Taxes & Equity Comp: Alternative Minimum Tax Surprises

Aug 6

TL;DR

AMT is a separate tax system that can hit you hard when exercising ISOs—even if you don’t sell a single share.
The tax is based on the spread between your exercise price and market value, a “paper gain” with no cash in hand.
Plan ahead: exercising strategically and using AMT credits can help you avoid (or at least soften) the blow.

The Tax Bill on Stock You Didn’t Sell

You finally decide to exercise your Incentive Stock Options (ISOs). You’ve been waiting for this. You believe in the company, the FMV is up, and you’re playing the long game.

Then tax season hits. Your accountant gives you a look. You owe $50,000 in taxes.

"But I didn’t even sell the shares," you say.

Welcome to the strange world of the Alternative Minimum Tax (AMT)—where you can pay real money on gains you haven’t realized.

What Is AMT, and Why Should You Care?

AMT is a parallel tax system designed to ensure high-income earners pay at least a minimum amount of tax, even if they qualify for a bunch of deductions under the regular system. It was meant to target the ultra-wealthy.

But in practice it often hits startup employees and tech professionals who exercise ISOs. Not because they made tons of money. But because they might have—on paper.

Depending on your income level, AMT can apply when ISOs are exercised and held beyond the end of the tax year. If you exercise ISOs and sell them within the same calendar year, AMT will not be relevant, as that sell would trigger ordinary income on the gains.

Why ISO Exercises Trigger AMT

When clients consider AMT, it is almost always in the context of Incentive Stock Options (“ISOs”).

ISOs come with a special tax benefit: if you hold the shares long enough, you may qualify for long-term capital gains instead of ordinary income tax.

But the catch is when you exercise ISOs, the IRS considers the difference between your strike price and the fair market value (FMV) as income for AMT purposes. Even if you don’t sell a single share.

Example:

You exercise 10,000 ISOs at $2/share strike price when the FMV is $20/share.

That’s an $18/share spread.
Could represent up to $180,000 in AMT income taxed as high as 28% depending on your other income.
This could be over $50K in taxes for assets you don’t even have access to.

No cash changes hands. But you could owe thousands in taxes.

This is the part that catches people off guard. AMT isn’t just theoretical. It’s a real tax bill based on unrealized gains. You might owe tens of thousands before you make a single dollar from selling your stock.

Even worse: if the stock price drops after you exercise, you’re still on the hook for the AMT based on the higher FMV at the time of exercise.

So why would anyone do this?

Exercising ISOs early and holding allows for the shares to potentially qualify for long-term capital gains (“LTCG”) tax treatment on the gain, whereas an ISO exercise that is sold within 1-year has ordinary income tax treatment. The highest federal tax bracket for LTCG is ~23.8% (20% Federal + 3.8% NIIT), whereas the highest federal tax bracket for ordinary income is 37%. So for high earners, this is a 15% tax delta, which can be very meaningful when considering material equity exits.

Strategies to Manage the AMT Hit

The good news is there are ways to manage AMT risk if you plan ahead.

Early Exercise: If you can exercise when FMV is close to your strike price (often early in your vesting schedule), the AMT hit may be minimal.
Staggered Exercises: Spread your exercises across years to stay under AMT exemption thresholds.
Disqualifying Dispositions: Sometimes it makes sense to intentionally sell within a year and take the ordinary income hit to avoid AMT. However, this is less practical for startups without easy liquidity.
AMT Projections: Work with a tax advisor and run the numbers before exercising. It can save you big.
Know Your AMT Credit: If you do pay AMT, you may be able to recover some of it in future years through the AMT credit. It’s not immediate, but it helps.

The AMT Credit point is a critical one: employees hit by high AMT taxes typically can earn this back over multiple years by getting a tax credit.

Let’s say you exercised ISOs that triggered AMT in order to qualify for long-term capital gains, and then after the 1-year mark, you sold the shares. To make things simple, let’s assume the market value is the same as it was when you exercised. In our example from above where the employee owed potentially $50K, if their actual realized tax rate after long-term capital gains is accounted for is less than they paid in AMT taxes, they could be eligible for a future tax credit.

From this perspective, early ISO exercise is often prepaying taxes today for a future lower rate.

The Long Game: Plan, plan, plan

AMT doesn’t mean you made a mistake. It just means the tax code wasn’t built with modern equity comp in mind.

Stay proactive:

Track your vesting schedule and 409A valuations.
Coordinate with your CPA before year-end.
Be aware of state-specific rules—some states (like CA) conform to federal AMT, others don’t.
Discuss with your financial advisor well before any exercise so they can take this into account.

This is one of the clearest cases where good planning makes a huge difference.

If you’re holding ISOs, don’t wait until April to understand your AMT risk. Do a dry run in Q3 or Q4. Even better? Build a long-term strategy that aligns your equity with your cash flow and tax exposure.

Disclaimer: This content is for informational purposes only and does not constitute legal or tax advice. Any numbers and estimates are hypothetical. Please consult your advisor and accountant before making any financial decisions.

William Cole