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Price your usage across the day
A time-of-use tariff prices the same kilowatt-hour differently by hour and season. Whether it beats a flat rate depends entirely on when you use electricity, not how much — which is why the honest answer for some households is no.
Cost on this time-of-use plan
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Enter your usage in each period.
What time-of-use pricing is, and why the windows sit where they do
A time-of-use tariff charges a different price for the same kilowatt-hour depending on the hour it was consumed. The day is cut into two, three or occasionally four named periods — on-peak, mid-peak, off-peak, super off-peak — and an interval meter records how much you used in each.
The windows are drawn around the system peak: the hours when demand across the grid is highest and the utility is running its most expensive generation. They are not drawn around customer convenience, and no utility will move one to suit a household.
That is why most residential peak windows now sit in the late afternoon and early evening rather than at midday. Solar generation moved the problem. Where rooftop and utility-scale solar are abundant, midday has become the cheapest part of the day, and the expensive hours begin when the sun drops and demand does not. Hawaiian Electric's residential time-of-use schedule is the clearest example: three fixed windows all year, with the daytime window the cheapest and the early-evening window by far the dearest. If you assumed midday was expensive, that plan is shaped against your intuition; the guide to time-of-use rates explains why.
Finding your own usage by period
This is the hard part, and where most comparisons go wrong. The calculator needs kilowatt-hours split by period; a flat-rate bill gives one total. Three sources, best first:
- An interval usage download from your utility. Most utilities with smart meters publish hourly or fifteen-minute data in the online account portal, often as a CSV export under the Green Button standard. Download a summer month and a winter month, then add up the hours inside each proposed window.
- The utility's own usage charts. Portals that will not export raw data often still chart consumption by hour of day — crude, but usable.
- A meter display or home energy monitor. Some smart meters report by period directly; a whole-home monitor does it continuously.
Otherwise, estimate honestly. The naive method — dividing the monthly total by the share of hours the peak window covers — understates peak usage for almost every household, because the evening peak is when people are home, cooking, running laundry, and cooling a house that heated up all day. Treat the hours-share figure as a floor, then add for every load you know runs then. To check the total you are splitting, work backwards from the meter with the electricity bill calculator.
Who wins, and who loses
A calculator that only ever says yes is not a calculator. Time-of-use pricing pays some households well and costs others real money.
Usually better off:
- Electric vehicle owners who charge overnight. Typically the largest flexible load a household has, running in the cheapest hours by default.
- Households that can genuinely move laundry, dishwashing and pool pumps out of the peak window — every week, not once.
- Homes with battery storage, which charge cheap and discharge through the peak automatically.
- Homes empty on weekday afternoons, where the peak covers hours nobody is there.
Usually worse off:
- A household at home all day in summer with central air conditioning. The peak falls when the house is hottest and fullest, and cooling cannot be postponed to midnight.
- Anyone with high peak-hour usage and no concrete plan to change it. Intending to shift is not shifting.
Run it twice: on your usage as it is, and on the usage you would have if you did everything you intend to. If it wins only in the second run, you are betting on a change you have not made. For some households the right answer is to stay on the flat rate.
The seasonal trap
Many utilities change two things between summer and winter: the price of each period, and the hours it covers. A decision made on winter numbers can reverse in July, because summer is when the peak price does its real work.
Three shapes are common enough to name.
- Same window, different prices. Several California residential plans hold a fixed late-afternoon and early-evening peak all year and move only the prices, the summer peak well above the winter one.
- Different window and different prices. One large Arizona utility replaces a single long summer afternoon peak with two shorter morning and evening peaks in winter, and splits the year into three seasons rather than two. Another adds a cheap midday winter block that does not exist in summer.
- A peak in one season only. A Georgia plan has no winter on-peak period at all, so every hour from October through May is off-peak. A northern Nevada plan is flat all winter, with a short summer evening peak. On plans like these a winter comparison is meaningless: winter is the easy half.
Treat the season toggle as a requirement, not an option: run summer first, then winter, then weigh the two by how many months each covers.
