How Our EV Calculations Work

Battery energy, supplied energy and cost

We use usable battery capacity and the positive change in state of charge. Charging losses are a percentage of supplied energy, not an uplift on stored energy.

For a 60 kWh usable battery going from 20% to 80%, 36 kWh reaches the battery. At 10% losses, that requires 40 kWh supplied. At £0.30/kWh the energy cost is £12; adding a £1 session fee makes the estimate £13. Calculation uses unrounded values, with rounding for display.

Use the calculator’s separate loss assumptions for socket, AC and DC charging as appropriate. How to choose a charging-loss allowance explains the measurement boundary and why measured values vary.

How charging time is estimated

AC: supplied energy is divided by the effective charging power. The car’s AC limit, charger rating and supported connector/supply restrictions can cap that power. For 40 kWh supplied at a constant 7.4 kW, the estimate is 5.405 hours, or about 5 hours 24 minutes.

DC: the model uses separate average-power stages up to 80% and above 80%, capped by the effective charger and vehicle limits. Automatic settings use a matching manufacturer charging-time reference where available to estimate the lower stage; otherwise they start from 65% of the vehicle’s DC peak. The upper stage starts from 25% of peak. These are model assumptions, not measured charging curves, and the average-power inputs can be adjusted.

A reference is only used when it matches the configured battery and DC limit. It does not guarantee the published charging time under different starting percentages, temperatures or charger conditions. The simple two-stage model cannot reproduce every vehicle’s taper.

By charging time: the model works through the available time and estimates energy gained and ending percentage. It stops at full charge and counts only the energy required. Charging losses reduce the power reaching the battery.

Queueing, connection/authentication, unexpected power sharing and a detailed temperature model are outside the estimate. Allow practical margin when planning a journey.

Range and EV versus petrol or diesel

Efficiency is based on battery energy, internally in miles per kWh. Where catalogue efficiency is derived from published range and usable capacity, it is a planning estimate; it is not a promise of real-world range. You can enter your own efficiency or full-charge range.

For 100 miles at 4 miles per battery kWh, 10% losses and 30p/kWh, electricity costs £8.33. At 45 imperial MPG and £1.50/litre, fuel costs £15.15. The difference is £6.82 for that distance and those assumptions.

An imperial gallon is 4.54609 litres; a US gallon is 3.785411784 litres. One mile is 1.609344 kilometres. Use the correct MPG unit. Changing distance units preserves the physical distance. A period label such as “monthly” describes the distance you entered; it does not multiply it automatically.

The comparison covers driving energy costs. Purchase price, depreciation, finance, servicing, insurance, tax and charging-equipment installation are not included. Efficiency derived from electricity-meter readings already includes charging losses: do not apply that allowance a second time.

Prices, fees and changing tariffs

Enter your actual electricity and fuel prices. Example rates are not market averages or live offers. Currency selection changes labels; it does not convert money or fetch exchange rates.

A charging estimate uses the flat electricity rate you enter for that session. If charging crosses a tariff boundary, calculate each portion separately at the applicable rate and add the costs. Account for a session fee once, not once per portion.

Parking, idle/overstay charges, subscriptions and household standing charges are not automatically included. Add any applicable extra costs when comparing the final bill. A charger-discovery price can have payment, membership, timing and freshness conditions; check the displayed qualifications and the operator’s terms.

Vehicle data and saved estimates

Choose the right model and specification in My EVs, then check the charging figures. Usable and gross capacity are different. Vehicle descriptions can include sourced values, qualified estimates and editable assumptions; an unknown value should not be treated as a verified specification.

Calculate and Compare hold independent scenario inputs. “View in Calculate” deliberately transfers a comparison scenario to Calculate. Saved estimates keep their assumptions rather than silently acquiring newer prices or vehicle values. Check the saved rate and inputs before reusing an old estimate.

Weather, speed, route, load, battery condition and accessory use affect real-world range. A figure rounded to two decimal places is not evidence that the underlying assumption is that accurate.

How to investigate an unexpected result

1. Check units and capacity. Confirm usable kWh, kW, the price unit, and imperial versus US MPG.
2. Check the session. Confirm starting percentage, ending percentage or time, charging type and loss allowance.
3. Check the boundary. Compare supplied energy with supplied energy, not with battery energy. Compare the energy charge separately from other bill items.
4. Check the assumptions you saved. An old rate, a custom charging-power override or a different configured EV can explain a difference.
5. Send a reproducible correction. Email help@evcalculated.com with the calculator view, vehicle specification, non-sensitive input values, expected result and actual result. Include a source link when reporting a vehicle-data issue.

These methods describe the current calculator. External charging guidance supports the explanation of real-world limitations; it does not validate every vehicle record or certify individual results.