Methodology and sources
Every number on this site comes from a public dataset. Here is which one, how we process it and which assumptions the calculators make. Data status: EIA-861 2025, monthly electricity prices through Aug 2026, natural gas 2025, heating oil and propane 2025/26 winter, retrieved 2026-11-05.
Utility rates and average bills
Source: U.S. Energy Information Administration, Form EIA-861 "Annual Electric Power Industry Report", file Sales to Ultimate Customers, data year 2025. Every utility and retail power marketer reports residential revenue, kWh sold and number of customers per state.
Calculation: average price = revenue ÷ kWh; average bill = revenue ÷ customers ÷ 12; average usage = kWh ÷ customers ÷ 12. Revenue includes fixed customer charges, riders, fuel adjustments and, in most cases, taxes collected on the bill. Full-service ("bundled") and delivery-only customers are shown separately. Values outside 3–80¢/kWh are treated as reporting errors and left out. Pages exist for utilities with at least 50,000 residential customers; smaller utilities appear in the state tables and the ZIP lookup.
State values: EIA-861 "Average Monthly Bill – Residential" table, which includes all utilities and retail providers.
Monthly prices
EIA Open Data API: electricity retail sales by state, residential sector (monthly); natural gas price delivered to residential consumers (annual, $/Mcf, converted at 10.37 therms per Mcf); heating oil and propane residential prices from the State Heating Oil and Propane Program (weekly during the heating season, averaged October–March). States without a survey use the U.S. average, marked as such.
ZIP code to utility
"U.S. Electric Utility Companies and Rates: Look-up by Zip Code (2024)", Open Energy Data Initiative (OEDI), National Renewable Energy Laboratory, licensed under CC BY 4.0. We use the ZIP-to-utility assignment and combine it with the 2025 figures above. ZIP codes in competitive areas of Texas are not assigned to a retail provider, because customers choose one.
Climate
NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, monthly average temperature and heating degree days (base 65 °F) for 7,284 stations. Each ZIP code (Census 2024 ZCTA center point) is matched to the nearest station with complete data. In mountain areas the nearest station can be at a different elevation than you.
Heat pump calculator
- Heating need from home size: 0.32 / 0.24 / 0.16 BTU/(h·ft²·°F) for drafty / average / well-insulated homes × 24 × heating degree days. These factors are rough and calibrated to typical gas use; the fuel-use method is more accurate.
- Heating need from fuel use: units × energy content (natural gas 100,000 BTU/therm, propane 91,452 BTU/gal, heating oil 138,500 BTU/gal, electricity 3412.14 BTU/kWh) × efficiency of the old system.
- Heat pump COP at 47 °F / 5 °F: Standard heat pump (HSPF2 ~7.5): 3 / 1.5; High-efficiency (HSPF2 ~8.5): 3.4 / 1.8; Cold-climate / variable speed (HSPF2 ~9.5+): 3.8 / 2.4. Linear in between, slightly rising above 47 °F, −10% for defrost between 17 and 45 °F, never below 1 (backup resistance heat).
- Seasonal COP: each month's COP is the harmonic mean of the COP at the monthly average temperature and 10 °F below it; months are weighted by heating degree days.
- Not included: equipment and installation cost (enter your own quote difference), cooling (a heat pump also replaces the air conditioner), and fixed gas customer charges you would save by disconnecting gas completely.
Water heater calculator
- Heat = gallons/day × 8.34 × (setpoint − inlet temperature) × 365. Default use: 15 + 11 gallons per person and day.
- Inlet water temperature ≈ annual average air temperature + 6 °F (Burch & Christensen, NREL).
- Efficiency (Uniform Energy Factor): Gas tank (standard) 0.64, Gas tankless (condensing) 0.93, Electric tank (resistance) 0.92, Heat pump water heater 3.3, Propane tank 0.62.
Corrections
Found a number that looks wrong for your utility? Write to contact@electricbillmath.com with your utility and, if you can, a recent bill total and kWh. We check every report against the source data.