What changes on a time-of-use plan
On a standard plan a kWh costs the same at 6 pm as at 3 am (or rises only with how much you use in the month). On a time-of-use (TOU) plan the price depends on the clock: a peak window, usually on weekday late afternoons and evenings when the grid is most loaded, costs more, and the rest of the day costs less than the standard price. The utility is not giving anything away: rate designers usually aim for a customer with an average load profile to pay about the same on either plan, so the saving comes from using less than average in the peak.
That makes the question personal, but it can be measured. For each utility below we took its cheapest time-of-use plan open to any household and its cheapest standard (flat or tiered) plan, and priced a full year for the same typical home in that state: monthly use from EIA, spread over the hours with NREL’s ResStock load shape for the state’s single-family homes. Then we moved part of the use out of the most expensive hours of each day and priced it again.
Without changing anything
Switched with no change in habits, the typical home paid $10 more a year on time-of-use at the median utility. The range is wide: at Central Hudson (New York) the SC6 plan cost $357 less than SC1; at Dominion Energy SC (South Carolina) Rate 5 cost $147 more than Rate 8. Where time-of-use wins with no effort, the utility has usually set its off-peak price well below the standard rate and kept the peak window short; where it loses, the peak covers the hours when a typical home runs its air conditioning, cooking and laundry.
Moving use out of the peak
The levers are the loads with a timer or some slack: an EV, the dishwasher, the clothes washer and dryer, an electric water heater, a pool pump, and pre-cooling the house before the peak starts. Moving 10% of the use in each day’s most expensive hours to its cheapest hours made time-of-use cheaper at 62 of 76 utilities; moving 20% at 68. Air conditioning in a hot afternoon is usually the biggest peak load and the hardest to move; pre-cooling helps, but only up to a point.
With an electric car
An EV changes the arithmetic, because it is a large load that can wait. Adding 1,000 miles a month in a Tesla Model Y Long Range AWD (275 kWh), charged at each plan’s cheapest start hour, time-of-use came out ahead at 72 of 76 utilities; at the median utility the household paid $119 less a year on it. Many utilities also sell a dedicated EV plan with a deeper overnight price; those are compared in EV rate plans compared.
How to decide for your own home
The typical home is an average, and few homes are average. Two things move the result more than anything else: how much of your use falls in the peak window, and how much of it you could move. A household that is out at work all day and runs its big loads at night is closer to the time-of-use winners above; one with someone home all afternoon in a hot climate is closer to the losers.
- Find your peak window. Each utility page lists every period of its plans; the off-peak hours table shows the peak and cheapest hours of every time-of-use plan side by side.
- Look at your own hourly data. Most utilities let you download a year of hourly or 15-minute use from their website (often labeled “Green Button”). The share of your kWh that falls in the peak window is the number that decides this.
- Run the comparison on your plans. The rate plan comparator prices every plan of your utility for your monthly use, with or without an EV, and shows which one comes out cheapest.
- Check the exit rules. Some utilities hold you on a new plan for a minimum period, and some offer bill protection in the first year: if time-of-use costs more than the old plan would have, they refund the difference. Your utility’s tariff page says which applies.
What this comparison leaves out: sales taxes and local fees, which scale with the bill on either plan; low-income and medical discounts; and critical-peak event days, which some time-of-use plans add on top of the regular periods. The methodology describes the engine in full.