Every solar calculator on the internet is about to be wrong.

On December 31, 2025, the 30% federal tax credit for owned residential solar quietly expired. Most of the calculators you’ll find this year haven’t noticed.

For fifteen years, the headline number on a solar quote was the same: subtract thirty percent off the top, smile, and sign. The credit was baked so deeply into how the industry sold itself that few people bothered to ask what would happen if it ever went away. It went away. The One Big Beautiful Bill Act ended Section 25D for owned residential systems on the last night of 2025, with no phase-down.

The arithmetic of going solar in 2026 is therefore not a small adjustment to the 2024 number. It is a different calculation, with a different break-even, a different sensitivity to electricity rates, and a different answer to the lease-versus-own question. We rebuilt the math from scratch. You can run it yourself, here, with no quote and no email address.

Below: how the credit actually worked, why Section 48E for third-party-owned systems is the part that survived, and what it means for the comparison between leasing and owning in 2026.