Understanding Stock Option Pools: Setup, Size, and Dilution

A stock option pool is the equity you set aside for future employees, advisors, and key hires. It is one of the most powerful tools a startup has for recruiting talent — but it is also one of the most misunderstood. Get the pool size wrong, and you either dilute founders unnecessarily or run out of equity to offer competitive packages. This guide walks through how option pools work, how to size them intelligently, how they interact with fundraising, and the practical mechanics of granting options to employees.

What is a stock option pool?

A stock option pool is a block of shares reserved by the company for future issuance to employees, advisors, and other service providers. The shares in the pool are not issued immediately — they are "set aside" so the company can grant options to individuals over time without needing shareholder approval for each grant.

When someone receives a stock option, they get the right (but not the obligation) to buy shares at a predetermined price (the "exercise price" or "strike price") at some point in the future, usually after a vesting period. If the company's value increases, the difference between the exercise price and the current value represents the option holder's gain.

How option pools appear on a cap table

On a cap table, the option pool is typically shown as a single line item with sub-categories:

• Total pool: the total number of shares reserved for the option pool.
• Granted (unvested): options that have been issued to individuals but have not yet fully vested.
• Granted (vested): options that have vested but have not been exercised.
• Exercised: options that have been converted into actual shares (these move out of the "pool" and become issued shares).
• Available: the remainder — shares still in the pool that can be granted to future hires.

Investors typically look at the "available" pool to assess whether the company has enough equity left to hire the team needed to reach the next milestone without needing to expand the pool (which would cause additional dilution).

How to size your option pool

There is no universal formula, but there are practical guidelines based on stage and hiring plan:

The hiring plan approach (recommended)

Instead of picking a percentage arbitrarily, build a bottoms-up hiring plan. List every role you plan to hire before the next funding round, assign an equity range per role based on market data, and total it up. Add a small buffer (10–15%) for unexpected hires or retention grants. This gives you a defensible pool size that you can present to investors with confidence.

The pre-money vs post-money pool debate

This is one of the most consequential details in a term sheet, and many first-time founders miss it:

Practical advice: If an investor insists on a pre-money pool, negotiate the pool size based on your actual hiring plan rather than accepting an arbitrary percentage. A 20% pool when you only need 12% costs founders equity they did not need to give up.

Vesting schedules and exercise mechanics

When you grant options, you need to define the vesting schedule — the timeline over which the option holder earns the right to exercise their options:

• Standard 4-year vesting with 1-year cliff: the most common schedule. Nothing vests during the first year. After 12 months, 25% vests at once (the "cliff"). The remaining 75% vests monthly or quarterly over the next 3 years.
• Exercise price: typically set at the fair market value of the shares at the time of the grant. In the US, this requires a 409A valuation. In the UK (EMI), the exercise price is agreed with HMRC.
• Exercise window: after vesting, the option holder can buy the shares. If they leave the company, they usually have a limited time (often 90 days) to exercise vested options or lose them. Some companies now offer extended exercise windows (1–10 years) to be more employee-friendly.

UK EMI options vs US ISO/NSO options

The tax treatment of options varies significantly between the UK and US:

Common option pool mistakes to avoid

• Creating a pool that is too large: Founders often accept investor demands for a 20% pool without pushing back. Size the pool based on your hiring plan, not investor convenience.
• Granting options without board approval: Every option grant should be documented with a board resolution. Verbal promises of equity are dangerous and unenforceable.
• Not setting the exercise price correctly: In the US, you need a 409A valuation. In the UK, you need HMRC agreement for EMI. Getting this wrong creates tax liability for the option holder.
• Forgetting the cliff: Without a cliff, an employee who leaves after 2 months has vested options. A 1-year cliff protects the company and aligns incentives.
• No documentation: Every grant needs a signed option agreement, a board resolution, and an update to the cap table. If any of these are missing, the grant may not be enforceable.

How eSignHub helps manage option pools

eSignHub's equity management tools let you track your option pool alongside your cap table. You can create option grants, set vesting schedules, track exercised options, and send option agreements for e-signature — all in one workflow. When you grant options, eSignHub records the board resolution, the option agreement signature, and the cap table update together, so your records are always in sync.