California's State AMT on ISOs: The Extra 7% Layer Most Planners Miss

A principal engineer at a Bay Area AI company exercised 30,000 ISOs in December 2025 with a strike of $2.90 and a 409A of $41. Bargain element: $1,143,000. Her federal AMT for the exercise came to approximately $298,000. Her CPA flagged the California state AMT separately: another $64,000. Total AMT across federal and state: $362,000. The California layer was 22% of the federal number, not trivially small. She had cash for the federal; she had to liquidate a taxable brokerage account to cover the state.

California is one of five states with a functioning AMT system for individual taxpayers. The California rate is 7% on state-adjusted AMTI. The mechanics parallel the federal but with California-specific rules on deductions, exemptions, and preferences. For any California resident making a substantial ISO exercise, the state AMT is a material planning consideration separate from the federal.

The California AMT framework

California’s AMT is codified in Cal. Rev. & Tax. §§17062 and following. The computation is done on California Form 5805 Schedule P (540) and flows through to the main return.

The California AMT rate is 7%, flat, applied to California-adjusted AMTI after the California AMT exemption. There is no two-tier structure like the federal 26%/28%.

The California exemption

For 2025, the California AMT exemption is:

Filing status	California AMT exemption	Phase-out starts	Fully phased out
Single	$90,768	$340,381	$703,453
Married filing jointly	$121,025	$453,846	$937,946

The exemption phases out at 25 cents per dollar of AMTI above the phase-out start. The phase-out thresholds are substantially lower than the federal ($626,350 single, $1,252,700 MFJ), so California residents hit the phase-out at much lower income levels than federal.

The California adjusted AMTI

California AMTI begins with federal AMTI and then applies California-specific adjustments. Key differences:

California does not allow a deduction for state and local taxes, because California already disallows the SALT deduction as a preference. The federal SALT-addback is not needed for California.
California allows deductions that the federal AMT disallows, such as certain standard deduction differences.
California has its own treatment of QSBS: prior to 2013, California allowed a partial §1202 exclusion; current law requires full inclusion for state purposes. The gap creates a significant California-specific tax on QSBS-exempt federal gain.

For pure ISO exercisers, California AMTI is roughly federal AMTI minus the federal SALT addback (if any). The resulting number is then subjected to California’s 7% rate after California exemption.

The combined federal-state picture

Consider a Bay Area single filer with:

W-2 wages: $420,000
ISO bargain element: $1,143,000
Standard deduction (federal)
California SALT paid
Other items typical

Federal side:

Federal AMTI: approximately $1,563,000
Federal exemption: fully phased out at this level
Federal TMT: approximately $432,000
Federal regular tax: approximately $135,000
Federal AMT: approximately $297,000

California side:

California AMTI: approximately $1,515,000 (close to federal AMTI, adjusted for state differences)
California exemption: fully phased out
California TMT: 7% × $1,515,000 = $106,050
California regular tax: approximately $42,000 (at California brackets)
California AMT: approximately $64,000

Combined AMT: $297,000 + $64,000 = $361,000 on a $1,143,000 bargain element. Effective AMT rate: 31.6%.

Why the state matters more than the rate suggests

California’s 7% rate seems small compared to the federal 26%/28%. The state layer is meaningful for three reasons.

The California exemption phases out earlier

At $340,381 of AMTI (single), the California exemption starts to phase out. A large ISO exercise can push the exemption to zero well before the federal exemption starts phasing out at $626,350. An employee with $420,000 of other income exercises once and loses the entire California exemption before touching the federal.

No deduction for state AMT paid

Unlike many state income taxes, state AMT paid is not deductible federally in the same way. The federal calculation of AMTI disallows the state tax deduction as a preference item anyway. The state AMT cost is effectively on top of the federal, with no federal offset.

