EV Charger Off-Peak Savings Calculator
Estimate how much a home EV tariff could save by moving charging from a peak electricity rate to a cheaper overnight rate.
Enter Your EV Charging Pattern
Your Off-Peak Saving
Enter your mileage, rates and off-peak share to estimate the saving.
How To Use The EV Off-Peak Calculator
1Use Home Miles
Enter the miles you normally recharge at home. If half your driving is covered by workplace or public charging, leave those miles out or run a separate comparison.
2Pick Efficiency
Miles per kWh varies with weather, speed, tyres and driving style. Use your car’s long-term average if available, not a single best day.
3Set Both Rates
Enter your current peak unit rate and the overnight EV rate you are considering. Do not forget that a cheaper night rate may come with a different daytime rate.
4Adjust The Share
Set the percentage of charging that will genuinely happen during the cheap window. A short off-peak window may not refill a large battery from low charge.
How To Read The Result
The main result is the yearly saving from charging the off-peak share at the cheaper rate instead of charging everything at the peak rate. The calculator includes charging losses because the grid energy bought from your supplier is higher than the energy that reaches the battery. A 10% loss means a car needing 10 kWh of battery energy may draw about 11.1 kWh from the supply.
The result is specific to the mileage, efficiency, off-peak share and rates you enter. It will be highest for drivers who cover many miles, charge most of those miles at home, have a clear price gap between day and night rates, and can schedule charging reliably. It will be lower if you already use little home electricity for the car or if most top-ups happen at public chargers.
Formula And Method
Battery kWh per year = weekly miles x 52 / miles per kWh.
Grid kWh per year = battery kWh / (1 – charging loss percentage).
Peak-only cost = grid kWh x peak unit rate.
Mixed tariff cost = off-peak kWh x off-peak rate + peak kWh x peak rate.
Annual saving = peak-only cost – mixed tariff cost.
Period saving after setup = annual saving x years – setup cost.
The default peak rate is an editable Ofgem price-cap style electricity unit-rate example for England, Scotland and Wales direct debit customers in the second quarter of 2026. Your actual tariff can differ by region, supplier, payment method and contract.
Worked Off-Peak Charging Examples
Low-Mileage Driver
At 80 miles a week and 3.8 miles per kWh, the annual home charging energy is modest. Even a large rate gap may save less than a broadband subscription, so standing charge changes and tariff restrictions matter.
Commuter With Reliable Overnight Charging
At 250 miles a week, 3.5 miles per kWh and 90% off-peak charging, the annual saving can be substantial. The result is strongest when the driver plugs in most nights and the charger starts automatically in the cheap period.
Short Cheap Window
If the cheap period is only four or five hours and the charger is 7 kW, a very low battery may not fully recharge. Lower the off-peak share to reflect any charging that spills into peak hours.
Tariff Checks Before Switching
Read the tariff information label before switching. The lowest overnight price is only one part of the decision; the day rate, standing charge, contract length, exit fees, smart-meter requirement and charger compatibility can all change the annual value.
| Check | Why It Affects Savings | What To Enter |
|---|---|---|
| Day rate | Some EV tariffs reduce the night rate but raise the day unit rate. | Use the peak rate you will actually pay after switching. |
| Standing charge | The daily charge may change and can offset part of the EV saving. | Keep it separate; this tool compares charging unit rates only. |
| Cheap window length | A short window may not cover the full charge. | Reduce the off-peak share if charging often continues after the window. |
| Smart charger rules | Some tariffs require a compatible charger, app or car connection. | Add setup cost if new equipment is needed. |
| Public charging | Rapid charging can cost far more than home charging and is outside this comparison. | Exclude miles not charged at home. |
FAQ
Does the calculator include the standing charge?
No. It compares EV charging unit rates only. Check the standing charge separately when comparing tariffs.
What charging loss should I use?
For many home charging estimates, 8% to 12% is a practical range. Cold weather, low-power charging and vehicle systems can change it.
Should I include solar charging?
If solar covers some EV charging, reduce the home grid miles or run a separate case with a lower effective rate. Export tariffs and battery storage need their own calculation.
Can I compare this with petrol cost?
This page focuses on peak versus off-peak electricity. Petrol comparison needs fuel price, miles per gallon, UK gallon conversion and servicing assumptions.
What if I have two EVs?
Add the weekly home-charged miles for both vehicles and use a weighted average efficiency if they differ.
Can the saving pay for a charger?
Enter the charger or tariff setup cost. The payback line shows how long the off-peak saving alone would take to recover that cost.
Sources
- Ofgem. (2026). Energy price cap explained. Ofgem. https://www.ofgem.gov.uk/information-consumers/energy-advice-households/energy-price-cap-explained
- GOV.UK. (n.d.). Electric vehicle smart chargepoints. Office for Zero Emission Vehicles. https://www.gov.uk/government/publications/electric-vehicle-smart-chargepoints
- Energy Saving Trust. (n.d.). Charging an electric vehicle. Energy Saving Trust. https://energysavingtrust.org.uk/advice/charging-electric-vehicles/