Stock option net after-tax value.

What employee stock options actually are

Employee stock options give you the right to buy company shares at a fixed price (the strike price) after a vesting period. If the stock rises above the strike, exercising produces immediate profit. If the stock falls below, the options are worthless until (or unless) the stock recovers. Options are concentrated risk — your career and your investment are both tied to the same company — but with significant upside for employees of companies that succeed. This calculator estimates the potential value; the commentary below covers the non-obvious considerations.

The vesting schedule that determines availability

Most employee stock options vest over 4 years with a 1-year "cliff":

Year 1: Nothing vested. If you leave in year 1, you keep nothing.

Month 12: 25% vests suddenly (the cliff). You now have the right to exercise 25% of your grant.

Months 13-48: 1/48th of the grant vests each month (monthly vesting after the cliff).

Month 48: 100% fully vested.

Variations exist: 3-year vesting, immediate vesting, back-loaded vesting (more vests later), or performance-based vesting. Check your specific grant document. The vesting schedule creates a retention effect — leaving mid-vest means leaving unvested shares behind.

The exercise timing decision

Once vested, you can exercise at any time (while still employed, plus a post-termination exercise window). Key considerations:

Current value vs future expectation. Exercising locks in current gain. If you believe the stock will rise further, waiting captures the additional gain (but risks price drops).

Tax implications. Exercising options usually triggers income tax on the gain (share price minus strike price times shares) unless you're in an the tax authority-approved scheme (EMI, CSOP, SAYE). For an unapproved scheme, a 50,000 exercise gain costs 40%+ in tax and NI.

Cash requirement. Exercising requires paying the strike price in cash. For significant grants, this can be 10,000s of upfront cash.

Diversification risk. Holding both your job and your investment with the same company doubles concentration risk. Exercising and selling diversifies.

Tax treatment by scheme type

Employee stock option schemes fall into categories:

EMI (Enterprise Management Incentive): Approved scheme for small/medium companies. Exercise is CGT-only (10-24%), not income tax. Single largest tax-efficient option structure available; heavily used by startups for employee grants.

CSOP (Company Share Option Plan): Approved scheme with lifetime limit of 60,000 per grant. Tax-free exercise if held 3+ years after grant. Used by larger companies for executives.

SAYE (Save As You Earn): 3 or 5-year saving scheme with tax-free exercise at the end. Low maximum (500/month). Popular with plcs.

Unapproved schemes: Exercise gain taxed as income at marginal rate plus NI. Usually 42-47% total tax on the gain for higher earners. Most disadvantageous but also most flexible for companies.

EMI vs unapproved treatment on the same 100,000 gain: EMI pays 16,800 (assuming 18% CGT with annual allowance used); unapproved pays 42,000-47,000. A 25,000-30,000 tax difference on the same economic outcome — a significant reason to check your scheme type early.

The 409A/valuation problem

Private company stock options have strike prices set based on current company valuation (409A; equivalent is the tax authority-approved valuations). The strike price typically reflects "fair market value" at grant — but for early-stage startups, this can be wildly lower than public market equivalents. A startup at 50M valuation with 10M shares has a strike around 5/share. If the company IPOs at 500M, the shares are worth 50 each — a 10× return on the strike price. This leverage is why startup equity grants can produce exceptional outcomes (and also why they're worthless if the company fails).

The 90-day post-termination window

Most option schemes require you to exercise vested options within 90 days of leaving the company. If you miss this window, vested options expire. This creates a specific problem: you may have 50,000 of "on paper" gains in vested options but need to pay 20,000 cash to exercise them, and you're not working. Many employees lose vested options because they can't fund the exercise in the 90-day window. Some schemes offer extended exercise windows (1 year, 5 years, or longer) — significantly better for employees but less common. Check your scheme's post-termination provisions before leaving.

The "cash-flow" exercise trap

A common pattern: employee has 100,000 of vested unapproved options. Exercise requires 20,000 strike price payment plus 40,000 immediate income tax and NI. The employee needs 60,000 cash to exercise. This is why many employees can't actually realize the paper value of their options — the tax-plus-strike cost is prohibitive. Solutions: cash-less exercise (sell some shares immediately to cover costs), exercise in small tranches over time (if scheme permits), or wait until cash is available. This constraint is most severe for pre-IPO employees whose shares aren't freely sellable.

Diversification advice ignored by most option-holders

Standard financial planning: don't have more than 10-15% of your wealth in any single stock. This is why investment funds and diversified portfolios are mathematically superior. Employee option holders systematically violate this: their career and their investment portfolio are both concentrated in their employer. If the company falls, they lose both wealth and employment simultaneously. The rational action is to exercise and diversify as quickly as tax and scheme rules allow. The emotional action is to hold, betting on continued company success. Most employees overweight the emotional argument.

When holding is the right call

Despite diversification arguments, some scenarios favor holding:

EMI scheme with substantial time until IPO/sale (tax deferral until sale; no CGT if held 2 years).
Very high conviction in company (public company with multi-year growth trajectory).
Early vesting of small portion (holding the small vested portion to see how company develops is rational).
Unapproved scheme near IPO (IPO typically happens at higher valuation; waiting captures more upside).

These scenarios share a common feature: the potential additional upside exceeds the diversification cost. Most other situations don't meet this bar.

The mental accounting mistake

Employees often treat "paper value" of options as real wealth — counting it in household net worth, making lifestyle decisions based on it. This is a mental accounting error. Options are worth what they're worth today at current prices, minus the cost and risk of exercising. A 300,000 paper gain that's never exercised is worth zero; a 50,000 paper gain that's exercised and diversified is worth 50,000. Treat option paper value as contingent wealth, not banked wealth, until it's actually in your brokerage account.

What this calculator shows

The tool computes the potential value of stock options based on strike price, vesting schedule, and current/projected share price. It doesn't automatically model tax scheme type, exercise timing strategy, or diversification implications. Use the figure as the potential-value estimate; evaluate actual exercise decisions against tax treatment, cash requirements, and concentration risk.