Startup Equity Basics: ISOs, NSOs, RSUs, and How to Value Them

Startup equity is simultaneously the most exciting and the most misunderstood part of a tech compensation package. Candidates routinely accept offers with six-figure option grants they don't understand, and just as routinely, those grants expire worthless or get diluted into irrelevance. Before you sign anything, you need to understand what you're actually being offered—because the company's recruiter is not going to explain the downside scenarios. This guide does.

We'll cover the three main equity instruments you'll encounter—Incentive Stock Options (ISOs), Non-Qualified Stock Options (NSOs), and Restricted Stock Units (RSUs)—how each is taxed, and how to build an honest valuation framework that accounts for the real probability that most startups fail. None of this is legal or tax advice. It is, however, the honest conversation you deserve to have before your next offer call.

ISOs, NSOs, and RSUs Are Not the Same Thing

These three instruments are structurally different, and confusing them will cost you money.

Incentive Stock Options (ISOs) are the most tax-advantaged instrument and are available only to employees (not contractors or advisors). You receive the right to purchase shares at a fixed strike price—the Fair Market Value (FMV) on the grant date, set by a 409A valuation. You pay nothing upfront. ISOs can qualify for long-term capital gains treatment if you hold the shares long enough, which is the main reason people get excited about them.

Non-Qualified Stock Options (NSOs) work similarly on the surface—you get a strike price, you exercise at some point, you buy shares—but the tax treatment is worse. The spread between your strike price and the FMV at exercise is taxed as ordinary income the moment you exercise, regardless of whether you've sold a single share. NSOs can be granted to employees, contractors, board members, and advisors.

Restricted Stock Units (RSUs) are not options at all. You don't buy anything. Shares (or the cash equivalent) are granted to you and vest over time. When they vest, you own shares—and the FMV at vesting is taxed as ordinary income immediately. RSUs are more common at late-stage startups and public companies because they have straightforward value: if the stock is worth $20/share and 1,000 RSUs vest, you have $20,000 of income. No strike price math required.

"An ISO at a $10 strike price sounds great until you realize the 409A FMV is also $10 and the company needs a 10x outcome just to make your options worth exercising."

The key practical difference: with options (ISOs and NSOs), you need the stock price to exceed your strike price before you make any money. With RSUs, you make money as long as the stock is worth anything at all when it vests.

The Tax Trap That Catches Everyone Off Guard

Equity taxation is where most people get burned. Here is the honest breakdown:

ISOs — the tax rules:

1. No tax at grant.
2. No regular income tax at exercise—but the spread is an AMT (Alternative Minimum Tax) preference item. If you exercise a large ISO grant in a year when the spread is substantial, you may owe AMT even if you never sell a share.
3. If you hold shares for at least 2 years from grant date AND 1 year from exercise date, you pay long-term capital gains rates on the full gain at sale. In 2026, that's 0%, 15%, or 20% depending on your income.
4. If you don't meet those holding periods (a "disqualifying disposition"), the spread at exercise is taxed as ordinary income.

NSOs — the tax rules:

1. No tax at grant.
2. At exercise, the spread (FMV minus strike price) is ordinary income—up to 37% federal, plus state, plus FICA in some cases.
3. After exercise, any additional appreciation is a capital gain, short- or long-term depending on hold time.

RSUs — the tax rules:

1. No tax at grant.
2. At vesting, the full FMV of vested shares is ordinary income. Period.
3. After vesting, any additional appreciation is a capital gain.

The practical danger zone is early exercise of ISOs at a pre-revenue startup. You exercise when the 409A FMV is $0.10/share and the strike price is $0.10/share—zero spread, potentially zero AMT, you start your holding clock. Smart move if the company succeeds. But if the company raises a Series B and the 409A jumps to $3.00/share before you exercise, you now have a $2.90/share AMT exposure on paper gains in illiquid shares. That has bankrupted real people.

