Solar Panel Calculator: Panels, Cost and Payback for 2026
Going solar starts with three honest questions: how many panels your electricity use actually needs, what the system will cost at today’s prices, and how long it takes to pay for itself. This solar panel calculator answers all three from numbers you already have — your monthly usage in kilowatt-hours or the dollar amount of your bill, your electricity rate and the peak sun hours where you live. It sizes the system in kilowatts, counts the panels, and estimates the roof space, monthly and annual production, installed cost and payback. Every figure assumes no federal tax credit, for the reason explained next.
The 2026 tax credit change — read this first
The federal rules changed at the end of 2025, and many solar pages on the internet have not caught up. The residential clean energy credit — Section 25D of the tax code, worth 30% of the installed cost for years — ended on 31 December 2025. A system installed in 2026 does not qualify for it. That is why every figure on this page assumes no federal credit: the estimated cost is the full installed price at $3.00 per watt, before incentives.
Help may still exist closer to home. Some states, cities and utilities still offer rebates, tax exemptions or performance payments such as SRECs, which can cut the net cost meaningfully. They vary too much by address to build into a national calculator, so treat any state or local incentive you qualify for as a bonus on top of these numbers.
Solar Panel Calculator
Start from what you actually know — your monthly electricity use in kilowatt-hours, or the dollar amount of your monthly bill — then add your rate, your sun hours and a panel wattage. Results update as you type, or press Calculate.
Fixed assumption: a real-world efficiency factor of 0.8 is applied throughout, covering inverter, wiring, temperature and soiling losses. Installed cost is estimated at $3.00 per watt before any state or local incentives, with no federal tax credit included.
Enter your numbers, then press Calculate — the results update as you type.
Savings cannot exceed your bill — if your system produces more than you use, the extra is worth less unless your utility pays full net-metering rates.
How the calculator works
Start with a month of electricity. Dividing monthly usage by 30 gives an average day, and dividing that by your peak sun hours — reduced by the 0.8 efficiency factor — gives the system size in kilowatts that would cover it. In bill mode the calculator works backwards first: bill divided by rate gives the implied usage, so a $150 bill at $0.17/kWh means about 882 kWh. Panels are then rounded up to a whole number, because you cannot fit part of a panel, and every later figure is worked out from that actual, slightly larger system. Cost is the actual watts multiplied by $3.00, and payback is that cost divided by a year of monthly savings.
Sun hours by region
Peak sun hours are not the same as daylight hours: they count the time the sun is strong enough to count as full output, averaged across the year. Use the range for your region as a starting point in the calculator.
| Region | Peak sun hours per day (approximate) |
|---|---|
| Southwest (AZ, NV) | 6–7 |
| California & Florida | 5.5–6 |
| Southeast | 5–5.5 |
| Midwest | 4.5–5 |
| Northeast | 4–4.5 |
| Pacific Northwest | 3.5–4 |
The spread matters. The same 900 kWh home needs roughly a third more panels in the Pacific Northwest than in Arizona, which is why a quote from a sunnier state is never a safe guide to your own roof.
Panel sizes and roof space
Most home solar panels sold today are rated between 370 and 430 W, and a typical panel measures about 17.5 sq ft — roughly five and a half feet long by just over three feet wide. Wattage changes the count, not the size of the job: a 7.5 kW requirement takes 21 panels at 370 W, 19 at 400 W or 18 at 430 W. The calculator allows 17.5 sq ft per panel, but a real layout also needs setbacks from ridges and edges and room around chimneys and vents, so treat the roof figure as a minimum.
What decides cost and payback
Two systems of the same size can pay back years apart. The biggest lever is your electricity rate: the production that saves $155 a month at $0.17/kWh saves about $274 a month at $0.30/kWh, which is why solar pays back fastest where electricity is expensive. The second lever is what your utility pays for exported power. Full-retail net metering credits every exported kilowatt-hour at the rate you would have paid, while wholesale export rates pay a fraction of that, and the gap can add years. Shading and roof direction move the answer too. The calculator gives you the size and the ballpark; an installer survey gives you the rest.
What to calculate next
Before you commit, run two neighbouring checks. The Electricity Cost Calculator shows what your appliances cost to run now — the spending solar has to beat. The Roofing Calculator helps you check your roof first: its age and condition decide whether it should be repaired or replaced before panels sit on top of it for the next 25 years. For the full set of tools, see the Calculators hub.
Solar guides
Go deeper with our two solar guides — one sizes a system from your monthly usage, the other works out when it pays for itself.
How Many Solar Panels Do I Need?
Panels by monthly usage — quick table, the sizing formula and roof-space maths.
Solar Panel Payback Period: When Does Solar Pay Off?
When solar pays for itself after the federal credit ended — worked examples at different rates.
Frequently asked questions
How many solar panels do I need for 900 kWh a month?
About 19 panels of 400 W at 5 peak sun hours a day — a 7.6 kW system. The exact count moves with your sun hours and panel wattage, which is why the calculator asks for both.
Is the 30% federal solar tax credit still available?
No. The federal residential credit under Section 25D ended on 31 December 2025, so a system installed in 2026 gets no federal credit. State and local incentives still vary by where you live.
How much does a 7.6 kW solar system cost in 2026?
About $22,800 at $3.00 per watt installed, before any state or local incentives. Quotes vary with roof complexity, equipment and local labour, so compare at least two installers.
What if my roof is shaded or faces north?
Expect production below these estimates, sometimes well below. The calculator assumes a clear, well-oriented roof, so a site assessment matters more than any calculator for a shaded or north-facing roof.
Estimates only — get two or three installer quotes; your roof, shading and utility rules decide the real numbers.