You may already be on one without choosing it
Time-of-use began as an opt-in for enthusiasts. In a growing number of territories it is now the standard residential rate, so a household can be on one having never chosen it.
The picture is mixed, which is why this is worth checking:
- California's large investor-owned utilities have moved most residential customers onto default time-of-use plans, and one Sacramento municipal utility's standard residential rate is a time-of-day rate.
- Elsewhere the default is still flat or tiered. A New York utility's default residential rate is flat; a large Arizona public power provider defaults to a non-time-of-use plan; Georgia and Hawaii both default to tiered schedules.
Three ways to find out which you are on, quickest first. Read the rate schedule name on your bill: letters such as TOU or TOD, or a plan name containing a span of hours, are the giveaway. Read the energy charges: kilowatt-hours listed on more than one line under different period names mean a time-varying rate. Failing both, open your online account, where the plan is normally named up front. Being defaulted onto one is not a problem in itself; being on one unknowingly is, because the mechanism only pays if you know which hours to avoid.
What this tool does not model
The comparison here is deliberately simple: your kilowatt-hours by period at your prices, against the same usage on one flat rate. Five omissions can change it.
- Demand charges. A charge based on your highest rate of draw, in kilowatts rather than kilowatt-hours, so two households using the same total can pay differently. How to tell: a line priced in kW.
- Critical peak pricing and peak-event days. A handful of days a year when the peak price is multiplied, or a credit is paid for cutting back, announced a day ahead. These can dominate the arithmetic.
- Baseline credits. Some plans pair time-of-use periods with a per-kilowatt-hour credit inside a baseline allowance, so a light user's effective prices sit below published ones. The tiered electric rate calculator explains how allowances are set.
- A different fixed charge. The time-of-use plan and the flat plan it replaces do not always carry the same monthly customer charge.
- Weekend and holiday treatment. Some plans exempt weekend hours and listed holidays from the peak; others apply it every day of the year.
One further thing to confirm: several time-of-use plans require a minimum enrolment, commonly twelve months. If the plan proves wrong in the first heatwave, you may be unable to leave until the term is up.
Frequently asked questions
How do I find out how much electricity I use during peak hours?
Ask your utility for interval data. If you have a smart meter, the online account portal almost always offers hourly or fifteen-minute usage, often downloadable as a CSV and frequently under the Green Button standard. Export a full summer month and a full winter month, then sum the hours that fall inside each period of the plan you are considering. If raw data is not offered, many portals still chart usage by hour of day, which is cruder but workable. Without either, estimate by hours as a floor and add for the loads you know run in the evening — cooking, laundry, and air conditioning recovering a hot house.
Will a time-of-use plan save me money?
It depends entirely on when you use electricity, and for some households the honest answer is no. Overnight electric vehicle charging, movable laundry and dishwashing, and battery storage all push the result strongly toward yes. A household at home through summer afternoons with central air conditioning usually loses, because cooling cannot be postponed to midnight and the peak window is exactly when the house needs it. Run your real usage, not your intended usage, through the comparison first. If the plan wins only on the numbers you hope to achieve rather than the ones you have, treat that as a reason to wait.
How do I know if I am already on a time-of-use rate?
Check three places. First, the rate schedule name printed on the bill: letters such as TOU or TOD, or a plan name containing a span of hours, mean a time-varying rate. Second, the energy charges themselves: if your kilowatt-hours are listed on more than one line with different period names and different prices, the rate is time-varying. Third, your online account, which normally names the current plan on the first screen. This is worth checking rather than assuming, because in a growing number of territories time-of-use is now the default residential rate, so a household can be on one without ever having opted in.
Do weekends and holidays count as peak hours?
It varies by plan, and the difference is large enough to change a decision. Some residential plans treat all weekend hours and a listed set of holidays as off-peak year-round, so the peak window only ever applies Monday to Friday. Others apply the peak every day of the year, weekends and holidays included, with no exemption at all. A third pattern bills the same window at a cheaper mid-peak price at weekends rather than exempting it. Find the answer in the rate schedule before you estimate anything, because a household that does its flexible chores at weekends gets a very different result under each.