These are estimates, not bills
Every calculator on this site produces an estimate. It uses the figures you enter and, where you do not supply one, a published average. Your real bill is determined by your utility's tariff, which is a legal document running to dozens of pages and containing provisions no general-purpose calculator can model.
Among the things that routinely make a real bill differ from an estimate: tiered rate blocks that change the price per kilowatt-hour once you pass a threshold; time-of-use rates that price the same kilowatt-hour differently by hour and season; minimum-usage fees that penalise low consumption; fuel and purchased-power adjustment clauses that move monthly; demand charges; franchise fees and gross receipts taxes that vary by municipality; and billing periods that are not thirty days long.
Why an estimate and a bill diverge in practice
Three mechanisms account for most of the gap, and none of them means anything is wrong.
The billing period is not a month. Meter reading routes run on a working-day cycle, so a period lands near a month but rarely on thirty days. A period a few days longer than the last one carries a few days more consumption, and if the rate is tiered those extra days are billed in the highest tier you reached. Comparing two bills without first comparing their period lengths is the single most common way people convince themselves a rate has risen when it has not.
The read may be estimated rather than actual. When a meter cannot be read — access, weather, a route missed — the utility bills an estimate based on your history and then trues it up at the next actual read. The estimated bill looks unremarkable; the true-up bill that follows contains the difference and can look alarming. Bills normally mark which kind of read they used, often with a single letter or word next to the reading.
A rate change mid-cycle is prorated. When a tariff, a rider or a fuel adjustment changes partway through your billing period, the utility splits the period and bills each part at the rate in force. The result is a bill that matches neither the old rate nor the new one, and it will not match a calculator that applied a single rate to the whole period. Seasonal rate definitions do the same thing on a fixed calendar date.
Where our figures come from
State electricity rates and consumption come from the U.S. Energy Information Administration. The period each figure covers is printed on the page. Appliance wattages and runtimes come from the U.S. Department of Energy, the EIA Residential Energy Consumption Survey, ENERGY STAR product criteria, and published utility engineering tables. Where sources disagree materially we say so on the page rather than silently picking one.
Appliance figures in particular
Appliance numbers deserve a specific warning: the three kinds of figure in circulation measure different things and are routinely quoted as if they were interchangeable.
- A nameplate rating is the manufacturer's stated maximum electrical draw. It describes what the appliance pulls at full load, not what it averages. A device that cycles, modulates, or spends most of its time idle will consume a fraction of it.
- An EnergyGuide label gives estimated annual consumption under a standardised test procedure, designed so two models can be compared fairly. The test conditions are fixed and are not your house, your climate, your thermostat setting or your habits.
- Metered survey data, such as the figures behind the EIA Residential Energy Consumption Survey, describes what appliances in real homes actually used, averaged across a population containing new and twenty-year-old units alike.
For the same nominal appliance these three can differ by a factor of three. That is not an error in any of them; it is three different questions with three different answers. Our appliance calculator and the appliance pages state which kind of figure is used, and where sources conflict materially the page says so.
Averages describe populations, not households
A state average is the arithmetic result of dividing total residential revenue by total residential customers. No individual household is average. A 900-square-foot apartment with gas heat and a 3,000-square-foot house with a heat pump both sit inside the same state figure and neither resembles it. Use the average as a reference point, not a target.
If you think your bill is wrong
Work through this in order. Most bills that look wrong are explained by the first three steps, and arriving at the fourth with answers in hand makes the call shorter.
- Check the period length. Find the service dates on the bill and count the days, then do the same for the bill you are comparing it with. Divide the total by the days to get a cost per day, the only fair comparison between periods of different length.
- Check whether the read was estimated. If this bill is a true-up after one or more estimated reads, the charge covers consumption that was under-billed earlier rather than a sudden increase in usage.
- Compare against the same month last year, not last month. Utility consumption is seasonal. January against December tells you about the weather; January against last January tells you about your house. If usage and period both look normal and only the cost moved, a rate or a rider changed.
- Then contact the utility. Ask them to confirm the read type, walk the charges line by line, and say which tariff and riders applied. Ask for a re-read or a meter test if the usage looks impossible. Note the date, the name and the reference number.
- Then escalate to your state public utility commission. If the utility's explanation does not hold up, the commission holds the approved tariff, regulates the utility, and runs a formal complaint process the utility must answer. It is free.
The guide to why a bill goes up covers the first three steps in more detail.
Not professional advice
Nothing here is financial, legal, tax, or engineering advice. We are not your utility and we have no relationship with it. If you are disputing a bill, facing disconnection, or deciding between supply contracts, talk to your utility, your state public utility commission, or a qualified professional.
No supplier relationships
We take no payment from energy suppliers, brokers, marketers, or comparison services, and we do not receive commissions on enrolments. Where a page describes how to shop for supply in a deregulated market, it is describing the mechanics, not recommending a company.
Corrections
If something here is wrong, tell us through the contact page and we will correct it.