Time-of-Use Rates

A time-of-use tariff does something very simple: it stops charging you one price for electricity and starts charging you several, depending on the hour. That is a mild inconvenience for most of a household and a straightforward win for an electric car, because charging is the only large load in the house whose timing genuinely does not matter to anybody. The car sits on the driveway for ten hours. Which of those hours it draws current in is a setting.

The size of the win is worth stating up front. Driving 12,000 miles a year at 3.5 miles per kWh consumes roughly 3,810 kWh at the meter once the 90 percent charging efficiency used across this site is applied. At the 16.5 cent national average that is about $629 a year. Move the whole lot into a typical off-peak window and it becomes about $377, which is roughly $251 back in your pocket for changing one setting.

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What is a time-of-use rate plan?

Electricity costs the utility different amounts at different hours because generation is dispatched in merit order. Cheap baseload runs constantly, and expensive peaking plant is brought on only when demand climbs. A flat residential rate averages all of that into one number and hides the variation. A time-of-use tariff exposes it, and in doing so gives you a financial reason to move flexible load out of the expensive hours.

Nothing physical changes at your house. The meter already records interval data on almost every modern installation, the wiring is identical, and the charger neither knows nor cares which tariff you are on. The only change is arithmetic applied to the same kWh at the billing stage.

EV-specific plans go a step further and set a deliberately low overnight price to encourage charging when the grid is underused. That is not generosity, it is grid economics: overnight demand troughs are genuinely cheap to serve, and a utility would rather sell you cheap energy at 2am than build capacity for 6pm. Where such a plan exists, it is usually the best residential rate available for any purpose.

What do peak, off-peak and super-off-peak actually mean?

The names are not standardised and neither are the hours. What is consistent is the shape: an expensive band in the late afternoon and evening, a cheap band overnight, and one or two transitional bands between them. Some solar-heavy grids have inverted part of the picture and now price the middle of the day very cheaply, because midday generation exceeds midday demand.

Two details in a tariff document matter more than the headline prices. The first is whether weekends and holidays are treated as off-peak, which many plans do and which quietly removes most of the inconvenience. The second is the exact boundary minute of the peak window, because a charger that starts fifteen minutes early is paying peak rates for the most expensive fifteen minutes of the day. Set the schedule to begin comfortably after the boundary rather than exactly on it.

What does charging cost per year in your state?

The table below runs the same model across every state: 12,000 miles a year, at 3.5 miles per kWh, with 90 percent charging efficiency, giving 3,810 kWh purchased. The off-peak column applies a typical EV plan differential where the off-peak price sits around 60 percent of the all-hours average. Averages hide a lot of variation between utilities within a state, so treat this as a comparison rather than a bill.

The spread is the headline. North Dakota sits at 11.1 cents and an annual charging bill of about $423. Hawaii sits at 41 cents and about $1,562 for exactly the same driving. That is a difference of roughly $1,139 a year between two households with identical cars and identical mileage, which is why national averages are close to useless for a personal decision.

The cents per mile column is the number worth remembering, because it is directly comparable to a petrol figure. At the 16.5 cent average the cost is 5.2 cents a mile. A 30 mile per gallon car at four dollars a gallon is 13.3 cents a mile. The full comparison across rates and vehicle efficiencies is in the electricity rates by state chart and the cost per mile calculator.

What is the off-peak differential actually worth?

Everything in the saving column above rests on one assumption: that the off-peak price is around 60 percent of the all-hours average. That is a reasonable middle figure across published EV tariffs, but the real differentials range from mild to dramatic. Some plans price off-peak at 80 percent of average, which barely justifies the paperwork. Others price a narrow overnight band at a third of the average, which turns a modest saving into a substantial one.

Because the saving scales with the rate, the states where the switch matters most are the expensive ones. A household in Hawaii moving every session off peak saves about $625 a year on the same assumption. A household in North Dakota saves about $169. Both are worth having, but only one of them justifies buying a connected charger specifically to guarantee the timing.

