Solar Loan Calculator
Enter the system cost, down payment, interest rate and term to see the monthly payment and total interest.
The solar loan calculator works out the monthly payment, total interest and total cost of a fixed-rate loan used to buy a solar system. Enter the system cost, any down payment or rebate, the interest rate (APR) and the loan term, and the page shows what you will pay each month and over the life of the loan.
It runs in your browser, so nothing you type is uploaded. It is free and needs no sign-up. You can also add your monthly electricity savings to see whether the system saves more each month than the loan payment costs.
All figures are estimates based on the numbers you enter. The starting values (15,000 at 7 % for 15 years) are only an example, not an offer or a market rate. Loan fees, dealer fees, taxes and insurance are not included, so check your loan terms before you sign anything.
How to use the Solar loan calculator
- Enter the System cost: the price on your quote, in your currency.
- Enter the Down payment or incentive paid up front. Use the cash you pay now or a rebate that lowers the amount you borrow. Enter 0 if you have neither.
- Enter the Interest rate (APR, %) from your loan offer. Enter 0 for a 0 % loan.
- Enter the Loan term (years). Decimals work, so 7.5 years is 90 months.
- Optional: enter the Monthly electricity savings to compare the payment with what the system saves each month.
- Read the results: monthly payment, amount borrowed, total interest, total of all payments, total paid including the down payment, and monthly savings minus payment if you entered savings.
- Check the year-by-year table of interest paid, principal repaid and balance.
- Open “How it was calculated” below the results to see the formula with every step using your numbers.
The example buttons above the form fill in four sample scenarios, two of them with monthly savings or a down payment, so you can see how the results change. Reset returns to the starting example.
Use Copy result to copy the result lines with a link to your calculation. Use Copy link to save the address, which stores every input so the same calculation reopens later. Print / save as PDF produces a copy with your inputs, results, steps and the date.
How do you calculate solar loan payments?
Start with the amount borrowed: the system cost minus your down payment or any rebate paid up front. Then apply the fixed-rate formula, where the monthly payment equals L × r ÷ (1 − (1 + r)^−n). Here L is the amount borrowed, r is the monthly rate (APR ÷ 12), and n is the number of months (years × 12).
For 10,000 at 6 % over 5 years, r = 0.06 ÷ 12 = 0.005 and n = 60. The payment is 10,000 × 0.005 ÷ (1 − 1.005^−60), which comes to 193.33 a month.
How much interest will I pay on a solar loan?
Total interest is the total of all payments minus the amount borrowed. Interest is charged each month on the remaining balance, so the balance is multiplied by r to get that month’s interest.
In the 10,000 at 6 % over 5 years example, the total interest is 1,599.68. For 15,000 at 7 % over 15 years, the payment is 134.82 a month and the total interest is about 9,268. Early months carry more interest because the balance is higher, and the year-by-year table shows how the balance falls over time.
Is it better to pay cash or take a loan for solar panels?
Paying cash avoids interest, so your total cost is the system price. A loan lets you spend less up front, but it adds interest and may add fees. Compare the total paid including the down payment with the cash price to see the extra cost of borrowing.
Then compare the monthly payment with your monthly electricity savings. If the payment is higher than the savings, the system costs more each month than it saves while the loan runs. The calculator shows the total paid including the down payment and the monthly payment against your savings, but it does not model a cash purchase side by side, and the choice depends on your budget.
How is a monthly loan payment calculated?
On a fixed-rate loan, the payment stays the same every month. Each payment covers that month’s interest first, and the rest reduces the balance. The interest in any month is the balance × r, and the principal repaid is the payment minus that interest.
At 0 %, there is no interest, so the payment is simply the amount borrowed divided by the number of months. For 25,000 with a 5,000 down payment at 0 % over 10 years, the amount borrowed is 20,000, and 20,000 ÷ 120 = 166.67 a month.
Worked examples
| Input | Result |
|---|---|
| cost 15000, 7 % APR, 15 years | 134.82 a month, 9,268.4 total interest |
| cost 10000, 6 % APR, 5 years | 193.33 a month, 1,599.7 total interest |
| cost 25000, down 5000, 0 % APR, 10 years | 166.67 a month, 0 total interest |
| cost 20000, down 4000, 4.5 % APR, 20 years | 101.22 a month, 8,293.7 total interest |
Calculated by the tool above with these values.
Frequently asked questions
Does the calculator include loan fees?
No. Loan fees, dealer fees, taxes and insurance are not included. Some solar loans have fees that raise the real cost, so check your loan terms and add those costs yourself.
What loan term and interest rate can I enter?
The loan term is limited to 40 years, and you can use decimals such as 7.5 years. The interest rate can be anywhere from 0 to 100 %.
Does the calculator know about rebates and tax credits?
No. It does not know about incentives. Subtract any rebate you will receive from the system cost, or enter it as the down payment, so the loan amount is what you really borrow.
Why does a longer term lower the payment but raise the interest?
A longer term spreads the same amount over more months, so each payment is smaller. Interest is charged on the balance every month for longer, so the total interest rises. Try 10 and 20 years with the same rate to compare.
Can I use the results in a quote or proposal?
Yes. Results, numbers, charts and printouts may be used freely in commercial work such as quotes, proposals, reports and service records, with no attribution needed. The figures are estimates for planning.
Is my data saved or sent anywhere?
No. Everything runs in your browser, nothing is uploaded, and no sign-up is needed. The page address stores your inputs, so anyone who has the Copy link address can see those numbers.
Related tools
- Solar payback calculator: use it to see how long the system takes to pay back its cost.
- Solar panel calculator: use it to size a panel system before you price a loan.
- Solar panel output calculator: use it to estimate how much electricity your panels will produce.
- Electricity cost calculator: use it to work out what your electricity costs, to compare with your savings.
- Solar battery size calculator: use it to choose a battery size if you plan to add storage to the system.
- All solar and battery calculators: use it to browse every tool on the site.
Sources
- Fixed-rate instalment formula with monthly compounding: Consumer Financial Protection Bureau, What is amortization and how does it work?
- Zero-interest case: payment = amount borrowed ÷ number of months (arithmetic)