Financing
Enter your loan details and an extra monthly amount you're considering. See exactly how much interest and time that extra payment saves.
How it works
Step 1
Check your loan agreement first, or use the prepayment penalty cost calculator if you're unsure whether one applies.
Step 2
Use an extra monthly amount you can comfortably sustain every month, not just a one-time figure, since consistency matters for this calculation. The loan payment calculator can help confirm your baseline payment first.
Step 3
Ask specifically how to designate extra payments so they reduce your balance rather than simply prepaying a future month's regular payment.
Every extra dollar applied to principal stops accruing interest for the rest of the loan, and that effect compounds every single month it continues. On a $28,000 loan at 6.99% APR over 20 years, adding just $50 a month saves about $8,663 in total interest and shortens the payoff by roughly 6 years and 5 months, a substantial result from a relatively small monthly commitment. The CFPB's explainer on how loan amortization works covers the underlying mechanics behind this effect.
Because less interest accrues each month as the balance shrinks faster, more of every subsequent payment goes toward principal too, creating a snowball effect. That's why a $50 extra payment doesn't just shave off proportional months, it accelerates the payoff more than a simple linear calculation would suggest.
A steady extra payment every month works alongside, not instead of, a lump-sum paydown. If your system was installed by December 31, 2025, and you have unused credit carrying forward, the carried-forward credit tool covers that lump-sum piece specifically, while this tool handles the ongoing extra payment strategy for anyone, regardless of credit eligibility. Before you settle on this figure, the federal solar tax credit calculator is worth a run to see which credits apply to you.
Confirm that extra payments get applied to principal immediately rather than held as a credit toward a future scheduled payment, since the latter doesn't reduce interest the same way. Also confirm there's no prepayment penalty, which the prepayment penalty cost calculator can help estimate if one applies, and the CFPB's prepayment penalty explanation covers what to look for in your loan agreement.
If you want to see exactly how the balance declines month by month under either scenario, the amortization schedule generator lays out the complete payment breakdown for your standard loan terms. The total cost of ownership calculator and federal solar tax credit calculator can help you see how an early payoff fits into the bigger financial picture. The total cost of ownership calculator is a useful next step once you have this result.
Questions
It adds up more than most people expect. On a $28,000 loan at 6.99% APR over 20 years, adding just $50 a month in extra principal payments saves about $8,663 in total interest and pays off the loan roughly 6 years and 5 months early.
Most lenders require you to specify that any extra amount goes toward principal, not simply as a payment for a future month, or it may not reduce the balance the way you intend. Check with your servicer on how to properly designate extra payments as principal-only.
Both reduce interest, and the total savings depend mainly on how early the extra money reaches the balance and how much is applied overall. A single early lump sum can be very effective, while consistent smaller extra payments compound their benefit every month they continue.
Yes, this is worth checking first, since a penalty could offset some of the savings from paying extra. Most solar loans don't carry one, but the prepayment penalty cost calculator can help you estimate the cost if yours does.
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