EV Tariff Comparison Calculator: Is Off-Peak Cheaper?
Compare an off-peak EV tariff with a flat electricity rate using your whole home's bill. Include household consumption, standing charges and charging losses, then find the off-peak charging share needed to break even. Use your own UK or Irish tariff quotes. Choose a car to load catalogue specifications. Other starting values are editable examples; use the rates from your bill.
Your inputs
When does an off-peak EV tariff beat a flat rate?
Illustrative annual scenario: 10,000 miles, 4 miles/kWh measured at the meter, all charging at home, 3,000kWh non-EV use entirely at peak rate. Peak 0.30, off-peak 0.10, flat rate 0.25 and both standing charges 0.50/day, in the selected currency. This is a calculation, not a supplier quote.
| EV energy at off-peak rate | Annual home bill | Saving vs flat rate |
|---|---|---|
| 0% | £1,832.50 | -£275.00 |
| 55% | £1,557.50 | £0.00 |
| 100% | £1,332.50 | £225.00 |
Frequently asked questions
Is an EV tariff worth it for low mileage?
Not always. Savings on a small amount of EV charging may be outweighed by a higher daytime price or standing charge. Compare the whole-home annual bill and the break-even off-peak share, not just the advertised night rate.
Does this comparison include standing charges?
Yes. It adds 365 daily standing charges to each scenario and includes non-EV household electricity separately. Public charging, exit fees and solar export income are excluded.
What if the cheap rate applies only to my EV?
Set household off-peak use to 0% and use the normal household rate as the peak rate. Enter the share of EV energy actually eligible for the discounted rate, subject to the supplier's rules.
Why does the calculator ask whether consumption includes losses?
A trip-computer figure normally describes battery use, while an electricity-meter figure already includes charging losses. Select the matching basis so those losses are not counted twice.
Guides for your charging decision
How this works
Driving electricity is distance divided by miles/kWh, or kilometres multiplied by kWh/100km divided by 100. One mile is exactly 1.609344 km. Apply the home charging share, then add charging losses only for battery-based consumption figures. EV and household consumption each use their own off-peak share. Total bill adds 365 daily standing charges. Enter VAT-inclusive rates. The comparison assumes a flat rate; no exit fees, export income or public charging costs are included. The break-even off-peak share solves for the EV share that makes both bills equal, holding household usage fixed; it is not a guarantee that your charging schedule can achieve that share. Negative unit rates are supported. Dynamic rates need interval consumption data and are not forecast here.
Technical references
- US Department of Energy: charging power and vehicle limits
- Energy Saving Trust: time-of-use tariffs and negative prices
- NIST: exact distance conversion factors
Keep the assumptions in view
Use the usable battery capacity and AC rating from your vehicle documentation. Use electricity prices from your current bill. Estimates do not replace an electrical survey or a supplier quote.
Calculations work without JavaScript. To share a scenario, copy the address after calculating. Avoid putting personal information in these fields.