Charging an EV on a Time-of-Use Rate

Most of the money in home EV charging is not in which charger you buy. It is in when the electricity moves.

If your utility bills you on a time-of-use tariff, the same kilowatt-hour can cost substantially more at six in the evening than it does at one in the morning. Your car sits in the driveway for twelve hours either way. Moving the charge from the expensive hours to the cheap ones changes nothing about your day and can change your bill considerably — and it costs nothing to set up.

Why utilities price by the hour

Electricity is generated and consumed in the same instant. A utility has to have enough generation and enough wire in place to meet the highest demand of the day, and that peak is expensive to serve — it means running the least efficient plants and building capacity that sits idle the rest of the time.

Time-of-use pricing pushes that cost back to the people creating it. Peak periods, typically in the late afternoon and early evening when people come home and turn everything on, are priced high. Overnight, when demand falls away and there is spare capacity everywhere, power is cheap.

An EV is an unusually good fit for this, for one reason: it is a large, deferrable load. You cannot move dinner. You can move a charging session by six hours without noticing, because the car only needs to be full by the time you leave, not by the time you walk indoors.

Finding your own numbers

Everything here depends on rates that are specific to your utility, your plan and often your season, so this is a method rather than a table of numbers. Four steps:

1. Find your rate schedule.It is on your bill and on your utility’s website. You are looking for the peak and off-peak prices per kWh and the hours each applies. Note whether the schedule differs at weekends and by season — summer peaks are often both higher and longer.

2. Include delivery charges. This is the step people skip, and it distorts every estimate. Many bills split the supply price from delivery or distribution charges, and the delivery portion is frequently a large share of what you actually pay per kWh. Add anything charged per kilowatt-hour, not just the headline energy rate.

3. Work out your monthly kWh.Miles driven per month divided by your real efficiency in miles per kWh. We use 3.5 mi/kWh as a stated reference across the site, but use your own if you have measured it — and note it should be measured at the wall, not from the car’s display, because the car excludes charging losses. Our energy monitoring guide explains that gap and how to measure around it.

4. Multiply out both scenarios. Monthly kWh times the peak rate, and monthly kWh times the off-peak rate. The difference is your annual saving divided by twelve, and for most drivers on a genuine time-of-use plan it is the single largest lever available. Our cost-to-charge guide has a calculator for the base arithmetic.

The trap: the rest of your house

Here is the part that gets glossed over in EV forums. Switching to a time-of-use plan does not only expose your charging to hourly pricing. It exposes everything you own to it.

Your oven, your dryer, your air conditioning and your evening lighting all run during exactly the hours the utility has priced highest. If your household is home in the evenings and uses a lot of power then, the peak-rate penalty on the rest of your consumption can eat a meaningful share of what you save on the car — and in some households it can wipe it out entirely.

Two practical implications. First, compare plans using your whole annual consumption, not just the EV load; most utilities publish a comparison tool that uses your actual interval data, which is far better than any estimate. Second, check whether the plan has a minimum term before you can switch back, because some do.

Some utilities also offer a dedicated EV tariff or a separately metered EV circuit, which prices the car’s consumption independently of the house. If that exists where you are, it removes the trap entirely and is usually the better answer — the separate meter costs something to install, so weigh that against the saving.

Setting it up, and the one mistake to avoid

You need the charging to happen in the cheap window without you thinking about it. There are two places to arrange that, and you should use exactly one:

In the car.Essentially every EV sold in the last decade supports a scheduled start or a departure time. It is free, and the schedule travels with the vehicle, so it still works at a relative’s house or a holiday rental.

In the charger.Any smart charger can do the same thing. Useful if your car is older, or if you want the charger’s energy data broken out by session.

The mistake is doing both. When the car and the charger hold different schedules, the overlap can be small or nonexistent and you come out in the morning to a car that did not charge, with nothing obviously broken. It is one of the more common causes in our troubleshooting guide. Pick one, turn the other off entirely, and check it for a couple of nights.

One refinement worth knowing: if your peak window ends at, say, 9pm, do not set every large appliance to start at 9pm. A whole neighborhood of EVs starting simultaneously is exactly the behavior that leads utilities to redesign these tariffs. If your car or charger supports a randomized start or a departure-time mode that spreads the session, use it.

Does the charger matter at all here?

Less than you would think. A time-of-use strategy needs the charge to fit inside the cheap window, and that is the only place charger speed enters the picture.

A Level 2 charger at 40 amps adds roughly 34 miles of range per hour at our 3.5 mi/kWh reference, so a typical daily top-up fits into a short off-peak window several times over. A Level 1 charger at around 5 miles per hour may not: if you need 40 miles back and your off-peak window is six hours, Level 1 will still be charging when the expensive rate returns.

So the honest framing is that time-of-use pricing is one of the better arguments for Level 2 — not because it is faster in a way you notice, but because it finishes inside the cheap hours. Our do you need Level 2 guide weighs that against the install cost, and our main roundup covers the field if the answer is yes.