RSU vs ISO vs NSO: What Each Means for Your Prenup

Why Equity Compensation Belongs in Your Prenup Conversation

RSUs, ISOs, and NSOs are each treated differently in a prenup, and a prenup lets couples decide together how each type is classified rather than leaving it to state defaults. This is a conversation about planning with your partner, not one about defending against them.

For many professionals, equity compensation represents the largest single component of their net worth. A senior software engineer at a publicly traded company might receive $150,000 to $400,000 in RSUs over a four-year vesting period, while a startup founder could hold options worth multiples of their salary if the company goes public. When that equity is tied to vesting schedules, tax treatment, and future appreciation, the financial picture becomes genuinely complex.

Without a prenup, your state's default property rules control how that equity is divided if the partnership ends. In community property states, equity earned during the marriage is typically split roughly 50/50. In equitable distribution states (the majority), courts divide it based on what they consider fair, but the employee spouse rarely keeps all of it. Either way, the decision is made for you.

A prenup replaces those defaults with a rule you and your partner choose together. It can address classification, valuation, vesting timelines, tax burdens, and even future grants that haven't been issued yet. Because these pieces interact (the tax treatment of an ISO is different from an RSU, which changes who benefits from holding versus selling), the process works best when attorneys, CFPs, and CPAs collaborate. That's exactly how Neptune's lawyer-led online prenup process works, coordinating all three professionals to shepherd the agreement from first conversation to final signature.

What Is the Difference Between RSUs, ISOs, and NSOs?

RSUs are promises of actual company shares delivered once vesting conditions are met, with no purchase required. ISOs (incentive stock options) give you the right to buy shares at a predetermined strike price with potentially favorable tax treatment. NSOs (non-qualified stock options) also let you buy shares at a strike price, but the spread is taxed as ordinary income at exercise.

Here's how they compare across the dimensions that matter most for a prenup:

The differences in tax character and timing directly shape how each type should be addressed in a prenup. For example, an ISO holder who meets holding period requirements pays long-term capital gains rates (0%, 15%, or 20% in 2025), while an RSU recipient pays ordinary income rates (up to 37% federal in 2025) the moment shares land. Those different tax bills change the real after-tax value each partner walks away with, which is why the prenup should specify who bears the tax liability, not just who gets the shares.

How Are RSUs and Stock Options Classified as Separate or Shared Property?

Equity granted during the marriage is generally treated as shared property (marital or community) even when unvested, and the grant date relative to the wedding is the single most important classification factor.

State law controls how property is classified. In community property states (California, Texas, Arizona, Idaho, Louisiana, Nevada, New Mexico, Washington, and Wisconsin under similar rules), assets earned during the marriage belong equally to both spouses by default. In equitable distribution states (New York, Florida, Illinois, and most others), courts divide marital assets based on fairness, considering factors like each spouse's financial contributions and the length of the marriage. But in both systems, stock options and equity granted during the marriage are presumed to be shared property.

Illinois makes this particularly explicit. Under 750 ILCS 5/503(b)(3), stock options and restricted stock granted during a marriage are presumed marital property "whether vested or non-vested or whether their value is ascertainable." The fact that the shares haven't been delivered or that the current value is unclear doesn't remove them from the shared estate.

Beyond the grant date, courts also look at what the equity was designed to reward:

• Past services: A grant meant to compensate work already performed before the marriage leans toward separate property.
• Present services: A grant tied to ongoing employment during the marriage is typically shared.
• Future services: A grant intended to retain the employee for future work may be partially shared and partially separate, depending on how much of the retention period falls within the marriage.

This three-way classification is why a prenup needs specificity. A couple can agree that pre-marriage grants remain separate, that during-marriage grants are shared, and that future grants follow a formula they pick together. That level of clarity is exactly what the default rules don't provide.

How Do Coverture and California's Hug and Nelson Formulas Divide Unvested Equity?

Courts commonly use a coverture fraction (the number of months worked during the marriage while the grant was vesting, divided by the total number of months in the vesting period) to calculate the shared portion of unvested stock options and RSUs.

Here's a simple example. Say you receive a four-year RSU grant two years before your wedding. You marry, and the remaining two years of vesting occur during the marriage. Under a coverture fraction, 2 out of 4 years (50%) of the grant would be classified as shared property. If the grant was for 1,000 shares at $100 each, roughly $50,000 worth of shares would fall into the shared pool absent a prenup.

