You exercised your ISOs last year. You felt smart—getting in early while strike price equaled fair market value. No AMT, right?
Then April arrives. Your CPA calls. "You owe $47,000 in Alternative Minimum Tax."
You're stunned. You didn't sell anything. You don't have $47,000 sitting around. Now you're scrambling to cover a tax bill you didn't see coming—all because you missed one critical detail about how ISOs trigger AMT.
This happens every tax season to tech employees who don't understand the traps hiding in equity compensation. The difference between smart equity planning and expensive mistakes often comes down to knowing these five rules.
The 5 Most Expensive Tech Equity Tax Mistakes
Mistake 1: The ISO AMT Trap
Incentive Stock Options offer great tax treatment—exercise, hold a year, get long-term capital gains (20% vs. 37% ordinary income).
But there's a trap: Alternative Minimum Tax.
How it works: When you exercise ISOs, the IRS calculates the "bargain element" (strike price vs. fair market value). For regular income tax, no trigger. For AMT purposes? Taxable income.
Example:
- Exercise 10,000 ISOs at $5 strike
- Current FMV: $35
- Bargain element: $30 × 10,000 = $300,000
- AMT rate: 28%
- AMT bill: $84,000
You haven't sold anything. You have no cash proceeds. But you owe $84,000.
Worst part: If stock drops before you sell, you pay AMT on phantom gains that evaporated.
How to avoid it:
- Exercise ISOs only with cash reserves for potential AMT
- Work with CPA to calculate exposure beforehand
- Use AMT exemption strategically ($85,700 for single filers, 2025)
- Exercise in tranches over multiple years
Mistake 2: Missing the 90-Day Exercise Window
When you leave your company, you typically have 90 days to exercise vested options. After that? They expire. Worthless.
What you lose:
- Vested options: 25,000
- Strike: $2, Current FMV: $25
- Intrinsic value: $575,000
- Cost to exercise: $50,000
- Miss the deadline: Lose $575,000
We've seen people lose six-figure stakes because they didn't have cash ready, forgot the deadline, or assumed they had more time.
How to avoid it:
- Start saving cash 6+ months before leaving
- Mark your last day and count 90 days forward
- Read your agreement—some companies have 30-day windows
- Consider early exercise if available
Mistake 3: The Disqualifying Disposition
ISOs offer tax advantages if you follow the rules. Break them, and you convert ISOs to NSOs, losing preferential treatment.
"Disqualifying disposition" = selling ISO shares without meeting requirements:
- Hold at least 1 year from exercise date
- Hold at least 2 years from grant date
Cost: Instead of long-term gains (20%), you pay ordinary income tax (37%) on the spread.
How to avoid it:
- Track exercise dates meticulously
- Don't sell ISO shares within first year
- Set calendar reminders for qualification dates
Mistake 4: Forgetting Medicare and NIIT
You calculated federal and state taxes on your RSU vest. You set aside 45%. Covered, right?
Maybe not. Above certain thresholds, you're hit with:
- Additional Medicare Tax: 0.9% on wages over $200K (single) / $250K (married)
- Net Investment Income Tax (NIIT): 3.8% on investment income (including stock sale gains) if MAGI exceeds $200K/$250K
That "20% long-term capital gains" rate? Actually 23.8% federal (20% + 3.8% NIIT). Add state, you're at 30-35% total.
How to avoid it:
- Factor these in when calculating withholding
- Make estimated tax payments if company isn't withholding enough
- Tax-loss harvest to offset gains and reduce NIIT
Mistake 5: Not Understanding NSO Withholding
When NSOs exercise or RSUs vest, companies withhold at 22% federal (supplemental wage rate).
But if you're in the 35-37% bracket, you're severely underwitheld.
The surprise:
- RSUs vest: $200,000
- Withheld: $44,000 (22%)
- Actual rate: 47% (37% federal + 10% state)
- Actual owe: $94,000
- Tax surprise: $50,000 additional
How to avoid it:
- File new W-4 to increase withholding before large vests
- Make quarterly estimated payments
- Set aside 45-50% in separate account until taxes paid
Lesser-Known Tax Traps
State apportionment: Receive equity in one state, vest after moving to another? Tax treatment gets complicated.
Same-day sale trap: Cashless exercise works for NSOs. For ISOs, it triggers disqualifying disposition.
Wash sale rule: Sell RSUs at loss, then new RSUs vest within 30 days? IRS may disallow loss.
Tax Mistake Prevention Checklist
Before exercising:
- Calculate AMT exposure with professional
- Confirm cash reserves for exercise AND taxes
- Understand holding requirements
- Check company's 409A valuation
Before leaving company:
- Know exact exercise deadline
- Calculate exercise cost
- Determine if exercising makes sense
- Have funding plan
Before RSU vesting or stock sale:
- Model total tax liability
- Check if withholding is adequate
- Consider tax-loss harvesting
- Make estimated payments if needed
Annually:
- Review all equity transactions with CPA
- Track cost basis for all positions
- Plan for upcoming vesting
- Adjust W-4 withholding
The Bottom Line
Tech equity can be life-changing wealth—or life-changing tax bills. The difference is planning.
Employees who build lasting wealth aren't lucky with stock prices. They understood tax rules, planned ahead, and avoided traps that cost others hundreds of thousands.
Don't learn these lessons the hard way.
This content is for educational purposes only and should not be considered as tax, legal, or investment advice. Tax laws are complex and subject to change. Every situation is unique. Consult with a qualified CPA or tax professional before making equity decisions.
AMT rules are complex and vary by circumstances. Scenarios presented are simplified examples and may not reflect actual liability.
The 90-day window is common but not universal. Some companies have shorter windows. Always review your specific agreement.
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
