ISO vs. RSU (Pre-IPO Equity Compensation Guide)
ISOs give employees the right to buy shares later; RSUs promise shares after vesting and settlement. Before an IPO, neither award is cash, and each can create tax or loss risk before you can sell. Compare exercise cost, tax timing, vesting, deadlines, dilution, and liquidity—not headline share counts. Your grant documents control many key details.
Could your equity award become a useful part of your financial future without creating a tax bill you cannot pay? That depends on more than the company’s latest valuation. I’ve seen employees focus on the number of options or units in an offer, then miss the exercise cost, settlement rules, or deadline that shapes their real choice.
The guide below explains how ISOs and RSUs work at private companies, what to check in your paperwork, and how to compare outcomes. It is general U.S. educational information, not tax or legal advice.
ISO and RSU Awards: Structure, Eligibility & Pre-IPO Context
An ISO is an employee stock option: a right to buy company shares at a set price, called the exercise price. An RSU is a promise to deliver shares or their cash value after stated conditions are met. Before an IPO, both awards may be hard to sell, and their stated value is not guaranteed cash.
How ISOs work before an IPO
An ISO gives you the choice, not the duty, to buy shares at the exercise price. You usually pay that price to exercise. The company sets it at no less than the stock’s fair market value on the grant date; for a 10% shareholder, the minimum is generally 110% of fair market value.
ISOs generally may be granted only to employees. Their statutory term is usually no more than 10 years, or five years for a 10% shareholder. Your grant agreement may set a shorter term or other conditions, so check the actual dates.
The $100,000 ISO limit is based on the grant-date fair market value of shares that first become exercisable as ISOs in a calendar year. Any excess generally receives nonstatutory option treatment. This is not a $100,000 limit on an award’s current value.
How RSUs work before an IPO
An RSU is not a share you own when it is granted. It is a promise to deliver shares, or sometimes cash, after conditions in the plan are met. You do not pay an exercise price, but you also do not choose when to buy shares.
RSUs often vest over time. At a private company, vesting may not mean the shares are delivered right away. Some plans defer settlement until a liquidity event, such as an IPO or sale. Others use additional conditions, often called double-trigger vesting: time-based vesting plus a qualifying event.
| Feature | ISO | RSU |
|---|---|---|
| What you receive | Right to buy shares | Promise of shares or, in some plans, cash |
| Cost to receive shares | Exercise price, plus possible tax | Usually no exercise price |
| Typical tax point | Exercise can affect AMT; sale may create tax | Usually when shares are delivered or settled |
| Private-company concern | Cash and possible AMT before a sale | Tax may arise before you can sell |
| Main documents to check | Option agreement and equity plan | RSU agreement and equity plan |
Share counts alone are not a fair comparison. An option’s value depends partly on its exercise price; an RSU’s value depends on the share value at settlement. Both may be affected by vesting, dilution, taxes, and whether a sale ever occurs.
Tax Treatment, Vesting & Key Plan Requirements
Tax timing is one of the biggest differences between these awards. ISOs may avoid regular federal income tax at exercise, but their spread can count for Alternative Minimum Tax. RSUs are generally taxed as wage income when shares are delivered or otherwise settled, with withholding. Plan terms determine when that happens.
ISO taxes: exercise, AMT, and sale
The spread is the difference between the fair market value at exercise and the exercise price. Exercising an ISO generally does not create regular federal income at that moment, but the spread may count in the AMT calculation. That can mean tax is due even when the shares cannot be sold.
A sale is a qualifying disposition only if you hold the shares for at least two years from the grant date and one year from the exercise date. If you sell sooner, some gain may be treated as ordinary compensation income. The exact tax result depends on the sale price, exercise price, and timing.
Leaving the company can start a short exercise clock. A plan commonly requires you to exercise within three months after employment ends to preserve ISO treatment. Different statutory periods apply for disability and death, and the agreement may impose its own expiration deadline. Confirm both the plan’s terms and the applicable tax rules before acting.
RSU taxes: vesting, settlement, and withholding
RSUs are generally taxed as ordinary wage income when shares are delivered or otherwise settled. The amount included in income is generally based on the shares’ value at that time. Employers usually withhold taxes, but withholding is not a guarantee that it covers your final tax bill.
At a private company, a key question is whether vesting and settlement happen together. If settlement is delayed until an IPO or another event, ask what event triggers delivery and tax. Also check whether the company can withhold shares, require cash for withholding, or use another method.
Decision Framework: Modeling Value, Liquidity & Risk
A useful comparison estimates what you might keep, when you need cash, and what happens if shares cannot be sold. Model several outcomes rather than relying on one company valuation. Include exercise cost, taxes, vesting, dilution, and the possibility that the shares become worthless or remain illiquid.
A practical comparison using scenarios
Consider an illustrative ISO grant of 10,000 options with a $2 exercise price. Exercising all options costs $20,000 before any tax. If the shares are valued at $5 at exercise, the spread is $30,000, which may affect AMT. That does not mean the employee can sell shares for $5.
