Free Energy Calculators
for Homeowners
Accurate, ZIP-code-aware tools for every major residential energy decision — solar, EVs, heat pumps, and home batteries. No sales pitch. Just the numbers.
All Calculators
Each calculator uses real data from NREL, EIA, and IRS guidelines.
Solar Payback Calculator
Find out how long until solar panels pay for themselves. Enter your ZIP code and electric bill for a personalized estimate.
Calculate solar payback →EV vs. Gas Cost Calculator
Compare the true total cost of ownership between an electric vehicle and a comparable gas car over your ownership period.
Compare EV vs. gas →Heat Pump vs. Furnace ROI
See if a heat pump makes financial sense for your home. Includes the federal 25C tax credit and utility rebates.
Calculate heat pump ROI →EV Charging Cost Calculator
Calculate what it actually costs to charge your EV at home or on the road, and compare to the equivalent gas cost.
Calculate charging cost →Home Battery Sizing Calculator
Size a home battery backup for your critical loads. See which Powerwall or Enphase configuration fits your needs.
Size my battery →Why trust WattMath?
Solar production estimates powered by NREL PVWatts, the same tool used by installers and utilities.
Electricity and gas prices sourced from the U.S. Energy Information Administration, updated monthly.
All calculators are free and anonymous. No account required, no personal data collected.