Run your own differential rather than the generic one. Take the off-peak price and the peak price from your tariff sheet, put them into the time-of-use savings calculator with your real mileage, and you will get a number you can actually act on. If the answer is under a hundred dollars a year, the plan is probably not worth restructuring your household around.

Whole-home TOU or a separately metered EV rate?

These are two genuinely different products and confusing them is the most expensive mistake on this page. A whole-home time-of-use plan reprices every kilowatt-hour the house consumes. A separately metered EV rate reprices only the energy that passes through the charging circuit, and leaves the rest of the house on whatever tariff it was already on.

Whole-home plans are free to join, available almost everywhere, and carry the risk described in the next section. Separately metered EV rates carry no such risk, often have the lowest price per kWh available to a residential customer, and cost real money to set up, because a second meter or an approved submeter and the associated service work is not a trivial addition to the install. Where the utility offers both, the decision is a straightforward payback calculation: divide the metering cost by the annual difference in savings and see how many years it takes.

One practical wrinkle: a separately metered arrangement usually constrains what can be on that circuit, which normally means one dedicated charging circuit and nothing else. That interacts with any plan to add a second charger later, so mention the second car to the utility before the meter goes in rather than afterwards.

When does a whole-home TOU plan cost you money?

Honestly and frequently, and this is where the savings tables published by utilities become misleading. Those tables show the charging saving. They do not show what happens to the other eighty percent of your consumption when it gets repriced.

The households that lose are recognisable. Somebody works from home and runs air conditioning through the hottest and most expensive hours. The cooking is electric and dinner happens squarely inside the peak window. There is a pool pump, a well pump, an electric water heater without a timer, or a heat pump cycling hard through a summer afternoon. Add those up and the peak energy premium can exceed the overnight charging saving without anybody noticing until the bill arrives.

The test is simple even if it takes an evening. Download a year of interval data from your utility account, which almost every utility now provides, and split your consumption by the hours the tariff defines. Apply the peak and off-peak prices to your own historical usage. If the answer is close, stay where you are, because a marginal saving is not worth reorganising when the dishwasher runs. If the answer is clearly positive even before the car, switch.

A middle path exists and is underused. Move the flexible loads first and switch tariffs second. A water heater on a timer, a dishwasher started at bedtime and a charger with a schedule together move enough consumption that the tariff arithmetic often flips from marginal to obvious.

Seasonal shoulder periods, and why they catch people out

Most utilities run at least two seasonal versions of the same tariff. The cooling season carries a longer and more expensive peak, because that is when the system is stressed. The rest of the year has a shorter peak, a lower peak price, or occasionally a completely different window shape. A few grids with heavy solar penetration have a mild midday super-off-peak in one season and none in the other.

The trap is that a charging schedule set once does not move when the tariff does. A window that starts at 9pm and was comfortably off-peak in the mild season can be sitting inside a peak that runs until 10pm in the cooling season. Nothing warns you. The bill goes up by a modest amount, which is exactly the size of increase people attribute to the weather.

Two defences work. Either set the charging window to the most conservative boundary across all seasons and accept a slightly later start year round, or diary a twice-yearly check when the seasonal schedule changes. The conservative window costs you nothing, because a charge that finishes at 5am is exactly as useful as one that finishes at 3am.

Do residential plans ever have demand charges?

A few do, and they behave in a way that surprises people who have only ever paid for energy. A demand charge bills your highest sustained power draw during the billing period, usually measured over a fifteen minute interval, and it is billed per kilowatt regardless of how long that peak lasted. Total consumption barely enters into it.

An EV charger is unusually good at setting a demand peak, because it draws a large constant load for hours rather than cycling. A 48 amp station delivering 11.5 kW alongside an electric range and an air conditioner can establish a monthly peak in a single evening that costs more than the energy did.

Where a demand charge exists, the response is different from the usual advice. Reducing charger output matters, because a 24 amp setting halves the contribution to the peak and still recovers a normal day of driving overnight. Staggering large loads matters. And a listed load management device becomes a financial tool rather than only a code one, since preventing coincident peaks is exactly what it does.

How do you make sure every session lands in the window?