Now consider 10,000 RSUs that settle when shares are valued at $5. Their gross value at settlement would be $50,000, and the value is generally treated as wage income. If no market exists, the employee may owe tax without being able to sell shares to raise cash. These simplified figures exclude vesting, tax rates, dilution, and other plan terms.
| Scenario | ISO question | RSU question |
|---|---|---|
| Company value rises | Can you fund exercise and possible AMT? | What tax applies at settlement, and can you sell? |
| Company value falls | Is exercise price now above share value? | What is the value when shares settle? |
| No IPO or sale | Can you afford to hold or lose the exercise cost? | Can settlement or tax occur without a market? |
| You leave | What is the post-termination exercise deadline? | What vested awards are retained, forfeited, or settled? |
Do not compare an option grant and an RSU grant by share count or the company’s headline valuation alone. Ask about the company’s fully diluted share count if available, the award’s place in the cap table, and how future financing could dilute ownership. A private valuation is not a promise of a sale price.
Gather facts and verify deadlines
Before modeling, collect the award agreement, equity plan, vesting schedule, and current fair market value or 409A valuation. Ask for company rules on option exercises, RSU settlement, liquidity, and what happens when you leave. A 409A valuation is a private-company tax valuation used in setting common-stock value; it is not a guaranteed price you can receive.
Then verify dates and triggers in writing. For ISOs, record the expiration date and post-termination exercise window. For RSUs, confirm whether vesting triggers tax or settlement, whether a liquidity event is required, and what happens to unvested and vested units if your job ends.
Liquidity Events, Employment Changes & Tax-Professional Review
Liquidity means being able to turn shares into cash through a permitted sale. An IPO may create a market, but it does not always allow immediate sales. A sale of the company, tender offer, or other event may have different rules. Before acting, match award terms and tax dates to realistic access to cash.
Illustrative pre-IPO situations
These examples are hypothetical, not actual employee case studies. They show why the same award can lead to different choices based on cash, deadlines, and settlement terms.
- ISO holder leaves before an IPO: The employee has three months under the plan to exercise and preserve ISO treatment. They compare the exercise cost and possible AMT with savings they can afford to risk. If they exercise, the shares may still be unsellable and could lose value.
- RSU holder reaches a vesting date: The units vest, but the agreement delays settlement until a qualifying event. The employee confirms whether this is a double-trigger arrangement and asks what happens if they leave before settlement. The answer depends on the plan, not the label “RSU.”
- Employee receives both awards: The employee models each grant separately, including taxes and cash needs. They avoid treating the company’s preferred valuation as cash and ask a tax professional to review the timing before exercising or making an election.
Use a four-step review before you decide
- Gather the documents. Get the plan, award agreements, vesting schedule, valuation, and written liquidity rules.
- Model more than one outcome. Estimate after-tax results at several share values, including no liquidity or a total loss. Include exercise costs, AMT, wage income, withholding, and dilution.
- Check every deadline. Confirm the ISO expiration and post-employment window. For RSUs, identify the exact vesting, settlement, and tax triggers.
- Get qualified advice. A tax professional familiar with private-company equity can review tax estimates. An attorney may help interpret plan terms. Keep grant, exercise, payment, and share-delivery records.
The practical choice is not “Which award is better?” It is “Which award’s costs, tax timing, and risks fit my situation?” Do not exercise only to start a holding period without modeling the cash required, possible AMT, deadline, and risk that shares never become liquid.
FAQs About Pre-IPO ISOs and RSUs
These answers give general U.S. guidance, but your award documents and personal tax situation matter. Use the questions to identify what to verify with your employer and advisers before you exercise, sell, or make a tax decision.
Are ISOs better than RSUs before an IPO?
Not in every case. ISOs may offer favorable tax treatment if rules are met, but exercise can cost cash and trigger AMT. RSUs avoid an exercise price but can create wage tax at settlement.
Do I pay tax when I exercise an ISO?
Usually, ISO exercise does not create regular federal income tax at exercise. However, the spread may count for AMT. State tax rules and personal circumstances can also affect the result.
When are RSUs taxed at a private company?
Generally, RSUs are taxed as wage income when shares are delivered or otherwise settled. Some plans defer settlement until a liquidity event, so check the agreement for its tax and delivery triggers.
What is the ISO $100,000 rule?
It generally limits the grant-date fair market value of shares first exercisable as ISOs in one calendar year to $100,000. Any excess shares are generally treated as nonstatutory options.
How long do I have to exercise ISOs after leaving?
A plan commonly allows three months to exercise and preserve ISO treatment. The agreement may set a shorter period, and different statutory periods apply in cases such as disability or death.
What does a qualifying ISO sale mean?
Generally, it means selling shares at least two years after the grant date and one year after exercise. A sale before both holding periods end may cause some gain to be treated as compensation.
Can RSUs create tax before I can sell the shares?
Yes. If shares are delivered or settled while the company is private, tax may apply even if there is no public market. Ask how the company handles withholding and liquidity.
What should I compare besides the number of shares?
Compare the ISO exercise price and cost, tax timing, vesting, settlement rules, deadlines, dilution, and ability to sell. Also model a low-value outcome or no liquidity.
Should I exercise ISOs just to start the holding period?
Not without reviewing the full cost and risk. Consider exercise cash, possible AMT, the option deadline, and the chance you cannot sell the shares or may lose their value.
Does an IPO mean I can sell immediately?
No. Lockups, trading rules, and company policies may limit sales after an IPO. Confirm when you can sell and whether any other restrictions apply.
(This article was written by one of our staff writers, James Holloway. Visit our Meet the Team page.)