How to Actually Value Your Equity (Stop Using the Company's Numbers)

Every founder will tell you their option grant is worth $X based on the current 409A times the number of shares. This number is almost certainly misleading. Here is a more honest approach.

Step 1: Find out what you actually own. Ask for the fully diluted cap table or, at minimum, the total fully diluted share count. Divide your shares by that number to get your ownership percentage. A grant of 100,000 shares sounds impressive until you learn there are 200 million fully diluted shares outstanding—that's 0.05%.

Step 2: Apply a realistic exit multiple. Look up comparable exits in the company's sector. Most venture-backed startups that exit do so between $50M and $200M. A unicorn exit is genuinely rare. Use a range of scenarios—$100M, $300M, $1B—and see what your stake would be worth in each.

Step 3: Account for liquidation preferences. This is the step most candidates skip entirely. Preferred investors almost always have a liquidation preference—meaning they get paid back their investment (sometimes 1x, sometimes 2x, sometimes participating) before common shareholders see a dollar. In a $100M exit, if VCs put in $80M with a 1x preference, common shareholders split $20M. Your options are on common stock. If the company raised $150M and exits at $200M, you may get very little.

Step 4: Discount for probability and illiquidity. A study of venture-backed startups consistently shows that roughly 75% return less than invested capital. Apply that to your math. Your expected value calculation should also discount for the fact that your shares are illiquid—you can't sell them when you want. A 30-50% illiquidity discount is not unreasonable for an early-stage company.

Step 5: Factor in dilution. Every future funding round dilutes your percentage. A seed-stage company that raises a Series A, B, and C might dilute early employees by 40-60% before any exit. Model this in.

Vesting Schedules and Cliff Cliffs—Know What You're Walking Into

The standard vesting schedule is 4-year vesting with a 1-year cliff. This means:

• You vest 0 shares if you leave before month 12.
• At month 12, 25% of your grant vests in one event (the cliff).
• After that, vesting happens monthly (or quarterly) for the remaining 3 years.

This structure exists to align your incentives with the company's long-term success. It also means the company can fire you in month 11 and owe you nothing—which happens. Negotiate for accelerated vesting provisions if you have leverage.

Single trigger acceleration means some or all of your unvested shares vest automatically upon acquisition, regardless of what happens to your role.

Double trigger acceleration requires both an acquisition AND a change in your role (termination or demotion) for unvested shares to accelerate. This is more common and less generous to employees.

Also check your post-termination exercise window. Standard early-stage option grants give you 90 days after leaving to exercise your vested options. Miss that window, your options expire. Some companies have extended this to 5 or 10 years, which is significantly more employee-friendly—and a real differentiator worth asking about.

The Questions You Must Ask Before Signing

Do not accept any equity offer without getting clear answers to all of these:

1. What is the total fully diluted share count, including all option pools?
2. What is the current 409A FMV per share, and when was the last 409A completed?
3. What is the total venture capital raised to date, and what are the liquidation preferences on each round?
4. What is the option pool size, and is a refresh planned before the next funding round (which would dilute me further)?
5. What is the post-termination exercise window for vested options?
6. Is there a single or double trigger acceleration clause in the option agreement?
7. Has the board approved any secondary transactions, and is there any liquidity pathway before an IPO or acquisition?

If the company refuses to answer any of these, that tells you something important about how they treat employees.

RSUs at Late-Stage Startups: Not as Simple as They Look

As startups mature, many shift from options to RSUs. RSUs are simpler to understand—you get shares, they vest, you own them—but late-stage RSUs come with their own complications.

The biggest issue: tax at vesting on illiquid shares. At a public company, you can sell shares to cover the tax bill the day your RSUs vest. At a private company, you can't. If 1,000 RSUs vest and the 409A says each share is worth $50, you have $50,000 of ordinary income—and a tax bill of perhaps $18,000–$22,000 depending on your bracket and location. But you can't sell shares to pay it. You either need cash on hand or you need the company to offer a sell-to-cover program (some do, most early-stage ones don't).

