Stock options are the most misunderstood part of a startup offer letter — and the most consequential if you get the details wrong.
Most employees read "100,000 options" and stop there. They don't ask: options at what strike price? Vesting on what schedule? ISOs or NSOs? What happens if I leave in 18 months? These aren't edge cases. They determine whether your equity is worth exercising at all.
After 65+ investments and three startups, I've watched equity that should have been transformative quietly evaporate because employees didn't understand the mechanics. Here is the complete breakdown.
The Anatomy of a Startup Stock Option Grant
When a startup grants you stock options, you receive the right to purchase a specific number of shares at a fixed price — the strike price — at any point after they vest. You are not given shares. You are given the option to buy them later, at today's price.
Strike Price
The price per share you can buy at. Set by a 409A independent appraisal at grant time. Common stock is typically priced at 10–30% of the preferred stock valuation.
Vesting Schedule
The timeline over which you earn the right to exercise. Standard: 4 years with a 1-year cliff. Some companies use 3-year vesting or monthly vesting from day one.
Cliff
The minimum tenure required before any options vest. Standard cliff is 12 months — if you leave before your first anniversary, you forfeit everything.
Exercise
The act of paying the strike price to convert your options into actual shares. You can only exercise vested options. Exercising has tax consequences.
Grant Date
The date your options are officially issued. Your strike price is locked to the 409A valuation on or near this date.
Option Pool
The total number of shares reserved for employee equity. Typically 10–20% of a startup's fully diluted share count, which gets replenished as the company raises.
How Vesting and the Cliff Actually Work
The 4-year / 1-year cliff is the market standard. Here is what the timeline looks like on a grant of 48,000 options:
| Month | Event | Cumulative Vested Options |
|---|---|---|
| Month 0 | Grant date | 0 |
| Month 11 | One day before cliff | 0 — leave now, forfeit all |
| Month 12 | 1-year cliff | 12,000 (25%) |
| Month 13 | Monthly vesting begins | 13,000 |
| Month 24 | 2-year mark | 24,000 (50%) |
| Month 36 | 3-year mark | 36,000 (75%) |
| Month 48 | Fully vested | 48,000 (100%) |
Monthly vesting after the cliff is calculated as 1/48 of the total grant per month (for a 4-year schedule). Some companies vest quarterly instead of monthly, which means you earn nothing between milestones.
ISOs vs NSOs: The Tax Difference Founders Don't Explain
Most early employees receive Incentive Stock Options (ISOs). Contractors, advisors, and sometimes later-stage hires receive Non-Qualified Stock Options (NSOs). The distinction matters enormously at tax time.
Incentive Stock Options (ISOs)
- ✓ Only available to W-2 employees
- ✓ No ordinary income tax at exercise
- ✓ Long-term capital gains if held 1+ year post-exercise and 2+ years post-grant
- ✓ Maximum federal capital gains rate: 20%
- ⚠ AMT (Alternative Minimum Tax) can apply to the spread at exercise
- ⚠ Annual ISO exercise limit: $100K at fair market value
Non-Qualified Stock Options (NSOs)
- ✓ Can be granted to employees, contractors, advisors, directors
- ✓ No annual limit on grant size
- ✓ Simpler tax reporting — no AMT concerns at exercise
- ✗ The spread at exercise is taxed as ordinary income (up to 37% federal + state)
- ✗ Employer must withhold payroll taxes
- ✗ Higher tax bill on the same dollar of gain versus ISOs
The 90-Day Exercise Window: The Trap Most Employees Miss
Standard option agreements give you 90 days after your last day of employment to exercise vested options. After that window closes, the options expire — worthless.
This creates a brutal decision for employees who leave before a liquidity event. To exercise, you need to pay the strike price in cash — sometimes tens or hundreds of thousands of dollars — for shares in a company that is illiquid and may never generate a return. Most people can't or won't write that check.
Example: The $180K exercise decision
Options granted: 60,000 shares at $3.00 strike (409A at grant)
Current 409A: $6.00 (company raised Series B at $30/share preferred)
Vested options: 45,000 after 3 years
Exercise cost: 45,000 × $3.00 = $135,000 out of pocket
Plus potential AMT on the $135,000 spread ($6 - $3 × 45,000)
Outcome: uncertain — company may exit at $30/share or may never exit
Some employee-friendly companies have extended exercise windows to 5 or 10 years after departure — Stripe, Coinbase, and Pinterest have done versions of this. When evaluating an offer, it's worth asking. Most companies won't volunteer the information.
How to Value What You're Actually Being Offered
Raw option counts are meaningless without context. Here is the framework for evaluating what a grant is actually worth:
Ask how many total shares exist (including all outstanding options, warrants, and convertible notes). Your percentage ownership is your grant divided by that number.
If you're getting 100,000 shares and the fully diluted count is 10 million, you own 1% — before any future dilution from new investors or option pool refreshes.
Look at comparable exits in your space. If the company last raised at a $50M valuation and similar companies sell for 3–5x revenue, model a range of outcomes. Your 1% is worth $500K in a $50M exit, $5M in a $500M exit.
Each new funding round typically dilutes existing shareholders by 20–25%. A company going from Seed to Series C will likely dilute early employees by 50–60% before exit.
Don't forget you still have to pay the strike price to convert options to shares. Factor in the tax bill too, especially for NSOs.
Track your equity ownership alongside company funding milestones on the Benchmarking Dashboard. If you're a New York-based employee, the NY QSBS dashboard covers whether your shares qualify for Section 1202 exclusions.
Early Exercise and the 83(b) Election
Some companies allow employees to early exercise — purchasing unvested shares before they vest, typically right after joining. This is only worth doing if the 409A strike price is very low (near-zero at founding) and you believe in the company's trajectory.
If you early exercise, you must file an 83(b) election with the IRS within 30 days of the exercise. This locks in your tax basis at the current (low) value — meaning you won't owe ordinary income tax on the future appreciation as shares vest. Miss the 30-day window and you pay ordinary income tax on the fair market value of shares as they vest, which can be catastrophic if the stock price has risen.
83(b) election rules
- • Must be filed within 30 calendar days of exercise — no exceptions
- • File with the IRS service center where you file your tax return
- • Send a copy to your employer for their records
- • Only makes sense if the spread between strike price and 409A is small (<$10K)
- • Does not apply to vested options — only unvested shares purchased early
The best equity package in the world is worthless if you don't understand the terms.
Read your option agreement before you sign it. Ask about the 90-day window. Ask about the fully diluted count. The answers tell you what the company actually thinks your equity is worth.
For startup equity and cap table benchmarking, visit the Benchmarking Dashboard at Value Add VC. Originally published in the Trace Cohen newsletter.