About WattMath
WattMath exists because most residential energy calculators are either broken, full of sales pitches, or built to capture leads rather than give you real answers.
We're building a suite of free, accurate, ZIP-code-aware tools for the five biggest residential energy decisions homeowners face: solar panels, electric vehicles, heat pumps, EV charging, and home battery backup. Our goal is simple — give you the same quality of analysis that a well-informed engineer friend would give you, for free, without a sales call.
How we build our calculators
Every calculator on WattMath uses authoritative public data:
- Solar production — NREL PVWatts API, the same tool used by installers, utilities, and the U.S. Department of Energy.
- Electricity rates — U.S. Energy Information Administration (EIA) monthly residential data, cached and refreshed automatically.
- Federal incentives — IRS publications for the 30% solar ITC, 25C heat pump credit, and 30D EV credit.
- State and local incentives — hand-verified quarterly from DSIRE and utility program pages, with last-verified dates shown in results.
We publish our methodology for each calculator so you can check our math. We never determine tax credit eligibility — that requires a tax professional — but we make sure you know what credits exist and where to learn more.
What we're not
WattMath is not a solar installer, EV dealer, or financial advisor. We don't sell leads. We don't have a preferred installer to refer you to. We earn revenue through display advertising and transparent affiliate partnerships (e.g., EnergySage for solar quotes, Amazon for EV accessories), disclosed on any page where they appear.
Get in touch
Found an error in our math? Have a calculator suggestion? Email us at hello@wattmath.com. We read everything.