Reading your carryforward paydown result
Who this tool is for now
The federal residential solar tax credit, Section 25D, expired for any system installed after December 31, 2025. This tool no longer applies to a new purchase or loan today. It's for homeowners who completed installation by that deadline, claimed the credit on their return for that year, and still have an unused balance to carry forward under the credit's carryforward rules, which were not affected by the expiration. The IRS Form 5695 instructions lay out the exact carryforward mechanics.
Two different ways to think about the carried-forward credit
The simplest way to look at it is subtracting the credit from the total amount paid over the loan, which gives a net cost figure. On a $28,000 loan at 6.99% APR over 20 years, that's about $43,660. But this simple subtraction doesn't reflect what actually happens if you apply the credit toward the loan balance itself once you claim it on a future return. The federal solar tax credit calculator can help you confirm the exact credit amount you're working with.
Why applying the credit as a paydown saves more
When the credit is applied as a lump-sum payment toward principal, it reduces the balance while a large share of future interest still has time to compound. On the same loan, applying an $8,400 credit as a paydown around month 14 lowers the monthly payment from about $217 to $150 for the rest of the term, and reduces total cost to roughly $36,930, a meaningful improvement over the simple subtraction figure. Compare that against a straight early payoff using a larger lump sum if you have additional cash beyond just the credit.
How the carryforward rule actually works
If your federal tax liability in the year you installed was smaller than your credit, the unused portion rolls forward to the next tax year and keeps rolling until it's fully used, with no expiration on the carryforward itself. The combined loan and rebate timing tool looks at how a credit or rebate lines up with a loan's payment schedule in more detail. The test for any loan is whether the savings beat the payment. The 25-year lifetime savings calculator in our Savings & Payback section can help you run that comparison for your system.
What happens if you skip the paydown
If you choose not to apply the credit toward the loan, either because you need the cash elsewhere or your loan doesn't require it, the loan continues at its original payment and term, and you keep the flexibility of that cash for other uses. That's a reasonable tradeoff depending on your other financial priorities.
What to confirm with a tax professional
Confirm your system's placed-in-service date, your remaining carryforward balance from Form 5695, and how it interacts with your current year's tax liability. These specifics vary by household and are worth verifying directly rather than assuming. If your system was installed after the deadline, the financing cost without ITC applied tool reflects your actual situation instead. The CFPB's issue spotlight on solar financing covers general financing considerations worth reviewing too.