You exercised your ISOs. Smart move—you got in early, strike price was low, and the company's trajectory looks great.
Then April comes around and your tax advisor says: "You owe $47,000 in AMT."
Wait, what?
You didn't sell anything. You don't have the cash. The shares aren't even liquid yet. How can you owe $47,000?
Welcome to the Alternative Minimum Tax. The tax trap that's crushed more startup employees than any market crash.
What the Hell Is AMT?
The Alternative Minimum Tax is a parallel tax system designed to prevent wealthy people from using deductions and credits to zero out their tax bill.
Here's how it works:
- You calculate your taxes under the normal system
- You calculate your taxes under the AMT system
- You pay whichever is higher
The AMT system has fewer deductions, different rates, and—here's the kicker—it treats ISO exercise as taxable income even though you haven't sold anything.
Under regular tax rules, exercising ISOs isn't a taxable event. You only pay tax when you sell.
Under AMT rules, the spread between your strike price and the fair market value at exercise is added to your income. Not real income. Phantom income.
You owe taxes on money you don't have.
The Math That Bankrupts People
Let's say you exercise 20,000 ISOs:
- Strike price: $1/share
- Fair market value at exercise: $15/share
- Spread: $14/share
- Total AMT income: 20,000 × $14 = $280,000
That $280,000 gets added to your income for AMT purposes. If you're already making $150K in salary, your AMT income is now $430,000.
AMT rates are 26% up to approximately $232,600, then 28% above that. Your AMT bill on the ISO exercise alone could be $75,000+.
You just spent $20,000 to buy the shares. Now you owe another $75,000 to the IRS. And the shares are illiquid because your company is still private.
This is the trap.
Why This Destroyed People in 2000-2002
During the dot-com boom, thousands of employees exercised ISOs at high valuations. They paid massive AMT bills. Then the companies went bust, and the shares became worthless.
But the IRS still wanted its money.
People owed six-figure tax bills on stock that was now worth $0. They couldn't pay. They went bankrupt. Congress eventually passed some relief provisions, but the damage was done.
The AMT trap bankrupts people not because they're reckless, but because they followed the rules and got screwed by illiquidity.
How to Calculate Your AMT Exposure
You can't avoid AMT entirely if you're exercising ISOs, but you can manage it. Here's the formula:
AMT Income = Regular Income + (FMV at exercise – strike price) × number of shares exercised
Then:
- Subtract AMT exemption ($85,700 for single filers in 2024, phases out at higher incomes)
- Apply AMT rates: 26% on first approximately $232K, 28% above that
- Compare to your regular tax liability
- Pay the higher amount
Your AMT liability is the difference between your AMT bill and your regular tax bill.
Example:
- Regular tax: $40,000
- AMT: $95,000
- AMT liability: $55,000
You owe an extra $55,000 because of ISO exercise. Ouch.
Strategies That Actually Work
1. Exercise up to the AMT threshold (no more)
You can exercise some ISOs without triggering AMT if you stay under the exemption amount. This is called "exercising to the AMT crossover."
Work with a tax advisor to calculate how many shares you can exercise without triggering AMT. Then exercise that amount each year.
This is the slow-and-steady approach. It takes longer, but you avoid the AMT trap.
2. Exercise early (when the spread is small)
If you exercise ISOs when the strike price and FMV are close (ideally, within the first 90 days of getting the grant), the spread is small or zero.
No spread = no AMT income.
The downside? You're putting cash into an illiquid, risky asset very early. If the company fails, you lose everything. But if it succeeds, you've locked in a tiny spread and avoided AMT.
3. Disqualifying disposition (intentionally)
If you sell the stock within 1 year of exercise OR within 2 years of grant, it becomes a "disqualifying disposition." You lose the favorable ISO tax treatment and it gets taxed like an NSO.
But here's the upside: no AMT.
If you know you'll need to sell quickly (because you can't afford to hold illiquid stock), exercise and sell immediately as a disqualifying disposition. You'll pay ordinary income tax on the spread, but you'll have cash to pay the tax.
4. Exercise and sell in the same year (cashless exercise)
If your company allows same-day sales (usually only post-IPO), you can exercise and sell immediately. The spread gets taxed as ordinary income, but you have the cash to pay it.
No AMT. No illiquidity risk. Clean and simple.
5. AMT credit carryforward
If you do get hit with AMT, you generate an AMT credit that can be carried forward to future years. When your regular tax exceeds your AMT in a future year, you can use the credit to reduce your bill.
BUT: you only get the credit back if you have future years with regular tax > AMT. If the company goes bust and you never have high income again, you may never recover the credit.
This is not a reliable safety net.
What to Do Right Now
If you're considering exercising ISOs:
- Get a copy of your company's most recent 409A valuation (this determines FMV)
- Calculate the spread: (FMV minus strike price) × number of shares
- Run an AMT projection with your tax advisor
- Determine how many shares you can exercise without triggering AMT
- Only exercise what you can afford to lose (remember: the shares are illiquid)
If you've already exercised and are facing an AMT bill:
- Make sure you're tracking the AMT credit for future years
- Do NOT exercise more ISOs this year
- Set aside cash now to pay the bill in April
- Consider a disqualifying disposition if liquidity is critical
If your company just raised a round at a high valuation:
- Your 409A is about to jump
- If you were planning to exercise, do it BEFORE the new 409A kicks in
- Once the FMV goes up, your AMT exposure goes up
The Bottom Line
AMT is the reason most financial advisors tell you to be very careful with ISOs. The tax treatment looks great on paper—until you realize you're paying taxes on illiquid stock you can't sell.
If you're going to exercise ISOs:
- Do it early when the spread is small
- Only exercise up to the AMT threshold each year
- Have a plan for liquidity (IPO, acquisition, secondary market)
- Never exercise more than you can afford to lose
And if your tax advisor tells you you're about to trigger $50K in AMT? Listen to them.
This is the one tax trap that can wipe out years of wealth building in a single filing season.
This article is for educational purposes only and does not constitute tax advice. Consult a qualified tax professional regarding your specific situation.
Securities offered through LPL Financial, Member FINRA/SIPC. Investment advice offered through Great Valley Advisor Group, a registered investment advisor and separate entity from LPL Financial.
Chesapeake Financial Planners | 2402 Scotlon Ct, Forest Hill, MD 21050 | (410) 652-7868 | www.chesapeakefp.com
