Startup Stock Options Explained: Option Pool Size, ISO vs NSO and Grants for Founders (2026)

Startup stock options are the right to buy a set number of company shares at a fixed price, the strike price, once they vest. Founders grant them from an option pool, which is a block of shares reserved for the team. At seed, the median pool on Carta was 11.8% of the company after the round closed (Carta, 2025).

TL;DR: Most early-stage startups reserve 10% to 15% of fully diluted shares for the option pool (CRV, 2026), and pools grow toward about 20% by later stages (Carta, 2024). Investors usually want the pool created before their money comes in, so the dilution falls on founders. Give employees ISOs and contractors or advisors NSOs. The median first hire gets 1.4% to 1.5% of the company (Carta, 2025), vesting over four years with a one-year cliff.

This guide explains US rules for founders. It is not tax or legal advice: have a startup lawyer set up your equity plan and ask a tax advisor about individual cases.

How Do Startup Stock Options Work?

A stock option is a contract that lets the holder buy shares later at today's price. The strike price must be at least the fair market value of the stock on the grant date, which private companies set with a 409A valuation (Carta, 2026). If the company grows, the shares become worth more than the strike price, and that gap is the employee's gain.

The life of a grant has four steps:

1. Grant. The board approves a number of options at a strike price. Nothing is owned yet.
2. Vesting. The employee earns the right to exercise over time. The most common schedule is four years with a one-year cliff (same source).
3. Exercise. The employee pays the strike price to turn vested options into real shares. This is where taxes can start.
4. Liquidity. The shares turn into cash only through an acquisition, an IPO or an approved secondary sale. Until then they are hard to sell.

Here is a simple example. An engineer receives 20,000 options at a $0.50 strike price. Four years later, a buyer pays $5.00 per common share. She pays $10,000 to exercise and receives shares worth $100,000, a $90,000 gain before taxes. If the buyer pays $0.40 per share instead, the options are worth nothing.

What Is an Option Pool?

An option pool is a block of shares a company sets aside to grant equity to employees, advisors and other service providers. The shares are not issued yet: they move to people only when options are granted and later exercised. The board authorizes the pool, and stockholders approve the equity incentive plan (Carta, 2026).

You will also hear it called an employee stock option pool, an employee option pool or an ESOP. The pool counts in the "fully diluted" share count, so every investor will ask how big it is and who pays for it. It covers more than new hires: CRV notes that a meaningful share of the first pool goes to retention and refresh grants (CRV, 2026), and some goes to advisors. If you are granting equity to advisors, our guide to advisory shares and the FAST agreement covers the usual ranges.

How Big Should an Option Pool Be?

Most early-stage startups reserve 10% to 15% of fully diluted shares, and 10% is a common figure at seed (CRV, 2026). Carta data shows pre-seed pools typically start at 10%, then grow by 1 to 1.5 points per round until a US tech startup reserves about 20% for employees (Carta, 2024).

These figures come from different data cuts and years, so read them as ranges, not targets. The better method is bottom-up. List the hires you plan before your next round and give each role a grant from the benchmarks below. Add refresh grants and a buffer, then check the total against the 10% rule of thumb (Carta, 2026). Carta suggests sizing the pool for about two years of hiring, and notes that companies typically use 60% to 70% of it before the next raise (Carta, 2025).

What if a seed investor asks for 20%? Carta calls that "almost always too large a reserve for a company at this stage" and suggests pushing back (Carta, 2024). A hiring plan is your best argument.

How Does the Option Pool Dilute Founders?

The option pool dilutes founders most when it is created or expanded inside the pre-money valuation, which is what many VC term sheets ask for (Carta, 2026). The same guide reports that in 71% of cases, the term sheet created a pool or topped up the existing one. The new investor is usually not diluted by that expansion: existing holders are (Carta, 2025).

This is the option pool shuffle. It makes the headline pre-money valuation look higher than what the founders really get.

Worked example. Two founders own 100% of a startup. They raise $3 million at a $12 million pre-money valuation, so the post-money is $15 million and the investor owns $3M / $15M = 20%. The term sheet asks for a 15% option pool after the round.

