You exercised incentive stock options and paid alternative minimum tax on the spread — a bill on paper gains you never received in cash. That is the well-known ISO trap.
The less-known part is that the tax you paid was not simply lost. Timing differences that trigger AMT generate a credit against future regular tax, which recovers it over subsequent years.
Most of the people who paid it do not claim it, because nobody tells them and it requires tracking across years.
What changed in 2026
- Exemption amounts continued adjusting. The thresholds at which AMT applies move annually.
- Awareness of the credit stayed low. Despite being long-standing, it remained frequently unclaimed.
- Dual basis tracking got easier. Better software support for tracking the two basis figures reduced errors.
- The underlying mechanics were unchanged. This is established law rather than a recent provision.
Where the credit comes from
Alternative minimum tax is a parallel calculation. You compute your tax both ways and pay the higher.
Some items causing AMT are timing differences — they accelerate income into the AMT calculation that regular tax will recognise later. An ISO exercise is the classic case: AMT counts the spread as income now, while regular tax counts nothing until you sell.
Because the difference is timing rather than permanent, tax paid on it generates a credit. When the timing reverses — typically when you sell the shares — you become eligible to recover it.
Items that are permanent differences rather than timing ones do not generate a credit. Only the timing portion does.
When you can use it
The credit is available in a year when your regular tax exceeds your tentative minimum tax — that is, a year you are not in AMT — and it is limited to the difference.
That constraint is what makes recovery slow. If you remain in AMT, the credit sits unused. It carries forward indefinitely and does not expire, and it may take several years to recover a large credit.
| Situation |
Credit usable? |
| Still in AMT |
No — carries forward |
| Regular tax exceeds AMT slightly |
Partially, up to the difference |
| Regular tax comfortably exceeds AMT |
Yes, up to the difference |
| Large credit, small annual difference |
Recovered over many years |
Selling the ISO shares frequently helps, because it creates a large difference between the two calculations — the shares have a higher basis for AMT purposes than for regular tax, so the gain reported for AMT is smaller, which reduces tentative minimum tax and creates room for the credit.
Dual basis
The bookkeeping requirement that produces errors.
After an ISO exercise, the shares have two different bases: the exercise price for regular tax purposes, and the fair market value at exercise for AMT purposes.
Every subsequent calculation must use the right one. Selling the shares produces a different gain in each system, and that difference is frequently what unlocks the credit.
Tracking both across years, potentially across multiple exercises at different prices, is genuinely fiddly. Records from the year of exercise are essential, and reconstructing them later is difficult.
This is the practical reason so many credits go unclaimed: the information needed sits in a return from several years ago that nobody revisited.
Common mistakes
- Not knowing the credit exists. The most common and most expensive.
- Failing to carry it forward. It must be tracked year to year on your return.
- Not tracking dual basis. Prevents the calculation entirely.
- Discarding exercise-year records. Needed years later.
- Assuming it expires. It carries forward indefinitely.
- Changing preparers without transferring the carryforward. A frequent way it gets lost.
- Exercising further ISOs while carrying a credit. May keep you in AMT and block recovery.
FAQ
How long does recovery take?
Entirely dependent on the size of the credit and the annual difference between your regular tax and tentative minimum tax. Several years is common for a large credit.
Does the credit expire?
No — it carries forward indefinitely until used.
What if I never sell the shares?
The credit still carries forward and may be usable in years you are not in AMT for other reasons. Selling typically accelerates recovery by creating a larger difference.
Can I claim it for a prior year I missed?
Amending prior returns may be possible within the applicable window. Given the amounts frequently involved, checking whether you have an unclaimed credit is worth the professional time — see ISO AMT explained.
Where to go next
For the exercise decision that creates the liability, read ISO AMT explained and ISOs vs NSOs. For the eventual sale treatment, capital gains tax explained.
This is general information, not tax advice. AMT and credit calculations are complex and record-dependent; consult a qualified professional.