What's the difference between ISOs, NSOs, and RSUs at exercise/vest?

RSUs vest as ordinary income — full federal + state tax due immediately, no decision needed. NSOs are taxed as ordinary income at exercise on the bargain element (FMV - strike). ISOs are the strange one: no regular federal tax at exercise, but the bargain element is an AMT preference item. Hold long enough (1 year from exercise + 2 years from grant) and the eventual sale qualifies for long-term capital gains. Don't hold long enough, and you've done a 'disqualifying disposition' — taxed as ordinary income, like NSOs.

What's an AMT credit and when do I get it back?

AMT paid is recoverable as a credit against future regular tax. Mechanically: each year you compute regular tax and AMT separately, pay the higher of the two, and bank the difference as a credit. In years where regular tax exceeds AMT, you can claim the credit (up to the difference). For most people this works itself out in 5–10 years, but the cash you write in April is real and the credit is illiquid until you can claim it. Some people die or move countries before fully recovering the credit.

Should I exercise early to start the LTCG holding period?

Sometimes — but not blindly. Early exercise (often allowed within 90 days of grant via 83(b) election) starts the 1-year LTCG clock immediately and keeps the bargain element near zero, minimizing AMT. The trade-off: you commit cash to shares that may be worth nothing. The math favors early exercise when (a) strike × shares is small enough that losing the cash is survivable, (b) you have high conviction in the company, (c) you'd otherwise hold the options through a future high-FMV exercise that triggers larger AMT. For mid-career people with vested ISOs at high FMV, early exercise is usually no longer available — the question is just whether to exercise now or later.

How does state AMT actually work?

Most states don't have AMT — TX, FL, WA, NV, TN, NH have no state income tax at all. CA has a strong state AMT (~7% effective on ISO bargain element). NY, IA, MN, CT have variants. The rules differ from federal AMT in subtle ways — CA conforms to most federal preferences but not all, and exemption thresholds are different. The calculator approximates state AMT as a flat percentage of bargain element, which is directionally correct but doesn't capture every nuance. If you live in a state with AMT and are exercising significant ISOs, get a CPA — the state side often costs more than people expect.

$80K AMT Bill on a $0 Stock: How ISO Exercise Goes Wrong

The IPO Was the Best Thing That Ever Happened to Marcus

Marcus joined Cloudflare-the-startup in 2018 as employee #50 with a 30,000 ISO grant at $1.50 strike. By March 2022, he was 4 years in, fully vested, and the company had IPO’d at $50/share, pulled back to $42, and was trading sideways while he waited for his blackout window to clear.

He’d read the early-employee playbook. Hold ISOs to long-term capital gains. Exercise before the price runs further. Pay AMT now, recover the credit when you sell. He ran some napkin math: 12,000 shares × ($42 - $1.50) bargain = $486K. AMT at 28% ≈ $136K. He had $200K in savings — uncomfortable but doable.

What the napkin math didn’t show:

Calculation	Marcus’s napkin	What actually happened
Bargain element	$486,000	$486,000 (correct)
Federal AMT (gross)	$136,000	$128,000 (after exemption)
Regular tax baseline	“covers most of it”	$0 — he was on sabbatical, low W-2 income
Federal AMT due	“~$30-40K maybe”	$128,000
State AMT (CA)	“small”	$34,000
Stock value 12 mo later	“still around $40”	$8.50 (post-2022 SaaS crash)
Position worth at tax day	$480K paper gain	$84K — below strike

The crash didn’t make the AMT go away. The bargain element was locked in at exercise date. He owed $162K in April for an asset now worth $102K, sitting in his account, illiquid until he sold.

Why the Math Looks Backwards

Three things make ISO timing unintuitive:

1. Bargain element is fixed at exercise, not at sale.

This is the rule that catches everyone. The IRS doesn’t care that the stock crashed after you exercised. You committed to that bargain element when you wired the strike. If FMV was $42 on exercise day and $5 on tax day, your AMTI is computed on the $42 number.

2. Regular tax baseline is what makes AMT survivable in normal years.

The federal AMT calculation produces a gross tax. The actual AMT due is the gross AMT minus your regular tax — because AMT is a parallel system meant to ensure you pay at least the AMT amount. If you’re on a high-W2-income year (say $400K), your regular tax is already paying $100K+ federal, which absorbs most of the AMT gross. Marcus made the classic mistake of exercising during a low-income year, expecting a lower marginal bracket to be a feature. It was a trap — low ordinary income meant low regular tax baseline, meaning the full AMT bill came due.

3. AMT credit recovery is real but slow.

Marcus will eventually get the $162K back. The credit is non-refundable (you can only use it to offset regular tax in years it exceeds AMT), but for someone who returns to a high-W2 career, the recovery typically completes in 5–8 years. In the meantime: $162K of capital that’s not earning a return, and could have been deployed elsewhere.