• Pool in the pre-money (the usual term sheet). The pool is carved out before the investor buys in. After the round: investor 20%, pool 15%, founders 65%. The founders' stake is worth 65% x $15M = $9.75M, so their "effective" pre-money is $9.75 million, not $12 million.
• Pool in the post-money. The investor buys 20%, then the pool is created and dilutes everyone. After the round: founders 80% x 0.85 = 68%, investor 20% x 0.85 = 17%, pool 15%.

Same round, same pool size, and the founders keep 3 more points of the company when the pool sits in the post-money. That is why investors prefer the first version.

SAFEs make it worse, and most pre-seed rounds are raised on them. Carta points out that SAFE holders convert in the priced round without being diluted by the new pool, so the founders absorb even more (Carta, 2025). You can model your own round in the dilution calculator, and our startup equity dilution guide follows one founder through every round. For the clause itself, see how to read a VC term sheet.

How do you push back? CRV suggests asking for a post-money pool or justifying a smaller pool with a detailed hiring plan (CRV, 2026). Carta adds that the pool is one term in a wider trade-off with round size and valuation, so a bigger pool can be the price of a higher headline number (Carta, 2025).

ISO vs NSO: What Is the Difference?

ISOs (incentive stock options) can only go to employees and can get capital gains treatment, while NSOs (non-qualified stock options) can go to almost anyone and are taxed as ordinary income when exercised. An ISO holder owes no regular income tax at exercise, but the spread counts for the alternative minimum tax (AMT) (IRS Topic 427, 2026).

Sources: IRS Topic 427 (2026), IRC §422, Cooley GO (2025), Carta on ISOs (2026), Carta on NSOs (2026).

For a founder, the choice is mostly made for you. Employees get ISOs because the tax deal is better for them. Contractors, advisors and outside directors get NSOs because they cannot legally receive ISOs. One plan can issue both. For ISOs to qualify, stockholders have to approve the plan within 12 months before or after the board adopts it (IRC §422(b)(1)). Set the plan up properly from day one.

The ISO advantage has limits. If an employee sells before the holding periods end, the sale is a "disqualifying disposition" and the spread becomes ordinary income (Carta, 2026). A large exercise can also trigger AMT in a year with no cash to pay it. And a big grant to a senior hire can cross the $100,000 limit, so part of it becomes NSOs automatically.

Early exercise and the 83(b) election

Some plans let employees exercise options before they vest. If the strike price and fair market value are close, the tax bill at exercise stays small. The employee must then file an 83(b) election within 30 days of exercising; without it, tax is due on the spread each time shares vest (Carta, 2023). If the person leaves early, the company can usually buy back unvested shares at the lower of the exercise price or current fair market value (same source). The risk is real: they pay cash for shares that may end up worth nothing.

How Much Equity Should Early Employees Get?

The median first hire at a startup receives 1.4% to 1.5% of fully diluted shares. Grants fall fast after that: by the sixth hire they center around 0.3%, based on more than 9,000 initial grants (Carta, 2025). At the median, the first five hires together use about 3.5% of the company.

The spread around these medians is wide. For first engineers, the 25th percentile was 0.61%, and roughly 70% of first hires are engineers (Carta, 2025). Very large grants are rare: only 7% of the first five hires received 5% or more (Carta, 2024). Grants are also moving up for AI talent: the median initial grant for AI and ML engineers rose 31% between January 2024 and February 2026 (Carta, 2026).

The real trade is salary against equity. Our guide on how to hire your first startup employee covers the usual offers, and how to split equity with your cofounder covers the founder side, which is a different conversation.

How Does Vesting Work for Startup Stock Options?

Vesting is the schedule over which an employee earns the right to exercise. The standard is four years with a one-year cliff, and at least 95% of cliffs fall at the one-year mark (Carta, 2026). With a cliff, 25% vests after the first year and the rest vests monthly over the next 36 months (CRV, 2026).

The cliff protects the company: someone who leaves after five months walks away with nothing, and those options go back to the pool. After the cliff, every month of work adds a slice. Plan refresh grants too, so people who stay keep a reason to stay once their first grant is almost fully vested. Budget for those refreshes when you size the pool.

