Solar simple-payback calculator

Assumptions and limits

Defaults use the US residential rate and monthly use from EIA (2025) and the national installed-price median from Berkeley Lab (systems installed in 2025, in 2025 dollars). The starting yield is the median PVGIS estimate across the 347 cities on this site (1470.2 kWh per kW per year). Replace it with your city's estimate. The starting bill is monthly use multiplied by the rate.

Annual use = monthly kWh × 12, or monthly bill divided by the dollar-per-kWh rate × 12. Size = annual use divided by yield. Gross cost = size × 1,000 × price per watt. Annual production = size × yield. Annual value = production × retail rate × [(1 − export share) + export share × export-credit fraction]. Simple payback = (gross cost − upfront incentives) divided by annual value.

The federal 25D credit ended for systems installed after Dec 31 2025. Incentives default to zero; enter only incentives you qualify for. This model sizes solar to annual use. It excludes batteries, financing, maintenance, degradation, rate escalation, discounting and time-of-use effects. Fixed bill charges may remain; bill mode can overestimate usage. State averages are not utility tariffs. Export rules and actual roof production vary. Calculations stay in your browser. Data sources.