Our Methodology

Data Sources

We pull data from official government and industry sources including the U.S. Energy Information Administration (EIA), the Environmental Protection Agency (EPA), the Department of Energy (DOE), and state utility commission rate filings. Fuel prices are updated regularly using EIA weekly averages. Electricity rates reflect current national and state-level averages.

Calculation Approach

Each calculator uses a total-cost-of-ownership (TCO) model that accounts for upfront costs, ongoing operating expenses, maintenance, financing costs, available incentives, and projected savings over the analysis period. We apply standard financial formulas for present value, loan amortization, and payback period calculations.

Assumptions & Defaults

All calculators pre-fill sensible default values based on national averages. Users can adjust every input to match their specific situation. Key assumptions (such as annual rate escalation, equipment degradation, and maintenance costs) are stated in each calculator’s methodology section.

Incentives & Tax Credits

Federal incentive data reflects the changes made by the July 2025 budget reconciliation law: the federal clean vehicle credits ended for vehicles acquired after September 30, 2025, and the residential clean energy (solar/battery) and energy efficient home improvement (heat pump) credits ended December 31, 2025. Our calculators default federal credits to zero and let users override them for grandfathered purchases. State-level incentives are governed separately, remain active in many states, and are sourced from the Database of State Incentives for Renewables & Efficiency (DSIRE). We update incentive data as legislation changes.

Limitations

Our calculators provide estimates based on the inputs you provide and general assumptions. Actual costs and savings will vary based on your specific location, usage patterns, equipment choices, installer pricing, and local regulations. Results should be used as a starting point for research, not as financial advice.

Per-Calculator Details

Each calculator page includes a detailed “How We Calculate This” section explaining the specific formulas, assumptions, and data sources used for that calculation. We encourage you to review these before making decisions.