EV Charging Cost Calculator
Estimate session cost from battery size and state of charge.
EV Charging Cost Calculator
EV charging cost estimates what you pay to add energy to your car's battery from state of charge (SOC) start to end, accounting for charger efficiency losses. The inputs are pack size in kWh, start and end SOC percent, your electricity rate, and charging efficiency.
Energy stored in the battery is less than what the meter draws—the onboard charger and AC conversion lose heat. This calculator divides battery kWh added by efficiency to get grid kWh, then multiplies by your $/kWh rate for session cost.
Use it to compare home charging vs public rates, size solar for an EV load, or budget monthly driving cost. Pair with appliance cost or electricity bill calculators for whole-home context.
How this calculator works
- Enter battery pack size in kWh (usable capacity from specs—check EPA or manufacturer, not always nameplate).
- Enter start SOC and end SOC as percent (e.g. 20% to 80% for a typical daily charge).
- Battery kWh added = pack kWh × (end % − start %) ÷ 100.
- Set charging efficiency (default 90%)—home Level 2 often 0.85–0.92 depending on vehicle and cable.
- Grid kWh = battery kWh ÷ efficiency. Session cost = grid kWh × $/kWh rate.
Core charging cost relationships
Battery kWh = pack × (end % − start %) | Grid kWh = battery kWh ÷ η | Cost = grid kWh × $/kWh
SOC delta times pack size is energy stored in the traction battery. The grid supplies more than that because charging converts AC to DC with losses. Efficiency η (eta) is the fraction of grid energy that reaches the pack—typical home charging 85–92%. Cost applies to grid kWh, what your utility meter or public charger bills.
Formulas used by this tool
- Battery kWh added = pack size × (end % − start %).
- Grid kWh = battery kWh ÷ charging efficiency.
- Session cost = grid kWh × $/kWh rate.
Worked example: 75 kWh pack, 20% to 80%
A 75 kWh EV charges from 20% to 80% SOC at $0.14/kWh with 90% charging efficiency.
- SOC delta = 80% − 20% = 60%. Battery kWh added = 75 × 0.60 = 45 kWh.
- Grid kWh = 45 ÷ 0.90 = 50 kWh drawn from the wall.
- Session cost = 50 × $0.14 = $7.00 for this charge.
- A full 0–100% charge would use more grid kWh and cost more—many owners avoid 100% daily for battery longevity.
Practical tips
- Use usable kWh, not gross pack marketing size, when specs distinguish them.
- Public DC fast charging bills per kWh or per minute—enter your effective $/kWh for comparison only.
- Off-peak TOU rates: use the rate for hours you actually charge overnight.
- Solar offset: compare session cost at retail rate vs fuel cost per mile for gas vehicles.
- Lower efficiency (older EVSE, long cable, cold weather) increases grid kWh for the same SOC gain.
Frequently asked questions
What is state of charge (SOC)?
SOC is how full the battery is as a percentage. 20% means 20% of usable capacity remains; charging to 80% adds 60 percentage points of pack energy. Enter start and end from your app or dashboard.
What charging efficiency should I use?
Home Level 2 AC charging often lands around 0.88–0.92. DC fast charging efficiency can differ. Use 0.90 as a default; lower it if you know your setup is lossy or in cold weather.
Why is grid kWh higher than battery kWh?
Charging loses energy as heat in the EVSE, cable, and onboard converter. If efficiency is 90%, the grid must deliver 1.11 kWh for every 1 kWh stored. You pay for grid kWh, not pack kWh.
Does this include public fast-charging fees?
Enter an effective $/kWh that blends energy and session fees if needed. Some networks charge per minute at high power—convert a typical session to $/kWh for this model or use your receipt total divided by kWh delivered.
How do I estimate monthly EV charging cost?
Run this calculator for a typical charge (e.g. 20–80% daily), then multiply session cost by charges per month. Or multiply monthly miles ÷ efficiency (mi/kWh) × $/kWh for a driving-based estimate.
Can solar power my EV charging?
Yes. Session grid kWh is the load solar can offset. Size arrays using daily driving kWh plus home loads. Enter your retail $/kWh to see dollars saved when solar covers EV charging during sunshine or stored in a home battery.
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