California AMT credit has different mechanics

California has its own AMT credit system on Schedule P, but the credit mechanics differ from federal in subtle ways. California also applies the credit only against California tax. Moving out of California after a state AMT payment can strand the credit.

The residency and moving consideration

Large ISO exercises by California residents produce state AMT. Non-residents exercising California-sourced ISOs face similar but more complex issues. California generally sources ISO compensation to the state where the services were performed during the vesting period.

The exercise-then-move problem

An employee who exercises ISOs in California in year 1 owes California AMT in year 1. In year 2 the employee moves to Texas. The California AMT credit generated in year 1 is still there, but California only allows the credit against California tax. A Texas resident owes essentially no California tax and cannot use the credit.

Timing the exercise for immediately before a move out of California does not help. The exercise triggers California AMT as long as the exercise occurs while the employee is a California resident.

The move-then-exercise strategy

An employee who moves from California to Texas and then exercises ISOs can avoid California AMT on the exercise, provided the exercise occurs after California residency has cleanly ended. California’s rules on residency departure are strict: continuing California ties (a home, a spouse and children, California-registered vehicles) can leave the taxpayer a California resident for tax purposes despite a physical move.

California also has a “trailing nexus” concept for equity compensation earned during California residency but vested or exercised afterward. This is a complex area of California tax law that deserves its own careful review.

State AMT credit interaction with federal AMT credit

The federal AMT credit is tracked on Form 8801. The California AMT credit is tracked on California Schedule P. They are separate credits.

In a year where the employee uses federal AMT credit (because federal regular tax exceeds federal TMT), California may or may not see a similar gap. California’s regular tax rates top out at 13.3%, with TMT at 7%, so the California gap is generally large and California AMT credit tends to recover within a few years.

The federal-only strategies that California disregards

Several strategies that reduce federal AMT do not work in California.

Charitable contributions

A California charitable deduction follows federal rules, but California has different AMTI treatment of contributions than the federal. Large gifts can reduce California AMTI differently than federal AMTI.

Incentive stock option disqualifying disposition

A federal disqualifying disposition turns the ISO preference into ordinary income, absorbing the AMT impact federally. California generally follows, but California’s conformity to §422 has edge cases.

Retirement account contributions

Traditional 401(k) and traditional IRA contributions reduce both federal and California regular income, but the California AMTI treatment mirrors federal.

Year-of-exercise planning for California residents

Before exercising in California, run three calculations:

Federal AMT on the exercise at the planned bargain element.
California AMT on the exercise at the planned bargain element.
Combined tax plus federal/California credit recovery timeline.

A common California-resident strategy is to pair the exercise year with:

Maximum 401(k) and mega backdoor Roth contributions to reduce regular income (which does not reduce AMTI directly but shifts the timing).
Charitable bunching to pull deductions into the exercise year.
Deferred bonus or other compensation to smooth the income curve.

These levers reduce the total tax impact but rarely eliminate the state AMT. For a $1M+ bargain element, state AMT in California is essentially unavoidable.

Frequently asked

Is there a California AMT if I exercise while living in California and sell after moving?

The exercise triggers California AMT based on residency at exercise. The later sale, if done as a non-resident, may or may not have California tax exposure depending on sourcing rules for the compensation element.

Does California have state AMT credit recovery?

Yes, on California Schedule P. The credit applies against California tax, limited to the excess of California regular tax over California tentative minimum tax.

What happens to California AMT credit if I move to Texas?

The credit remains available but can only offset California tax. If you have no California-sourced income after moving, the credit is effectively unusable.

Does California recognize the 83(b) election for ISO early exercises?

Yes. California generally conforms to federal §83 treatment for property transferred in connection with services.

Is California AMT rate the same as regular California tax?

No. California AMT is 7% flat. California regular tax uses graduated brackets from 1% to 13.3%. TMT can be lower or higher than regular tax depending on income level and deductions.

Before you exercise as a California resident, run both the federal and California AMT projections in the AMT/ISO calculator.