Computers & Laptops

Laptop Charging Cost Calculator

What one laptop charge costs and what that comes to over a month, counting the energy the meter sees.

10 inputs Free, no sign-up

Your figures

The Wh figure on the battery - the easiest way in, since laptop batteries are labelled this way.

Together with the voltage below, if your battery is marked in mAh instead. Capacity alone is not enough - mAh measures charge, not energy.

Required if you gave a capacity rather than an energy.

Leave blank for this page's 85% assumption. Charging loses energy as heat in the charger, the cable and the battery.

A full cycle. Two half-charges count as one.

Use fewer for something you only run at weekends.

Rupees per unit (kWh), from your own bill. Tariffs differ by state, by connection and by how much you use, so this is the figure the result is most sensitive to.

Try an example

Result

Your result

Enter your figures and the result appears here.

Estimates only. Rates, fees and specifications change. Confirm against the official source before you rely on a figure — see our disclaimer.

About this calculator

The energy that ends up in the battery is not the energy the meter counts. Charging loses something to heat in the charger, the cable and the cells, so a 56 Wh charge pulls around 66 Wh through the socket — and the socket figure is the one you pay for.

The answer is usually reassuringly small, which is itself worth knowing.

How to use this calculator

  1. Enter the battery's watt-hour figure, or its mAh and voltage.
  2. Say how many full charges a day, and how many days a month.
  3. Enter your electricity rate.

The formula

Energy from the socket = Battery energy / Charging efficiency
Cost per charge        = Energy from the socket / 1000 x Rate
Cost a month           = Cost per charge x Charges a day x Days a month
SymbolMeaningUnit
Battery energy Capacity in watt-hours Wh
Efficiency Share reaching the battery %
Rate Your tariff per unit ₹/kWh

Worked example

A 56 Wh battery at 85% efficiency, one charge a day, 30 days, at ₹8 a unit:

From the socket = 56 / 0.85      = 65.88 Wh
Per charge      = 0.06588 x 8     = 0.53
A month         = 0.53 x 30       = 15.81

About sixteen rupees a month — less than most people expect.

Notes and limits

  • This costs the charging only. Running the laptop from the mains is a separate and larger figure, and the laptop electricity cost calculator takes it.
  • A full cycle is a full cycle whether it happens in one go or in several top-ups. Counting every time you plug in would overstate it considerably.
  • The 85% is an assumption. A cheap charger is worse and a good USB-C one is better, and the result names whichever figure it used.
  • A battery that has aged holds less, so an old laptop costs slightly less per charge and needs more of them.

What this calculation assumes

  • Charging efficiency defaults to 85% and the result names it as an assumption.
  • A charge is counted as a full cycle from empty to full.
  • The battery is treated as holding its rated capacity.

Frequently asked questions

How much does it cost to charge a laptop?

A 56 Wh battery at ₹8 a unit costs about 53 paise a charge once charging losses are counted, or roughly ₹16 a month at one charge a day.

Why is the energy from the socket more than the battery holds?

Because charging is not lossless. Typically 10-15% of what the meter counts becomes heat in the charger, the cable and the battery rather than stored charge.

Is it cheaper to run on mains or on battery?

On mains, marginally - running from the battery means paying for the charging losses as well as the energy. The difference is small enough not to matter in practice.

Related calculators