How to schedule EV charging for off-peak hours

A good EV charging schedule answers two questions: when must the car be ready, and when is electricity cheaper under your actual contract?

Work backwards from departure. Do not simply copy midnight as a start time and hope the session fits.

Start with the energy needed

Take the usable battery capacity and the change in state of charge.

A 60 kWh battery going from 30% to 80% needs 30 kWh in the battery:

60 × (80 − 30) ÷ 100 = 30 kWh

Charging losses mean the wall supplies more than this. At an example efficiency of 90%, the session draws about 33.3 kWh. Real efficiency varies by car, power and conditions.

The target itself should come from the vehicle’s guidance and your next journey. Do not apply 80% blindly to every battery.

Use effective power, not the wallbox badge

The charging rate is limited by the weakest relevant part of the setup. An 11 kW wallbox and a car that accepts only 7.4 kW AC produce at most 7.4 kW before other limits.

Dynamic load balancing may reduce that further while a heat pump, cooker or other building load is active. Some vehicles also draw less power because of temperature or battery conditions.

Estimate duration as:

battery energy to add ÷ (effective power × efficiency)

For 30 kWh into the battery at 7.4 kW and 90% efficiency, the estimate is about 4 hours 30 minutes.

Check the tariff window precisely

“Night rate” can hide important details. Write down:

• the exact start and finish time;
• whether weekends use different hours;
• whether winter and summer schedules differ;
• the peak price if a session runs over;
• fixed fees attached to the tariff;
• whether the supplier can change dynamic prices at short notice.

A five-hour cheap window cannot contain a seven-hour charge. The car will either finish later at another rate or stop short if the schedule blocks peak charging.

Choose one main scheduler

Many cars can schedule charging. Many wallboxes can do the same. Supplier or energy-management apps may add a third control.

Multiple timers can conflict. The wallbox may wait until 01:00 while the car allows charging only until 01:00. Each device appears to work, but no energy moves.

Choose one system to control the main window. Leave the other ready to supply or accept power. If a smart tariff requires its own integration, follow that provider’s setup and check the first sessions closely.

Start time or ready-by time?

A ready-by setting can be easier. You tell the car when you plan to leave, and supported vehicles calculate when charging should begin. Some also prepare the cabin and battery near departure.

A fixed start time gives you direct control of a tariff window. It also makes you responsible for ensuring the session is long enough.

Use the method your equipment supports reliably. If the ready-by calculation does not know your tariff, check that its chosen start falls inside the cheap period.

Add a sensible buffer

A calculator assumes steady power. Real homes are less tidy. Load management can reduce EV power. A cold car can use energy for battery conditioning. A temporary communication fault can delay a smart session.

Add 30 to 60 minutes for an ordinary overnight plan, or more where the power budget often changes. The right buffer depends on the importance of the trip and your experience with the setup.

Do not solve a short tariff window by raising electrical limits yourself. Charger current, circuits and protective devices must stay within the installed design.

What if the charge does not fit off peak?

You have four honest options:

1. Start before the cheap window and pay the peak rate for part of the session.
2. Finish after it, if the contract and controller allow that.
3. Use a lower target when the next journey needs less energy.
4. Ask a qualified installer whether a higher appropriate AC power is possible.

Compare the money before buying hardware. A larger wallbox does not help if the car or property supply remains the limit.

Review the result after a week

Look at the wallbox, car or meter history. Did sessions start on time? How many kilowatt-hours landed in the peak period? Was the car ready? Did household loads reduce power?

Then adjust the window or buffer. Scheduling is not a one-time theory exercise. A small correction based on real data is better than an elaborate plan based on guesses.

The best schedule is boring: plug in, wake up, and find the car ready at a cost you expected.