Solar Panel ROI Calculator
Estimate how long a solar system takes to pay for itself and what it saves over 25 years — from numbers you already have: your electric bill and an installer quote.
Your numbers
How this calculator works
The math behind solar payback is simple in structure and slippery in the details. The structure: your net cost is the installed price minus incentives, and your payback period is how many years of avoided electric bills it takes to recover that net cost. The slippery part is that "avoided electric bills" isn't a fixed number — it grows as utility rates rise and shrinks slightly as panels age.
This calculator models both effects year by year for 25 years, the typical panel warranty period:
- Year-one savings = monthly bill × 12 × the share of your usage the system offsets.
- Each following year, savings are multiplied by (1 + electricity inflation) and by (1 − degradation).
- The payback period is the point where cumulative savings cross your net cost, interpolated to the month.
Worked example
Say you're quoted $20,000 for a system, a 30% tax credit applies, your bill averages $180/month, and the system is designed to cover 90% of your usage. Net cost is $20,000 × 0.70 = $14,000. Year-one savings are $180 × 12 × 0.90 = $1,944. Naively that's 14,000 ÷ 1,944 ≈ 7.2 years — but with 3% annual rate increases, savings grow each year and the crossover actually arrives around 6.7 years. Over 25 years, cumulative savings run well past $70,000 against the $14,000 outlay.
Now change one assumption: no tax credit. Net cost jumps to $20,000, and payback stretches to roughly 9.5 years. Still positive — but this is why you should never accept a payback figure without knowing which incentives it assumes. Our article on whether solar is worth it in 2026 covers how the incentive landscape affects the decision.
What this calculator leaves out (on purpose)
To stay honest about being an estimate, a few real-world factors are excluded rather than guessed at. Financing: if you take a solar loan, interest costs push payback out — often by 2–4 years. Inverter replacement: string inverters typically need replacing once, around year 10–15, at $1,500–$3,000. Net metering policy: if your utility credits exported power at less than the retail rate, your effective offset is lower than the design offset — ask your installer for the number under your utility's actual tariff, and use that here. Home value: studies generally find owned systems add resale value, but the effect varies too much by market to model responsibly.
Questions people ask
Is a 7-year payback good?
For a 25-year asset, yes. It implies roughly a 10%+ annual return on the net cost, tax-free (avoided spending isn't taxed). Under 6 years is excellent; over 12, the case gets thin and depends on you staying in the home.
What if I move before payback?
You don't lose everything — an owned system typically adds some resale value. But leased systems and loan balances complicate sales, which is one reason cash or short-loan purchases score better than 25-year financing.
Should I wait for panel prices to fall?
Panel hardware is now a minority of system cost; labor, permitting, and sales overhead dominate and fall slowly. Meanwhile every year you wait costs a year of savings. If the numbers work today, waiting rarely improves them; see how to estimate your payback before talking to a salesperson.