When is electricity most expensive? It depends on your utility

On a time-of-use tariff, the same kilowatt-hour costs a different amount depending on when you use it. Advice about these tariffs tends to quote one window, usually 4 to 9 pm, as if every utility used it. In the filings, almost nothing about the peak is standard: not when it starts, not how long it lasts, not how much more it costs.

No two utilities agree

We looked at 95 utilities with current residential tariffs whose price changes by the hour, and at the hours each one charges its highest price on a summer weekday. Between them they use 49 different peak windows. The most common is shared by only 10 utilities:

Summer weekday peak	Utilities using it
2 pm to 7 pm	10
3 pm to 7 pm	8
4 pm to 8 pm	7
5 pm to 9 pm	7
1 pm to 7 pm	6
4 pm to 9 pm	6

The 4-to-9 window gets quoted partly because California's large utilities use it, and they file a great many tariffs: Pacific Gas & Electric alone has 22 time-of-use filings, one for each tariff and climate region. Counted tariff by tariff, 4 to 9 pm comes first. Counted by utility, it is one window among many.

The one hour nearly everyone agrees on is 5 to 6 pm. At 81 of the 95 utilities, every time-of-use tariff they file charges peak prices then.

How long the peak lasts

The typical peak lasts five hours. At 32 utilities it is four hours or less; at 27 it is eight or more.

• Shortest: three hours, at Austin Energy and Duke Energy Carolinas, among others.
• Longest: twelve to fourteen hours at Consolidated Edison, Kentucky Power and Rochester Gas & Electric, where the peak covers most of the waking day. Middle Tennessee EMC's Niteflex rate charges its peak price from 4 am to 10 pm and keeps the cheap hours for the night.

Length matters more than it sounds. A three-hour peak can be avoided by running the dishwasher and the dryer a little later. A fourteen-hour one cannot be avoided by anyone who is home during the day.

How much more the peak costs

At the typical utility, the peak price is 2.6 times the price of the cheapest hour on the same summer weekday. At 34 utilities it is three times or more; at 68, at least double.

In winter the gap narrows, to a typical 2.2 times.

Weekends and winter are different

• Weekends are usually free of the peak. At 64 of the 95 utilities, no time-of-use tariff charges peak prices on a summer weekend.
• The hours move with the season. 87 of the 95 also price by time of day in January, and at 45 the peak hours in winter are not the summer ones.
• Winter often adds a morning peak. At 49 utilities a winter weekday peak includes time between 6 and 9 am, when heating comes on. At 23 of them the winter day has two separate peaks, morning and evening.
• Some peaks are summer only. 8 utilities price by time of day in summer and charge one price around the clock in winter.

How we measured this

• Current tariffs: filed since 2020, priceable from usage alone, priced as a whole home's bill, open to any household and not flagged as a likely data error, the same set this site ranks.
• Time-of-use: tariffs whose weekday price changes by at least 2% with the hour of the day. Tariffs whose price changes only with the season are left out.
• The peak: the hours charged the highest energy price on a July weekday, or a January one for winter. A shoulder or mid-peak period counts as off-peak here, so the windows are the most expensive hours, not every hour above the cheapest.
• Counted by utility: many utilities file several time-of-use tariffs, and counting tariffs lets a handful of them decide the result. A utility whose tariffs use different windows counts once for each.
• Prices per kWh, including the adjustments each filing lists, before fixed charges.

What to do with this

• Find your own window. It is printed on your tariff sheet and usually on your bill. Do not assume it is 4 to 9 pm.
• Check it for the season you use most. A peak you can live with in winter may be a different, longer one in summer.
• Then decide whether time-of-use suits you. How to read a time-of-use tariff walks through what to look for, and is time-of-use cheaper? shows how often it saves money for a household that changes nothing.

The calculator prices every current tariff your utility files across a whole year at your usage, time-of-use options included, so you can compare them before you call to switch.