Where this scenario doesn’t apply

The Marcus case is the worst-case archetype. Counter-examples worth flagging:

Cashless exercise (same-day sale) — many companies allow simultaneous exercise + sale of enough shares to cover strike + tax. Bargain element becomes ordinary income (disqualifying disposition), but the cash matches the obligation. No AMT trap, no LTCG benefit, but no cash crisis either.
Early exercise + 83(b) — within ~90 days of grant, exercise unvested shares with bargain ≈ 0. Locks in 1-year LTCG clock from grant date. Risk: shares may be worth nothing if you leave or company fails. Best for true believers at fair compensation; not advisable if exercising would consume significant savings.
Tender offers / secondary sales — some private companies offer periodic liquidity events. These create taxable events but on real cash, not phantom. Always preferable to a paper exercise.
Strike ≈ FMV at exercise — if you exercise close to grant when 409A is still low, bargain element is small, AMT is small. The tradeoff: you commit cash to an asset that hasn’t appreciated yet.
Below-AMT-exemption exercises — if your full-year AMTI (income + bargain) sits below the exemption ($88,100 single / $137,000 MFJ for 2025), AMT is zero. This is the small-grant exception — usually applies to junior employees with ≤2,000 share grants.

What the calculator should have shown Marcus

Input	Marcus’s value
Shares to exercise	12,000
Strike	$1.50
Current FMV	$42.00
Other ordinary income	$40,000 (sabbatical)
Filing	Single
State AMT	7% (CA)
Federal marginal rate	22%

Output:

Metric	Value
Exercise cost	$18,000
Bargain element	$486,000
Federal AMT due	$128,000
State AMT due	$34,000
Total cash needed	$180,000
Break-even sale price	$15.00/share

The break-even number is the punch in the gut. He needed the stock to hold above $15 — 36% of the exercise FMV — for the exercise to be cash-neutral. It dropped to $8.50.

If he’d run this two months earlier, the right move was: exercise 4,000 shares (one-third of the position), keep AMT under $50K, leave the other 8,000 as unexercised options to revisit after the next valuation cycle. Same upside on partial position, survivable downside.

The Honesty Correction

This calculator gives you a directional estimate. Several things it doesn’t capture, all of which can move the number meaningfully:

Graduated brackets — we model your federal regular tax baseline as marginalRate × otherIncome. Real tax is graduated; the actual paid amount is somewhat lower, which means AMT due is somewhat higher than our number.
Standard / itemized deductions — these reduce regular tax further, increasing AMT due. We don’t model them.
State conformity differences — CA mostly conforms to federal AMT but has its own exemption ($83K-ish for 2025). The 7% flat assumption is a simplification.
Multi-year exercise strategies — exercising 25% per year for 4 years usually keeps each year under the bracket switch ($232,600 taxable AMTI), saving ~$30K vs a single-year exercise of the same total shares.
AMT credit timing — the calculator shows the cash you owe in April. The credit you’ll recover over 5–10 years isn’t shown because it’s not part of the immediate decision.

A CPA who specializes in tech equity will catch all of these. If your bargain element is over $200K, the $1,000–$2,000 CPA fee is the cheapest insurance you’ll ever buy.

Where this calculator falls short

No multi-year planning view — exercising 4,000 shares × 3 years saves real money over exercising 12,000 in one year, but we show single-year math.
No AMT credit projection — we don’t model when you’ll recover the AMT credit, which depends on your future income trajectory.
No NSO / RSU comparison — the same options structured as NSOs would have produced different math (immediate ordinary tax, no AMT). We don’t help you compare grant types.
No 83(b) early exercise mode — for unvested shares with bargain ≈ 0, the math is trivial but the strategy is different. We model post-vest exercises.
State AMT flat rate — CA, NY, IA, MN, CT each have variants we don’t capture precisely.

What to actually do

Run the calculator with your real numbers before you start the exercise paperwork. Strike, FMV, shares, income, state.
If federal AMT > $30K, run the math again splitting the exercise into 2–3 tax years. Most people save 15–25% with multi-year exercises that stay under the 28% bracket switch.
Verify your liquidity timing. AMT is owed by the April 15 following exercise. If you exercise December 28, you have 3.5 months to come up with the cash. If December 30, same deadline.
Get a CPA quote. A 30-minute consultation with a tech-equity-specialist CPA usually costs $300–$500 and can save tens of thousands by catching state-specific issues, basis tracking, AMT credit projections.
Don’t exercise more than you can lose. If a 100% drop in the stock price would create a debt you can’t service, you’re exercising too much. The break-even-sale-price output is the diagnostic — if it’s above your honest estimate of where the stock will trade, you’re underwater on a paper basis, and need cash to survive that.

Open the ISO Exercise + AMT Calculator → and run your specific shares, strike, and FMV. Pair with the Tech TC Breakdown calculator to see how ISOs fit into your overall comp, and the RSU Vesting + Cliff Trap tool if you also have RSU grants whose vesting affects your other-income line in this calculation.