A utility bill is the single best source of truth for almost every input RetrofitROI's engines ask for, more reliable than a contractor's estimate and far more reliable than a remembered impression of what you "usually" pay. Reading it correctly takes a few extra minutes and changes how trustworthy your results are.
Find your actual rate, not your bill total
Your bill total includes fixed charges, delivery fees, and taxes on top of the per-unit energy rate. For a rate figure, divide the energy line item specifically, not the grand total, by the kWh or therms used that period. The utility bill cost decomposition engine is built specifically to split a real bill into its component charges if the layout is confusing.
Use a 12-month total, not one month
Energy use swings with the seasons: heating load in winter, cooling load in summer. A single month's bill, divided by usage, gives you that month's rate and cost but not a representative annual figure. Pull 12 consecutive months if your utility's portal offers a usage history, sum the totals, and use that for any engine asking for an annual cost, like the annual energy cost forecast engine.
Separate the fuels if you have both
A gas-and-electric household needs both bills read separately for a fuel-switching decision. Mixing a blended cost per unit across two different fuel types produces a meaningless number; RetrofitROI's fuel-switch engines, like the heating fuel switch breakeven engine, always ask for each fuel's rate on its own.
What a bill cannot tell you
A bill tells you what you paid, not what a specific new piece of equipment would cost to run. It cannot isolate how much of your bill is water heating versus space heating versus everything else without more work, which is exactly the gap the hot water energy cost engine is built to close using a smaller set of assumptions about your household.
Time-of-use and demand bills need a different read
If your utility bills you on a time-of-use or demand-charge structure, a single blended rate understates the real picture. You need the peak, off-peak, and (if applicable) demand rates separately, usually shown as separate line items or a rate schedule reference on the bill. The time-of-use versus flat rate engine and the demand charge bill impact engine both need this level of detail to be useful.
Watch for a rate change mid-year
Utilities revise rates periodically, sometimes seasonally. If your 12-month history spans a rate change, your averaged historical rate may understate what you will actually pay going forward. Where possible, use your most recent bill's rate for forward-looking calculations and your full-year total only for usage volume.
Solar-specific bill reading
If you already have solar, your bill likely shows net usage after your system's production, not your home's raw consumption. For the solar export credit value engine and similar tools, you need your export credit rate specifically, usually listed separately from your import rate, not the net dollar figure on the bill's summary line.
Frequently asked questions
My bill only shows a total dollar amount. Where do I find kWh or therms?
Most utilities show usage in a "usage history" or "your energy use" section, often as a bar chart with a table underneath, sometimes on a separate page or in the online account portal rather than the printed summary page.
One month looked unusually high. Should I use that month?
No, use a full 12-month total or a representative average unless you are specifically modeling a seasonal decision like solar production or heating-season cost. A single unusual month, from a heat wave or a house guest, will skew every downstream calculation.
What if my rate has multiple tiers or blocks?
Use your blended average rate, total dollars spent on energy divided by total units used, for most RetrofitROI engines. A few tools, like the time-of-use comparison, ask for tier-specific rates directly because the structure itself is what is being compared.