What Is the Strike Price and How Does the 409A Set It?

The strike price is the fixed price per share an employee pays to exercise. For ISOs, the tax code says it cannot be "less than the fair market value of the stock at the time such option is granted" (IRC §422(b)(4)). Private companies prove that value with a 409A valuation of their common stock (Carta, 2026).

A 409A prices common stock, not the preferred stock investors buy, so it is usually well below your last round's price per share. That gap is good news for employees: a low strike price means more upside. Get the timing right, though. Options granted below fair market value can trigger a 20% penalty tax for the employee under Section 409A (CRV, 2026). Our full guide on what a 409A valuation is explains costs, safe harbor and when a new report is needed, for example right after a funding round.

What Happens to Options When an Employee Leaves?

When an employee leaves, unvested options go back to the pool. Vested options must usually be exercised within a post-termination exercise period, typically 90 days from the last day, or they are forfeited (Carta, 2026). In Q1 2024, 80% of terminated option grants on Carta had the standard 90-day window (Carta, 2024).

Ninety days is short. A departing engineer may need tens of thousands of dollars to exercise, plus tax on the spread for NSOs, for shares she cannot sell. Many simply let them expire. Carta reports that only 33% of in-the-money options were being exercised, down from around 44% before the boom years (Carta, 2024).

Some companies extend the window beyond 90 days: that was the case for the other 20% of terminated grants in the same Carta data. There is a trade-off: ISOs exercised more than three months after leaving lose ISO treatment and are taxed like NSOs (Carta, 2026). Decide your policy before the first departure, write it into the plan, and tell candidates what it is.

Are Startup Stock Options Worth It?

Startup stock options are worth something only if the company is sold or goes public at a price per common share above the strike price, after investors take their liquidation preferences. Many never get there. In an acquisition, options may be converted into the buyer's options, cashed out or canceled, depending on the plan and the deal (Carta, 2026).

The honest picture for a candidate looks like this:

• The company fails. Options are worth zero. Anyone who exercised loses the cash they paid.
• The company sells for less than the preferences. Investors with a liquidation preference get paid first, and common stock can get little or nothing even when the headline price sounds big. Our term sheet guide explains how preferences work.
• The company grows but stays private. Shares are hard to sell. Some companies allow limited secondary sales with approval, or run tender offers, but most restrict sales before an exit (same source).
• The company has a strong exit. Early employees with a low strike price can make a meaningful gain, especially if they exercised early and qualified for long-term capital gains.

So should a candidate take less salary for more options? Only if they can afford the salary cut and see the equity as a long-shot bonus, not as savings. Founders who say this out loud earn more trust than founders who show a spreadsheet with a billion-dollar exit.

Founder Checklist: Setting Up Your First Option Pool

Setting up a pool takes a lawyer, a board vote, a stockholder approval and a 409A, all before your first grant. Use this checklist in order.

1. Adopt an equity incentive plan. You get: a legal plan that can issue ISOs and NSOs. Do this: have your lawyer draft it, the board adopt it, and stockholders approve it within 12 months (IRC §422(b)(1)). You are done when: board and stockholder consents are signed.
2. Size the pool from a hiring plan. You get: a number you can defend to investors. Do this: list hires through the next round, apply the grant benchmarks above, add refreshes and a buffer. You are done when: the total sits in a range you can explain, usually 10% to 15% early on.
3. Get a 409A valuation. You get: a defensible strike price. Do this: hire an independent provider before the first grant. You are done when: the board has adopted the report.
4. Pick option types. You get: the right instrument for each person. Do this: ISOs for employees, NSOs for contractors, advisors and directors. You are done when: every planned grant has a type.
5. Set vesting and exit terms. You get: rules people can rely on. Do this: four years with a one-year cliff, a clear exercise window after leaving, and a decision on early exercise. You are done when: those terms are in the plan and the grant template.
6. Track every grant on a cap table. You get: a fully diluted count investors can trust. Do this: record grants, vesting and exercises in one cap table tool. You are done when: the share count matches your legal documents.
7. Plan the refresh. You get: no surprises at the next round. Do this: expect to top up the pool every 18 to 24 months, usually with the next raise (CRV, 2026). You are done when: the top-up is in your fundraising model.

