What are time-of-use electricity rates?
Why the same kilowatt-hour can cost three times more at 6pm than at 2am, how to tell whether you are on such a plan, and what actually changes if you are.
Reviewed
One rate, or several
Most US households are on a flat rate: every kilowatt-hour costs the same whenever it is used. Every figure on this site assumes that, which is why each page says it excludes time-of-use pricing.
A growing number of utilities instead charge by the hour. The same kilowatt-hour might cost 12 cents overnight and 35 cents on a summer weekday afternoon. Nothing about your appliance changes; only the price attached to the moment you run it.
The reason is supply. Late afternoon is when demand peaks and the most expensive generation is brought online, so utilities pass that cost through in the hope of shifting demand away from it.
How to tell whether you are on one
Look at your bill for more than one price per kilowatt-hour. Plans list them as peak, off-peak and sometimes mid-peak or super-off-peak, each with the hours they apply.
If your bill shows a single rate and a single usage figure, you are on a flat plan and the estimates on this site apply directly.
Some utilities enrol new customers on time-of-use by default, particularly in California and parts of the southwest, so it is worth checking rather than assuming.
What actually changes
Only appliances whose timing you control are worth moving. A dishwasher, a clothes dryer, a pool pump and an electric vehicle can all run at 2am with no loss of function.
A refrigerator cannot be shifted, and neither can lighting or cooking. Trying to move them produces inconvenience rather than saving.
The largest single opportunity for most households is vehicle charging, because it is a large load, entirely schedulable, and most cars can be told to start at a given hour.
Whether it is worth switching
Time-of-use only pays if your usage genuinely moves. A household that runs the air conditioning hard from 4pm to 8pm will pay more on a time-of-use plan than a flat one, not less.
The honest test is your own daily pattern. If most of your consumption is already outside peak hours, or you can shift it without irritation, the saving is real. If not, a flat rate is the safer choice.
Utilities generally publish both tariffs. Multiplying your own hourly usage against each is the only reliable comparison, and your utility can usually supply that hourly data on request.