Alternative Minimum Tax (AMT)

The alternative minimum tax is a parallel tax system that can matter a lot for startup employees who exercise incentive stock options (ISOs) and hold the shares.

If you have heard a horror story about someone exercising options and getting a surprising tax bill before any liquidity event, AMT was often part of that story.

Why AMT shows up in startup equity planning

With ISOs, exercising can be relatively friendly under the regular tax system. But for AMT purposes, the spread between the strike price and the fair market value at exercise may count as an adjustment.

In plain English: you can owe tax based on paper gains even when you still hold illiquid stock.

When employees most often run into AMT

AMT risk tends to rise when:

• the company’s fair market value has increased significantly
• your strike price is low relative to current value
• you exercise a large number of ISOs in one tax year
• you plan to hold the shares instead of selling immediately

Why employees sometimes still exercise

Because the upside can still be worth it.

Exercising earlier can:

• start the holding period clock
• potentially position you for capital-gains treatment later
• reduce future spread if the company continues to appreciate

The challenge is balancing that upside against tax cost, cash needs, and liquidity risk.

Practical questions to model

How much spread exists today?

The wider the gap between strike price and fair market value, the more AMT attention the exercise may require.

What happens if the company’s value falls later?

This is the classic pain point: you can pay tax on value that later disappears.

Could a staged exercise make more sense?

Some employees spread exercises across tax years rather than doing everything at once.

Do you have cash for both the exercise and the tax?

The answer needs to be “yes” before the strategy is viable.

Common AMT mistakes

Exercising based on optimism alone

Belief in the company is not a tax plan.

Forgetting that private-company FMV can change

A rising 409A can make “I’ll do it next year” much more expensive.

Not tracking potential AMT credits

In some circumstances, AMT paid may help generate future credits, but that does not solve the cash-flow problem in the year of exercise.

Final takeaway

AMT is one of the main reasons ISO planning is not just “exercise early and hold.” The best move depends on the spread, the number of shares, your available cash, and your willingness to hold illiquid concentrated stock.

Related guides

• Incentive Stock Options (ISOs)
• Capital Gains Tax on Startup Shares
• Should You Borrow From Your 401(k) to Exercise Options?

Sources and further reading

• IRS Topic No. 427, Stock Options: https://www.irs.gov/taxtopics/tc427
• IRS Publication 525: https://www.irs.gov/publications/p525