What is AMT on ISO exercise?

Exercising incentive stock options (ISOs) and holding the shares can trigger the Alternative Minimum Tax (AMT), a parallel tax system that adds back the "bargain element" — the gap between what you paid and what the shares are worth — as taxable income, even though you haven't sold anything and have no cash from a sale. You calculate your tax both ways and pay whichever is higher.

Priya is a software engineer at a private company. Her ISOs have a strike price of $2 per share, and the company's most recent 409A valuation puts the fair market value at $22 per share. She exercises 10,000 options, writing a $20,000 check to her employer for shares that are worth $220,000 on paper. She doesn't sell a single share. A few months later, her accountant tells her she owes tens of thousands of dollars in tax anyway.

Key points

• Exercising ISOs and holding the shares creates a $200,000 "bargain element" that counts as income for AMT purposes only — not for regular tax.
• You calculate your tax liability twice (regular tax and AMT) and pay the higher amount; the difference is your AMT.
• The tax bill can arrive before you've sold any stock or received any cash, which is the single biggest risk of early ISO exercise.

Why AMT exists, and why options trigger it

The regular tax system lets you use deductions, exclusions, and preferential treatment to lower your bill. Congress created the AMT decades ago as a backstop: a second, simpler calculation with fewer breaks, designed to make sure people with large tax preference items still pay a meaningful amount of tax. If your AMT liability comes out higher than your regular tax liability, you pay the AMT amount instead.

The two systems run in parallel every year, whether or not you have equity comp. For most W-2 employees with no ISOs, no large state tax deductions, and no unusual preference items, AMT never comes into play because regular tax is almost always higher. Equity comp changes that calculus, because it introduces one of the AMT's biggest preference items: the ISO bargain element.

ISOs get favorable regular-tax treatment: no tax is due at exercise, and if you hold the shares long enough, the eventual gain can be taxed at capital gains rates instead of ordinary income rates. AMT closes part of that gap. For AMT purposes only, the spread between your strike price and the stock's fair market value on the day you exercise — the bargain element — is added to your income in the year you exercise, whether or not you sell.

Think about it this way: regular tax treats the exercise as a non-event because you haven't converted anything to cash. AMT treats the exercise as if you'd already captured the paper gain, because from a "did your net worth go up" perspective, it did — you now hold something worth more than you paid for it.

The bargain element: phantom income with no cash behind it

The bargain element is simply:

Fair market value at exercise − Strike price, multiplied by the number of shares exercised.

For Priya, that's ($22 − $2) × 10,000 shares = $200,000. That $200,000 is often called "phantom income" because it behaves like income for tax purposes but produced zero cash in her bank account. This mismatch — real tax bill, no real cash — is the central risk of exercising ISOs early or exercising a large batch at once, especially at a private company where you can't simply sell a few shares to cover the tax.

A worked example

Let's walk through Priya's numbers in full. She's single, her 2026 W-2 salary is $160,000, and she takes the standard deduction of $16,100 for single filers. She exercises 10,000 ISOs at a $2 strike price when the fair market value is $22 per share, and holds the shares (no sale in the same year).

Step 1: Calculate the bargain element. ($22 − $2) × 10,000 = $200,000

Step 2: Build AMT income (AMTI). Start from taxable income before the AMT adjustment, add back the bargain element, and add back a few common items regular tax allows that AMT doesn't (Priya has no state and local tax itemizing beyond the standard deduction, so her main add-back is the ISO spread itself).

• Regular taxable income (salary minus standard deduction): $160,000 − $16,100 = $143,900
• Plus ISO bargain element: + $200,000
• AMTI = $343,900

Step 3: Subtract the AMT exemption. For 2026, the AMT exemption for single filers is $90,100, and it doesn't start phasing out until AMTI exceeds $500,000 — Priya is well under that, so she gets the full exemption (IRS).

$343,900 − $90,100 = $253,800 of AMT taxable income.

Step 4: Apply the 26%/28% AMT rates. For 2026, the 26% rate applies to the first $244,500 of AMT income above the exemption, and 28% applies above that (Tax Foundation).

• 26% × $244,500 = $63,570
• 28% × ($253,800 − $244,500) = 28% × $9,300 = $2,604
• Tentative minimum tax = $63,570 + $2,604 = $66,174

Step 5: Compare to regular tax. Priya's regular tax on $143,900 of taxable income (2026 single brackets) works out to roughly $26,700 using the standard progressive brackets.

Step 6: The difference is her AMT. $66,174 (tentative minimum tax) − $26,700 (regular tax) = $39,474 of AMT that Priya owes on top of her regular tax bill, purely because she exercised and held ISOs worth $200,000 more than she paid for them — without selling a single share.

That's a real check she has to write, from cash she may not have set aside, for a gain that exists only on paper until the company has a liquidity event.

A few things would have made Priya's bill smaller or larger. Exercising fewer shares in a given calendar year reduces the bargain element and can keep her under the AMT threshold entirely. Exercising early in a company's life, when the spread between strike price and fair market value is small, does the same thing — this is the core logic behind early-exercise programs. Waiting until right before an IPO, when the spread is often largest, tends to produce the biggest AMT bills, precisely when the shares are least liquid.

The formula

Bargain element = (FMV at exercise − Strike price) × Number of shares exercised

AMT income (AMTI) = Regular taxable income + Bargain element + other AMT add-backs

AMT base = AMTI − AMT exemption (phases out above certain income levels)

Tentative minimum tax = 26% × (AMT base up to $244,500)
                       + 28% × (AMT base above $244,500)

AMT owed = Tentative minimum tax − Regular tax liability (if positive)

The AMT you pay isn't gone for good

Here's the part most people miss in the panic of a surprise tax bill: the $39,474 Priya pays isn't a permanent penalty. Because she paid AMT specifically due to a timing difference (the ISO exercise), she generates an AMT credit she can use in future years when her regular tax exceeds her AMT — for example, the year she finally sells the shares. That mechanism is its own topic; see how the AMT credit works and how to recover it.

How WealthOS helps

WealthOS connects to your option grants and 409A or public market price data to estimate your AMT exposure before you exercise, not after you get the tax bill. Model different exercise sizes and timing scenarios against your actual salary and filing status to see the AMT impact in dollars, not guesswork.

Related reading

• The AMT credit, explained
• ISO vs. NSO tax differences
• The $100k rule: how it splits your ISOs and NSOs
• Should you exercise before an IPO?

Sources

• IRS: 2026 tax inflation adjustments, including AMT exemption amounts
• IRS Instructions for Form 6251 (Alternative Minimum Tax — Individuals)
• Tax Foundation: 2026 Tax Brackets and Federal Income Tax Rates

This article is educational and not tax, legal, or financial advice. Talk to a CPA or tax advisor about your specific situation.