Understanding a summer electric bill in Phoenix
A summer bill is two numbers multiplied together (the kilowatt-hours the house used and what each one cost) and the Phoenix climate loads the first of them heavily.
Short answer
A residential electric bill is mostly the number of kilowatt-hours the house used multiplied by a price per kilowatt-hour, with a fixed charge and often a time-of-day split on top. In Phoenix the usage half behaves the way the climate does, and the normal year carries 30.8 days at or above 100 °F in July against none at all in December.
A residential electric bill looks like one number and is actually two. The first is how many kilowatt-hours the house used. The second is what each of those kilowatt-hours cost. Everything else on the page (the fixed charge, the taxes, the adjustments, the meter read dates) sits around the outside of that multiplication.
Both halves move in a Phoenix summer, but they move for different reasons. The usage half moves because the climate does: a house here runs its cooling equipment for far more hours in July than in April, and no other appliance in a typical home comes close to that load. The price half moves because of a decision the household made at some point about which plan to be on, and because of the rules that plan carries, rules the utility publishes and this site does not reproduce.
The usage half, and why it is shaped like July
Normal days at or above 90 °F and 100 °F, by month
Each bar is the normal number of days in the month whose high reaches 90 °F. The figure under each month is the normal count of days at or above 100 °F, which is a smaller and much more concentrated number.
Normal day counts, NOAA NCEI U.S. Climate Normals 1991–2020, monthly summaries, Phoenix Sky Harbor (USW00023183). January, February and December have no bars because their normal count of days at or above 90 °F is zero; the 0 under those months is the same file's 100 °F count. The day counts are published values, not this site's arithmetic. The annual figure of 111.3 days at or above 100 °F is from the same dataset's annual summary.
The chart is a picture of a cooling season that does not taper. The normal count of days at or above 90 °F goes 2.1 in March, 10.2 in April, 23.6 in May, 30.8 in July, and is still 28.4 in September before it collapses to 16.8 in October and 1.4 in November. Phoenix does not have a hot fortnight in the middle of a mild summer; it has five months of near-ceiling loading with a hotter core inside it.
The 100 °F column is the more useful one for a bill, because it is the point at which cooling equipment stops being able to keep up cheaply. The normal count is 24.6 days in June, 28.5 in July, 27.1 in August and 18.2 in September: over a season, 111.3 days a year at or above 100 °F. On those days the equipment runs longer per hour of the day and more of the night, and the overnight run is the part that catches people out, because July’s normal low is 84.5 °F. A house that cannot open up at night runs its compressor at three in the morning, and that is a load no temperate city’s summer produces.
The price half
The second multiplication is smaller in arithmetic and larger in variation, and it is where most of the confusion lives. Four things can change what a kilowatt-hour costs.
A fixed charge is not a price per kilowatt-hour at all. It is a flat amount for being connected, and it is on the bill in January exactly as it is in July. It does not change with the season, and it does not change with the thermostat.
A single energy price is the simplest arrangement: every kilowatt-hour costs the same, and the bill is that price multiplied by the total on the meter.
A time-of-use split prices the same kilowatt-hour differently depending on the hour in which it was used. Both of the large Valley utilities publish options of this kind, and both publish the hours and the seasons that apply to each option on their own plan pages. This site does not reproduce those windows, because they differ between the two utilities, between plans at the same utility, and between summer and winter, and because a window quoted here could be out of date in a way the reader has no way to see.
A demand charge is priced on the highest sustained draw the household reached during the month, measured over a short interval rather than over the whole month. It is not a charge for energy at all; it is a charge for the peak rate at which energy was taken. A month can use the same total kilowatt-hours as the month before and cost more because of fifteen minutes inside it.
Which of these applies is a property of the plan, not of the climate, and it is written on the utility’s own page. The Peak-Hours Habit Planner is built to lay a household’s daily routine against a peak window so a reader can see which habits fall inside one: it does not tell anyone what to move.
What this page will not print
This page gives no rates, no window times, no monthly charges and no estimate of any reader’s bill. That is not caution for its own sake. A rate printed here would be wrong for most readers the day it was printed, and a bill estimate would be a guess dressed as a figure, which is the one thing this site does not do.
