How we calculate
Cost of a plan = your energy use in each hour × that hour's price, plus the plan's monthly charges. If the time-of-use plan costs less than the flat plan, you save.
Energy use by hour: when homes use electricity
On a time-of-use plan, what you pay depends on when you use the power. The National Laboratory of the Rockies (formerly NREL, the National Renewable Energy Laboratory) publishes ResStock, an open-source model of home energy use. It gives the average home's use by appliance type, by hour and by state. We use it in the estimate, and you can explore it here:
Less use More use Most use The color shows how much of the day's use falls in that hour, not the price.
Source: NREL ResStock (2025 release 1, 2018 weather), existing homes, weekdays. Each bar is that hour's share of the day; the bars add up to 100%.
Rates: the cost of energy
A flat-rate plan charges the same price for electricity at all times of day, for example $0.196 per kWh (the dashed line below).
A time-of-use plan charges by a “rate schedule”: a different price for each hour of the day, and often different prices on weekdays and weekends, and in summer and winter.
Most utilities publish their rates on their website or in “tariff” PDFs. For about 98% of the people in our data who can get a time-of-use plan, the rates come from the utility's own documents, which we link to. For the rest (139 of 349 utilities, mostly small ones), we use the Utility Rate Database (URDB).
Savings
From the energy model for your state and the appliances you choose, we estimate your use in kWh for each hour of a typical weekday and weekend day, month by month. We price that use on the best available time-of-use plan* where you live, and again on your utility's standard flat plan. The difference is what you could save, or the extra cost, if you switch to time-of-use.
*Best available plan: of the plans sold where you live, the one that costs your home the least. We leave out plans that need something we do not ask about, such as solar panels, a battery, a special meter, or a farm. Plans for homes with an EV, a heat pump, electric heat or an apartment count when your answers say your home has one. EV plans are in on purpose: EV drivers are the people most likely to save.
More details
How a plan's prices become your bill
Hours. Each hour of your use is priced at the plan's price for that hour, season and day of the week. The flat plan prices every hour the same.
Tiers. Some plans charge more per kWh after a monthly amount. We price these at your average month, so a home with a very high winter and a low summer is only approximate.
Demand charges. Some plans also charge for your highest use (kW) in a window. We do not know your peak, so we assume 10 kW, and the plan card says so. An all-electric home can peak higher, which costs more.
Event days. Some plans charge a high price on days the utility calls an event. We assume every allowed event day is called, with your usual use in the event hours.
Your bill. If you enter one month's bill, we compare it with what we expected your home to use that month. Each part of your use (lights and appliances, cooling, heating, hot water, EV charging) takes a share of the difference: a larger share when it is a big part of that month, and when our estimate of it is less certain. Cooling and heating are the least certain. So a July bill mostly changes cooling, and a January bill mostly changes heating. Your EV takes a share too, because monthly miles and kWh per mile are hard to know exactly. Each part is then scaled for the whole year. A bill in dollars is read at your utility's flat price, so use dollars only from a flat-rate bill; kWh works from any bill. A bill under half or over twice a typical home's use is not used: a wrong answer (for example, electric heat entered as gas) is more likely, and solar panels, batteries or a pool change use in ways we do not model yet.
Notes.
- An average home. Everything is set to the average from the statistics. No one is exactly average, so your home will not be modeled exactly right.
- Your EV. If you have an EV, we assume you charge it at home in each day's cheapest hours, usually overnight.
- No other changes. We do not assume that you change anything else: for example, cool your home before the peak, put your water heater on a timer, move laundry or dishwashing to cheaper hours, or are at home more or less than a typical household. Each of these can save more, so your real saving can be larger than our estimate.
- Mistakes. Getting every rate schedule in the country into one form, and matching each to the places it serves, is not easy. There will be mistakes. Report them! Take it easy on me.
Heat pumps in cold states
Heat-pump use comes from NREL ResStock, which models the heat pumps in homes today. In cold states these are mostly standard units that switch to electric-resistance backup in deep cold (in Minnesota every modeled heat pump is a standard unit). A new cold-climate heat pump can use much less, so if you have one, enter a bill: the estimate then scales to your real use.