing charges are excluded.

Charging the battery and powering a running laptop can overlap. The separate charge-window cost is not added to annual active-use cost, which would risk counting the same energy twice.

Finding your battery capacity

On Windows, the built-in powercfg /batteryreport report lists design capacity and full-charge capacity. Convert mWh to Wh by dividing by 1,000. Health is full-charge capacity divided by design capacity. A charger’s 65 W or 100 W label is its maximum output rating, not continuous laptop consumption.

Method sources: Microsoft: powercfg and battery reports · Virginia Tech: estimating electricity use and cost. Reviewed 29 October 2026.

A few useful answers.

Why does my laptop last less than this estimate?

The average power you entered may be too low for your workload, or usable battery capacity may be lower than expected. Manufacturer runtime tests and this energy model are not measurements of your particular setup.

Can I enter my charger wattage?

Not for a useful runtime estimate. A charger rating is a maximum output capability. Use average total battery discharge power for the selected workload; the calculator applies your efficiency assumption separately for wall electricity cost.

Does battery health change the electricity estimate?

Health changes the energy available for the selected charge window and therefore runtime. Annual active-use electricity is based on workload power and hours, so it does not fall simply because an older battery stores less charge.

Make the next choice easier

Battery life is more than a bigger number.

Read what changes real-world runtime, then use the questionnaire to weigh battery life against your software and budget.

Find my matches →Read the Windows battery guide →Browse computers →