What is published, and what can be quoted honestly, is the state-level average. The U.S. Energy Information Administration’s Arizona profile puts the average retail price of electricity across all sectors in Arizona at 12.74 cents per kilowatt-hour for 2024. That figure is an average of every customer class in the state (residential, commercial and industrial together) so it is not a residential rate and it is not a price any household pays. It is useful for one thing only: showing that a bill is a usage number and a price number, and that both of them exist.
Why two identical houses get different bills
Two houses with the same floor plan, built the same year, on the same street, with the same number of people in them, can produce two very different summer bills. None of the differences below is a recommendation; they are the terms in the arithmetic.
| What differs | What it changes |
|---|---|
| Which plan the household is on | Whether the price per kilowatt-hour is flat, split by time of day, or partly charged on the month’s highest sustained draw |
| The kind of cooling equipment | A refrigerated system and an evaporative cooler draw very different amounts, and they behave differently as the humidity changes |
| The condition of the equipment | A filter that has not been changed, a coil that has not been cleaned and a system low on charge all make the same house work harder for the same indoor temperature |
| The thermostat setting and schedule | How many hours the equipment runs, which is the largest single term in the usage total |
| The building itself | Insulation, the attic, the windows, the age of the house and the direction it faces all set how fast heat gets back in |
| Shade and landscaping | Afternoon shade on west-facing glass and walls reduces the load during the hottest hours |
| A pool | A pump and, in most Valley pools, other equipment run on a schedule that the household chooses |
| Whether there is rooftop solar | Changes which kilowatt-hours are bought and which are taken from the array, and how the plan treats both |
| The meter read dates | A billing period with 33 days in it is not the same as one with 28, and a period that straddles a hot spell can look like a spike |
How to read your own bill
Every residential electric bill is assembled from a short list of parts. Not every plan uses every one of them, but these are the terms to look for on the page, and finding them takes a few minutes.
- The billing period, in dates and in days.
- The meter readings at each end, and whether they were actual or estimated.
- The total kilowatt-hours for the period.
- The fixed charge, if the plan has one, which appears whether or not anything was used.
- The energy charges, itemised by season or by time of day if the plan splits them.
- Any demand or capacity charge, with the interval it was measured over.
- Taxes, fees and the utility’s own adjustment items.
A bill that shows 31 days and a bill that shows 33 days are not comparable, and a period that contains a fortnight of the 28.5 days at or above 100 °F a normal July carries is not comparable with one that does not. Comparing this period against that one, on the same plan, is the honest comparison available without advice from anyone else.
Where the tools fit
Two tools on this site work on this problem from different ends. The Peak-Hours Habit Planner takes a household routine and shows which parts of it land in the hours a time-of-use plan prices differently, with links out to each utility’s own current plan pages rather than a stored copy of them. The Home Cooling Task Scheduler is the seasonal one: filter, coil, pad and service dates for the equipment that carries the summer, which is the part of the bill a household controls without changing anything about how it lives.
If the question is what the hours themselves look like across a day, On-peak hours and what to move takes that part, and Keeping a house cool at 115 degrees takes the building.
- NOAA National Centers for Environmental Information: U.S. Climate Normals 1991–2020, monthly summaries, Phoenix Sky Harbor (USW00023183)
Every day count and temperature on this page, the normal days at or above 90 °F and at or above 100 °F by month, and the normal highs and lows.
- U.S. Energy Information Administration: Arizona Electricity Profile
The average retail price of electricity across all sectors in Arizona, 12.74 cents per kilowatt-hour for 2024, and the fact that the figure is an all-sector average rather than a residential rate.
- Arizona Public Service: residential service and pricing pages
That more than one residential pricing option exists and that a kilowatt-hour is priced differently at different hours on some of them. No APS rate, window or charge is reproduced on this page.
- Salt River Project: residential price plan pages
The same two facts as above for the other large Valley utility, including that its price plans are set out in its own filed schedules. No SRP rate, window or charge is reproduced on this page.