A tariff only pays if the charging actually happens inside the cheap hours, and the most common failure is two systems each holding a schedule and cancelling each other out. Let exactly one own the timing. In most households that is the car, because it knows the state of charge and the departure time; where a utility program validates from station data instead, it is the charger. The full argument is in smart charging and scheduling.

Whichever you choose, verify the outcome once. A single morning spent checking that the session started when you expected is worth more than any amount of configuration confidence. Charger apps such as the one behind the ChargePoint HomeFlex hardwired station report per-session start times, and the Emporia 48 amp charger reports the same at a lower price. If you want the whole picture rather than the charging circuit alone, a panel monitor such as the Emporia Vue 3 with sixteen sensors shows which household loads are landing in your peak window, which is the data that tells you whether a whole-home plan will work.

How to read your own tariff sheet in ten minutes

Find four things and you have everything this page needs. The peak price per kWh and the exact hours it applies. The off-peak price and its hours. Whether weekends and holidays count as off-peak. And whether any fixed monthly charge differs between the plan you are on and the plan you are considering, because a higher standing charge can quietly erase a modest energy saving.

Then multiply. Your annual mileage divided by your car's miles per kWh, divided by 0.9 for charging efficiency, gives kWh purchased. Multiply by the off-peak price for the optimistic case and by the flat rate for the current case. The difference is your real number, and the charging cost calculator will do it for you if the arithmetic is tedious.

Ignore any comparison that quotes only the peak price. Utilities occasionally market EV plans by contrasting the off-peak price against a flat rate while omitting what the peak price does to the rest of your consumption. The honest comparison uses your own annual usage profile on both tariffs.

Where to go next

If your rate is high and the differential is wide, the next question is whether generating your own daytime energy changes the picture, which is covered in solar and battery EV charging. If your rate is low, the more useful comparison is against public charging, because home charging at 5.2 cents a mile is usually a fraction of the equivalent public price. That one is in home versus public fast charging.

Common questions

What does a time-of-use rate plan actually change?

It replaces one price per kWh with several prices that depend on when the energy is used. The amount of energy you buy does not change and neither does the meter; only the price attached to each hour does. For an EV owner that is close to free money, because charging is the one large household load whose timing is completely flexible and can sit entirely inside the cheapest hours of the day without anyone noticing.

How much does an EV rate plan save per year?

Driving 12,000 miles a year at 3.5 miles per kWh needs roughly 3810 kWh at the meter once the 90 percent charging efficiency figure is applied. At the 16.5 cent national average that is about 629 dollars. A typical off-peak price around 60 percent of the all-hours average brings it to roughly 377 dollars, so the saving is about 251 dollars a year. High-rate states save considerably more.

Can a time-of-use plan cost me more than a flat rate?

Yes, and this is the part utilities do not lead with. A whole-home plan reprices everything, not just the charger. A household with someone home during the day, electric cooking, a pool pump or air conditioning running through a hot afternoon can pay more on peak energy than it saves on off-peak charging. Compare a full year of your own usage by hour before switching, not just the charging portion.

What is a separately metered EV rate?

It is a second meter or submeter serving only the charging circuit, billed on its own tariff. The advantage is that the rest of the house stays on whatever plan already suits it, so there is no risk of repricing your daytime load. The disadvantage is install cost, since the metering hardware and the separate service arrangement can add several hundred dollars to a job that would otherwise be a straightforward branch circuit.

Do residential plans have demand charges?

Some do, and they behave very differently from energy charges. A demand charge bills your highest brief power draw in the month rather than total energy, so a single 11.5 kW charging session coinciding with an oven and an air conditioner can set the charge for the whole month. Where a demand charge exists, reducing charger output or staggering large loads matters more than the total kWh you consume.

What is a shoulder period and why does it catch people out?

Many tariffs run different windows by season, with a longer and more expensive peak through the cooling season and a milder structure the rest of the year. Shoulder periods are the transitional months where the schedule shifts, often by an hour or two at each end. A schedule set once and never revisited can drift into peak pricing simply because the tariff moved underneath it, which shows up as a bill nobody can explain.

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.