Financing
Enter your loan amount, APR, and term. See the exact total interest over the full loan, plus how much of your first three years goes to interest versus principal.
How it works
Step 1
Use your actual loan quote if you have one. The loan term comparison tool can help you compare interest totals across several terms at once.
Step 2
Interest as a percent of the loan gives you a quick sense of how much extra you're really paying, which can be a useful number to compare across different lender quotes, alongside the loan APR impact calculator.
Step 3
The year-by-year breakdown shows how much of your early payments go toward interest versus principal, which explains why the balance drops slowly at first.
On a $28,000 loan at 6.99% APR over 20 years, total interest comes to about $24,060, nearly 86% of the original loan amount. That number often surprises people, since the monthly payment feels manageable while the total interest, spread across 20 years, adds up to nearly as much as the system itself. The CFPB's explainer on how loan amortization works covers why interest accumulates this much over a long term.
Interest accrues on the outstanding balance each month, and that balance is at its highest right at the start of the loan. In year 1 of a typical $28,000, 20-year loan, roughly $1,936 of the year's payments go to interest against only about $667 to principal, a ratio that gradually flips as the balance shrinks over the loan's life. The total cost of ownership calculator can help you see this alongside your full ownership costs.
Because interest accrues over more months on a longer term, stretching the same loan amount across more years significantly increases total interest, even though the monthly payment drops. Run the loan term comparison tool to see this tradeoff across all the common term lengths side by side.
Any extra payment applied directly to principal reduces the balance interest is calculated on for every remaining month, which compounds into meaningful savings over a multi-year loan. The early payoff savings calculator shows exactly how much a specific extra payment amount saves in total interest. The federal solar tax credit calculator is worth checking too if a carried-forward credit could serve as that extra payment.
This tool shows the first three years of the interest-versus-principal split. For the full schedule across the entire loan term, the amortization schedule generator lays out every single payment from start to finish. The CFPB's issue spotlight on solar financing covers general financing considerations worth reviewing alongside this breakdown.
Questions
It depends on the loan amount, APR, and term, but on a $28,000 loan at 6.99% APR over 20 years, total interest comes to about $24,060, close to 86% of the original loan amount. A shorter term or lower rate reduces that figure substantially.
Loan interest is calculated on the remaining balance each month, so early in the loan when the balance is highest, more of each payment goes toward interest. As the balance shrinks over time, a growing share of each payment goes toward principal instead, even though the total payment stays the same.
No, this figure is purely the interest cost of the loan itself. A federal tax credit, where it still applies, such as for a system installed by December 31, 2025, with unused credit carrying forward, is calculated on the system's price and isn't connected to how the loan accrues interest, though applying it as a paydown can reduce future interest.
Yes, making extra principal payments, if your loan allows it without a penalty, reduces the balance interest is calculated on, cutting the total interest paid over the remaining term. The early payoff savings calculator shows exactly how much a specific extra payment amount would save.
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