An EV tariff can cut charging costs when the car can use its cheap hours. The smallest advertised price is not enough to prove that it will.
Compare the full annual result. Include wall energy, realistic timing and every fee that changes between plans.
Gather the figures from each offer
For a flat plan, record the price per kWh and the fixed annual charge. For a time-of-use plan, record the off-peak price, peak price, exact time windows and fixed charge.
Make sure the figures use the same basis. Check taxes and regulated network charges. A supplier may show an energy-only price beside another plan’s complete variable price.
Also read the rules for weekends, public holidays and seasons. Take screenshots or save the tariff sheet with its date. Offers change.
Estimate annual EV wall energy
Start with annual distance and real-world battery consumption.
For 15,000 km at 18 kWh per 100 km:
15,000 × 18 ÷ 100 = 2,700 kWh in the battery
The meter records more because charging is not perfectly efficient. At a 90% example efficiency:
2,700 ÷ 0.90 = 3,000 kWh from the wall
Use a measured wallbox or meter figure if you have one. It is better than estimating both consumption and losses.
Be honest about off-peak charging
A tariff may offer six cheap hours, but your car may need eight after a long day. A late arrival can leave only three. A household may also override schedules for an unexpected journey.
Review several months of charging times. Estimate what share of EV wall energy, not what share of sessions, would fit off peak. One large session crossing into peak hours matters more than several small sessions that fit.
Test a cautious case as well as an optimistic one. For example, compare 90%, 75% and 60% off-peak shares.
Calculate the EV cost under each plan
For a flat plan:
annual wall kWh × flat price + extra annual fee
For a two-rate plan:
wall kWh × (off-peak price × off-peak share + peak price × peak share) + extra annual fee
Only include fees that differ. If both plans have the same standing charge, it does not change the EV comparison.
Find the break-even off-peak share
Increase and decrease the off-peak share in the tariff calculator. The point where the result changes winner tells you how reliably your schedule must perform.
Then include the rest of the home
An EV-only plan can look attractive while making cooking, heating or hot-water electricity more expensive. Repeat the calculation using the home’s interval data if the peak price changes.
Check whether flexible loads can move. A dishwasher may be easy to schedule. Electric space heating may not be, especially on cold evenings.
Solar export payments can also differ between contracts. Keep self-consumption, import and export as separate lines rather than hiding them inside one EV estimate.
Flat, time-of-use or dynamic?
A flat tariff is simple. Every kWh uses the same variable price, so charging time does not affect the rate.
A time-of-use tariff has known bands. It suits drivers whose charging can reliably move into a cheap window.
A dynamic tariff changes more often. It can reward automation and flexibility, but the cheapest hour in an advert is not an annual average. Understand how prices are set, how much notice you receive and what happens if the app or connection fails.
EU electricity rules provide a framework for dynamic price contracts and consumer information, but the offers and protections you see depend on your country, supplier and meter setup.
Check the contract, not only the calculator
Read minimum term, exit fee, price-change rights, meter requirements and billing intervals. Confirm whether the wallbox or car integration is mandatory. Ask what happens when smart control is unavailable.
Treat promotional credit separately. A one-off bonus can change year one without making the tariff better in year two.
Do not send account credentials to an unknown charging app. Review permissions before connecting a car, wallbox or energy account.
A useful final comparison
Create three rows for each plan:
- EV charging under realistic timing.
- All other household import.
- Fixed fees and export value.
Run the result for a normal year and a difficult year with more peak charging. If one plan wins only under perfect behaviour, the saving may be fragile.
The best tariff is not the one with the lowest number in the advert. It is the one that costs less for the way your home and car actually use energy.
Frequently asked questions
Is the tariff with the lowest night rate always cheapest for an EV?
No. Fixed fees, a higher peak rate and charging outside the cheap window can outweigh a low headline rate.
Should I use the car's kWh per 100 km figure?
Use it as battery-side consumption, then account for charging losses to estimate the wall energy on your bill.
How can I estimate the share charged off peak?
Compare charging history with the proposed tariff hours. Include late arrivals, long sessions and days when the schedule is overridden.
What is a dynamic electricity tariff?
Its price changes by shorter time intervals, commonly linked to wholesale or market signals. Read the contract's price formula, notice rules and automation requirements.