What to Tell Candidates About Their Stock Options

Tell candidates enough to value the offer themselves. That means the number of options, the percent of fully diluted shares, the strike price, the vesting schedule, the exit window and the option type. A share count alone means nothing without the total shares behind it, and an employee who cannot value a grant cannot weigh it against a higher salary elsewhere.

A clear offer letter, or a short equity summary next to it, covers:

• Options and ownership. "20,000 options, about 0.4% of fully diluted shares today."
• Strike price and the latest 409A. Plus the price per share of your last round, so they see the gap.
• Type. ISO or NSO, and what that means at exercise.
• Vesting. Four years, one-year cliff, monthly after.
• Exit window. 90 days or longer, and whether early exercise is allowed.
• Dilution ahead. Future rounds will shrink their percentage. Be clear that the number is not fixed.
• The honest part. Options can be worth nothing, and you cannot promise an exit.

Candidates compare offers, and the good ones ask hard questions about equity. If you are hiring engineers, our list of startup opportunities for developers shows where they look and what they compare. Answer their questions clearly, in writing, before they have to ask.

Where Startupage Fits

Once your pool is ready, you need people to grant it to. On Startupage you can create a free founder profile, publish open roles as opportunities and browse people who are open to startup jobs. Candidates can also find your role among other startup jobs. Put the equity range in the listing, so candidates can compare it before the first call.

Sources: Carta on the option pool shuffle (2025), Carta on employee option pool size (2024), Carta on 20% seed pools (2024), Carta on option pools by stage (2023), Carta guide to option pools (2026), CRV on structuring the first option pool (2026), IRS Topic 427, Stock options (2026), IRC §422, Cooley GO, ISOs v. NSOs (2025), Carta on how stock options work (2026), Carta on ISOs (2026), Carta on NSOs (2026), Carta on early exercise (2023), Carta on first hire equity (2025), Carta on first engineer equity (2025), Carta on first five hires (2024), Carta on advisor equity (2026), Carta on executive grants (2026), Carta State of Startup Compensation H2 2025 (2026), Carta on the 90-day window (2024), Carta on unexercised options (2024).

Frequently Asked Questions

How big should an option pool be at seed?

Most seed startups reserve 10% to 15% of fully diluted shares, and 10% is common (CRV, 2026). On Carta, the median seed pool was 11.8% after the round closed (Carta, 2025). Size it from a hiring plan covering about two years, and push back if an investor asks for 20% without a reason.

What is the difference between ISO and NSO stock options?

ISOs can go only to employees. They owe no regular income tax at exercise, though the spread counts for AMT, and gains can be long-term capital gains if shares are held 2 years from grant and 1 year from exercise. NSOs can go to anyone and are taxed as ordinary income on the spread at exercise (IRS, 2026).

Who pays for the option pool, founders or investors?

Usually founders. Many term sheets put the pool in the pre-money valuation, so it dilutes existing holders and not the new investor (Carta, 2025). In a $3 million round at a $12 million pre-money with a 15% pool, founders keep 65% with a pre-money pool and 68% with a post-money pool.

How much equity does a first startup employee get?

The median first hire gets 1.4% to 1.5% of fully diluted shares, and by the sixth hire grants center around 0.3% (Carta, 2025). The median first engineer got 1.54% over the past two years (Carta, 2025). Only 7% of the first five hires received 5% or more (Carta, 2024).

How long do you have to exercise options after leaving a startup?

Usually 90 days from your last day, and unexercised vested options are forfeited after that (Carta, 2026). In Q1 2024, 80% of terminated grants on Carta had a 90-day window (Carta, 2024). Some companies offer longer windows, but ISOs exercised more than three months after leaving are taxed as NSOs.

Do startup stock options usually pay off?

Often they do not. Options pay only if the company exits at a price per common share above the strike, after investor preferences. Many startups fail or sell below that point. Even with value on paper, only 33% of in-the-money options were being exercised in 2024 (Carta, 2024).