Late-stage RSU grants also tend to have double-trigger vesting: shares only vest when both (a) your time-based schedule is met AND (b) a liquidity event occurs. This protects you from the tax problem above but means your equity is worthless if the IPO never happens or gets delayed indefinitely. In 2026, with the IPO market having been selective for several years, this is a real risk—not a hypothetical one.

Common Mistakes Engineers Make With Startup Equity

• Treating the grant value in the offer letter as real money. It's a projection based on a 409A that may be outdated and an exit that hasn't happened.
• Not early exercising ISOs when the 409A is low. If you're joining pre-Series A and the strike price is $0.01/share, exercising immediately costs almost nothing and starts your long-term capital gains clock.
• Forgetting the 90-day exercise window. People leave jobs and forget they have a quarter to exercise. Vested options worth $50,000 have expired because someone missed the deadline.
• Ignoring liquidation preferences. A $500M acquisition can still result in zero payout to common shareholders if the company raised $400M at 2x participating preferred.
• Not negotiating the post-termination window. This is more negotiable than candidates think, especially at the senior level.
• Assuming the next round won't dilute you significantly. Model in 20-25% dilution per round. Early employees at companies that raised five rounds are often surprised how small their final stake is.

"The only equity worth having is equity you understand. If you can't explain your cap table position to a friend, you're flying blind."

Next Steps

Here are five concrete actions you can take this week to get a handle on your equity situation—whether you're evaluating a new offer or auditing what you already hold:

1. Pull your current option agreement and find three numbers: your strike price, the total fully diluted share count, and the current 409A FMV. Calculate your actual ownership percentage. If you don't have these numbers, email your stock plan administrator today.
2. Model three exit scenarios using a simple spreadsheet: a modest exit (1-2x the last valuation), a solid exit (3-5x), and a big win (10x+). Apply the liquidation preference stack to each scenario and see what common shareholders actually receive.
3. Check your post-termination exercise window. Open your option grant agreement and find the exact language. If it's 90 days, decide now whether you'd exercise immediately upon leaving—because you won't have time to think about it when you're actually in that situation.
4. Talk to a CPA who specializes in equity compensation. If you have more than $50,000 in option value (even on paper), the cost of a one-hour consultation ($200-$400) is trivially worth it for AMT planning alone. Don't use your regular tax preparer who files W-2s—find someone who does equity comp regularly.
5. If you're evaluating a new offer, ask all seven questions listed in the section above before signing. Put them in an email. Serious companies will answer. Evasive answers are data.

Related guides

• Tender Offers for Startup Equity in 2026 — What They Are and How to Evaluate Them — A startup tender offer can turn private equity into cash, but the details decide whether selling is smart, premature, or risky. This guide explains how 2026 tender offers work, what documents and tax questions to review, and how to decide how much equity to sell.
• Secondary Markets for Startup Equity in 2026 — Forge, EquityZen, and What's Actually Liquid — Secondary markets can turn private-company stock into cash, but only when transfer restrictions, company approvals, buyer demand, tax treatment, and platform process all line up. This guide explains how Forge, EquityZen, tender offers, private brokers, and company-led programs work — and how employees should decide whether liquidity is real.
• Sabbatical Policies in Tech in 2026 — Who Offers Them and How to Plan Around One — Sabbatical policies in tech in 2026 range from formal paid breaks after tenure milestones to informal unpaid leave that depends entirely on manager support. This guide explains who tends to offer sabbaticals, how to plan one, and how not to damage your role, equity, or promotion path.
• 401(k) match norms in tech in 2026 — by company size and stage — A guide to 401(k) match norms across tech companies in 2026, including startup vs public-company patterns, vesting schedules, true match value, mega backdoor Roth availability, and offer-stage questions.
• The 83(b) Election in 2026 — When to File, Deadlines, and What Happens if You Miss It — The 83(b) election can save startup employees and founders from painful vesting-date taxes, but the 30-day deadline is unforgiving. Here is when it applies, how to file, and what to do if you miss it.