Time-of-Use Savings Calculator for EV Charging

This is the highest-return change available to most home charging households, and it costs nothing. If your utility offers a time-of-use or dedicated EV tariff, moving every charge into the off-peak window is free money, because the car is parked overnight regardless. The only requirement is scheduling, which every electric car can do from its own dashboard.

The saving is simply the rate gap multiplied by your annual charging energy. At a 13 cent spread and 3,810 kWh a year, which is what 12,000 miles at 3.5 miles per kWh works out to once losses are included, that is about 495 dollars a year.

=

Time-of-use savings

Rate gap x kWh

Models both sides honestly: what charging saves off peak, and what the rest of your household usage may cost you on a time-varying tariff.

Annual mileage

miles

Vehicle efficiency

mi per kWh

On-peak rate

Off-peak rate

Your current flat rate

What you pay now, before switching. Used to work out whether the switch is a net win overall.

cents per kWh

Household usage excluding the car

kWh per year

Share of household usage on peak

%

Net annual change

$372

Better off switching

Saved on charging

$495

Change on household usage

-$123

Charging energy billed

3,810 kWh

Cost per mile, off peak

3.5 cents

Saved over ten years

$3,720

Why this works so well for charging specifically

Time-of-use tariffs exist because generating capacity is expensive to build for peaks that occur a few hours a day. Utilities price accordingly, charging more when demand is high and less overnight when plant would otherwise be idle.

Most household loads cannot move. You cook when you are hungry and heat the house when it is cold. EV charging is the rare large load that is completely indifferent to when it happens, because the car sits unused for eight to twelve hours every night and only needs to be full by morning.

So charging is the ideal candidate for rate arbitrage. You move the largest discretionary load in the house into the cheapest hours, with no behaviour change beyond setting a schedule once. That is why this page exists and why it sits above almost every hardware decision on the site in terms of return.

What the spread is worth, at typical tariffs

The rule of thumb: a spread of eight cents or more is clearly worth acting on for a typical driver, and below about four cents it is marginal once you account for the risk of paying more on household usage. Above fifteen cents it is one of the best returns available on any household decision, because it recurs every year with no capital cost.

The trap: the rest of your house

Here is the part most articles skip. A time-of-use tariff does not simply add a cheap overnight rate to your existing bill. It replaces your flat rate with two rates, and the on-peak rate is usually higher than the flat rate you were paying.

So a household that uses a lot of electricity during peak hours can lose more on cooking, cooling and laundry than it gains on charging. Whether the switch is a net win depends on the ratio between your charging energy and your peak-hours household energy, which is why the calculator asks for both.

Rough guide. A household charging 3,800 kWh a year with modest daytime usage almost always wins. A household charging 1,500 kWh a year in a house with electric heat, air conditioning and someone home all day may not. The way to find out for certain is to look at your usage by hour, which most utilities now publish in their online portal, or to measure it directly with a circuit-level energy monitor.

There is a third option that removes the risk entirely: a separately metered EV tariff, where the charger circuit has its own meter and its own rate and the rest of the house is untouched. It adds the cost of a second meter and its installation, so it suits high-mileage drivers in wide-spread markets. Ask your utility whether one exists; many do not advertise it.

You do not need a smart charger for this

Worth stating plainly, because it is often implied otherwise. Every electric car sold can schedule charging from its own screen or app: set a start time, or set a departure time and let the car work backwards. That covers the entire savings case with no additional hardware.

What a smart charger adds is visibility and reporting. You can see how much energy went into the car and when, which turns "I think I am saving money" into a number. Some utility programmes also prefer charger-side control and pay a bill credit for enrolling, which is a separate saving worth checking for.

One practical warning. If both the car and the charger have schedules configured, they can conflict in ways that are genuinely confusing: the car waits for its window, the charger waits for its window, and the overlap is smaller than either. Set the schedule in one place only. This is the most common home charging support question and it is covered in smart charging and scheduling.

Check that the window fits your charge

An off-peak window is typically six to ten hours. Before switching, confirm your normal charge fits inside it.

Most drivers are comfortable. A 40 mile day needs about 12 kWh, which at 9.6 kW takes 80 minutes. But a high-mileage driver with a large pack and a modest circuit can genuinely overrun. Someone needing 50 kWh on a 7.7 kW charger takes over seven hours, which may not fit a six hour window, and the overflow charges at the peak rate.

That is one of the few situations where a larger circuit produces a direct financial return rather than just convenience, since it lets the whole charge land inside the cheap window. Work out your own time on the charge time calculator, and if it does not fit, the hardwired 48 amp buildout is the version that usually does.

Watch for demand charges

Uncommon on residential tariffs but not unknown. A demand charge bills you on your highest draw in any fifteen-minute period during the month, regardless of how much total energy you used. A 48 amp charger pulling 11.5 kW can set that peak on its own, and a demand charge can wipe out the entire energy saving.

Where one exists, the fixes are a lower charger output, or a load management device that prevents the charger from running at the same time as other large loads. Read the tariff sheet before switching, and if the phrase "demand charge" appears anywhere on it, model that separately.

Where to go next

Get your baseline cost on the charging cost calculator, check the window fits on the charge time calculator, and read time-of-use rates for how these tariffs are structured and what to ask your utility. If a utility programme requires charger-side control, the smart charger roundup covers which units support it.

Common questions

How much does a time-of-use rate save on EV charging?

For a driver covering 12,000 miles a year at 3.5 miles per kWh, moving charging from a 24 cent peak rate to an 11 cent off-peak rate saves about 495 dollars a year. The saving scales directly with the gap between the two rates and with your mileage, and it requires nothing but scheduling the charge to start after the off-peak window opens.

Is a time-of-use rate always worth switching to?

Not always, because the on-peak rate is usually higher than the flat rate you are leaving. Charging moves entirely off peak, so it always wins, but the rest of your household usage may not. A household that cooks, runs air conditioning and does laundry during peak hours can lose more on those than it gains on charging. Model both sides.

Do I need a smart charger to use an off-peak rate?

No. Every electric car sold can schedule charging from its own dashboard or app, which covers the entire case. A smart charger makes the schedule easier to see and gives you consumption reporting, and some utility programmes prefer or require charger-side control, but a scheduled charge from the car is functionally identical.

What is a separately metered EV rate?

Some utilities offer a dedicated meter and tariff for the charger circuit alone, so the rest of the house stays on its existing rate. That removes the risk of losing money on household usage, but it adds the cost of a second meter and its installation, so it pays off mainly for high-mileage drivers in areas with a large rate spread.

Are there demand charges to worry about?

On most residential tariffs, no. A few utilities apply a demand charge based on your highest fifteen-minute draw, and a 48 amp charger can set that peak on its own. Where a demand charge exists, a lower charger output or a load management device that staggers the charger against other large loads can be worth more than the energy saving.

What if my off-peak window is too short?

Check it against your actual charge time. A driver needing 12 kWh a night at 9.6 kW takes about 80 minutes, which fits any off-peak window. Someone needing 50 kWh at 7.7 kW takes over seven hours, which may not fit a six hour window. That is one of the few cases where a larger circuit produces a direct financial return.

Getting your own panel and load numbers ready for an electrician? The EV Home Charging Install Planner is the paid version of these pages: 8 printable worksheets you fill in with your own numbers, plus the full PDF, $29.