Leaving a Startup? Your Option and ISO Tax Deadlines May Not Match

After leaving a startup, you generally keep only the options vested through your final service date, and you can exercise them only while the governing documents permit. If the grant is an incentive stock option, a separate federal employment test determines whether an exercise retains ISO tax treatment.

Do not treat “90 days” as a universal deadline or assume it matches three calendar months. Carta’s departure guidance notes that many companies use a 90-day post-termination exercise period, while some equity plans or separation agreements provide longer windows. Your contractual right to exercise and your eligibility for ISO treatment can therefore end on different dates.

Put the two deadlines on separate lines

The contractual exercise deadline determines whether the company will accept your purchase. Find the termination provision in the equity plan, grant notice, option agreement and any signed separation agreement. Record the official termination date, the final exercise date, the grant’s original expiration date and what must be delivered before the cutoff.

The federal ISO window concerns tax classification, not whether the option contract remains open. IRS Publication 525 generally requires employment from the grant date through the date three months before exercise, with a one-year period for an employee who is disabled; failure to meet the employment requirement causes the option to be treated as nonstatutory.

A plan can permit exercise after the federal window closes, but contractual permission does not preserve ISO treatment. Conversely, meeting the federal employment test does not help if the option has already expired under the plan. Ask the company to confirm its contractual cutoff in writing, and have a qualified tax adviser calculate the federal date from your actual termination and exercise facts.

Collect the controlling documents before access disappears

Download the complete equity file while you can still reach the company’s portal. A dashboard summary may omit definitions, amendments or special termination provisions. A Fidelity overview of stock options explains that unvested options are generally forfeited at departure, while vested grants commonly have a limited post-employment exercise window that must be checked in the grant contract.

Your departure file should contain:

• the equity incentive plan, grant notice and option agreement for every grant;
• each grant’s classification, grant date, strike price, vested quantity and original expiration date;
• the vesting ledger through the official termination date;
• signed amendments, approved extensions and the separation agreement;
• exercise instructions, accepted payment methods and the rule determining when delivery is complete;
• the latest fair market value supplied by the company and its valuation date;
• terms covering repurchase rights, rights of first refusal and transfer restrictions.

Reconcile the vested quantity and option classification with the plan administrator. If an extension is part of the departure package, confirm that it was formally approved and incorporated into the controlling documents rather than relying on an informal conversation or unsigned proposal.

Price the purchase and tax exposure together

Start with the exercise payment: the number of options exercised multiplied by the strike price. Model each grant separately because an exercise retaining ISO treatment and an exercise taxed under nonstatutory rules can produce different timing and character of income.

For an ISO exercise, the federal AMT adjustment can equal the fair market value of the shares over the option price when the shares become transferable or are no longer subject to a substantial risk of forfeiture. No AMT adjustment is required under the rule described above if the shares are disposed of in the same year as the exercise, but that disposition can have other tax consequences.

Consider a clearly hypothetical grant of 20,000 vested options with a $1 strike price. Exercising all of them costs $20,000. If the fair market value at exercise is $4 per share, the hypothetical spread is $60,000, which may enter the AMT calculation even though the holder has sold no shares and received no cash.

Compare at least three scenarios: no exercise, a partial exercise and exercise of all vested options. For each, estimate the purchase payment, regular federal and state tax, possible AMT, cash remaining afterward and the amount you could afford to lose if the shares never become liquid. A partial exercise reduces the capital committed, but it does not extend the deadline for options left unexercised.

Treat the resulting shares as illiquid

Exercising replaces an option with shares; it does not produce a buyer. SEC guidance on private secondary markets explains that securities issued by startups through exempt offerings are often illiquid, privately held securities may not be freely traded and certain securities acquired through employee benefit plans can be restricted.

Ask whether the company permits employee-initiated secondary sales, has conducted tender offers and applies a right of first refusal or other transfer approval. Those facts can clarify possible sale routes, but none guarantees future liquidity. A preferred-stock financing price also does not establish that employee common shares can be sold at the same price—or sold at all.

The decision is therefore not simply whether fair market value exceeds the strike price. It is whether an uncertain, concentrated private holding justifies the purchase payment and possible tax bill within your own cash constraints.

Complete the exercise and preserve the record

Once you decide, follow the prescribed exercise procedure exactly. Confirm whether the company must receive a signed notice, cleared funds or both by the deadline; initiating a transfer on the final day may be insufficient if the documents require receipt. Request written confirmation of the effective exercise date, grant classification, number of options exercised, price paid and shares issued.

Retain the plan and grant documents, exercise notice, payment proof, ownership statement, fair market value used at exercise and related tax forms. For an ISO exercise, keep Form 3921 or the corresponding statement and maintain separate regular-tax and AMT basis records while holding the shares.

Your departure-day sequence is to establish the vested quantity, identify the contractual expiration, calculate the separate ISO cutoff, model purchase cost and taxes, assess liquidity and then complete the required exercise steps. The deadline that matters depends on what you are trying to preserve: the contractual right to buy, ISO tax treatment or both.

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