California, home to a large share of tech equity holders, has the most developed case law on dividing unvested equity. Two formulas dominate:

• The Hug formula (Marriage of Hug, 1984) applies when a grant was primarily meant to induce employment or reward past service. The denominator runs from the grant date to the vesting date. Because the entire period from grant to vest is in play, a longer pre-marriage employment period reduces the community share.
• The Nelson formula (Marriage of Nelson, 1986) applies when a grant was primarily intended to incentivize future performance. The denominator runs from the start of employment to the vesting date, which typically increases the community share because more of the total period falls within the marriage.

Courts retain broad discretion to choose which formula fits the facts, and neither is mandatory. That uncertainty is precisely why couples benefit from addressing unvested equity in a prenup. You can replace both formulas with your own agreed-upon rule, whether that's a fixed percentage, a modified coverture fraction, or a provision that all unvested grants remain with the employee spouse while the other spouse receives equivalent value from a different asset.

For a deeper walkthrough of how equity vesting interacts with prenup clauses, Neptune's tech equity guide covers cliff schedules, performance triggers, and more.

How RSU, ISO, and NSO Taxes Change What a Prenup Should Address

RSUs are taxed as ordinary income at vesting, NSOs are taxed as ordinary income at exercise on the spread, and ISOs can qualify for long-term capital gains if specific holding periods are met, though they may trigger the Alternative Minimum Tax (AMT) at exercise.

These tax differences have real dollar consequences for prenup planning:

• RSUs: When shares vest, the fair market value is taxed as ordinary income. For a high earner in California, the combined federal (37%) and state (up to 13.3%) marginal rate can exceed 50% in 2025. Employers typically withhold shares to cover taxes, but the withholding rate (often 22% federal supplemental) frequently under-covers the actual liability, leaving a bill at tax time.
• ISOs: If you hold the shares for at least two years from the grant date and one year from the exercise date, the gain qualifies for long-term capital gains rates (0%, 15%, or 20% in 2025). But the spread at exercise (market price minus strike price) is a preference item for AMT, which can create a significant tax bill in the exercise year even when you haven't sold anything. ISOs are also subject to a $100,000 annual vesting limit; amounts exceeding that threshold are automatically treated as NSOs.
• NSOs: The spread at exercise is taxed as ordinary income and is also subject to FICA taxes (Social Security up to $176,100 in 2025, plus 1.45% Medicare with no cap and an additional 0.9% for earnings above $200,000). There's no favorable capital gains treatment on the spread.

Under 26 U.S.C. Section 1041, transfers of property between spouses incident to divorce are tax-free. But the tax doesn't disappear. It shifts. The receiving spouse inherits the transferring spouse's cost basis and pays full income tax when the shares vest or the options are exercised. If your prenup assigns RSUs to one partner but doesn't specify who covers the tax bill, the partner receiving the shares could face a tax liability equal to 40% or more of their value.

A well-drafted equity clause should specify:

1. Whether tax-gross-up payments (one spouse covering the other's tax liability) apply.
2. How liquidity is handled if shares can't be sold immediately (common with pre-IPO equity or lockup periods).
3. Whether the AMT credit from ISO exercises is factored into the division.

Because tax planning interacts with legal classification and financial projections, this is where having attorneys, CPAs, and CFPs working together matters most.

How Couples Draft Enforceable Equity Clauses With the Right Professionals

Enforceable equity clauses identify specific grants by name and date, describe vesting schedules, confirm that both partners made full financial disclosure, and set a chosen rule for appreciation and future grants. Generic language almost always falls short.

A California court, for instance, will look closely at whether a prenup clause actually addressed vesting structures, reimbursement rights, and separate versus community characterization. Writing "all stock options remain separate property" without identifying the grants, disclosing the values, or addressing during-marriage appreciation leaves the clause vulnerable to challenge. And if the employee spouse deposits vested share proceeds into a joint checking account, that co-mingling can undermine a separate-property claim regardless of what the prenup says.

Here's what a strong equity clause typically includes:

• Grant-specific identification: Company name, grant date, number of shares or options, strike price (for options), and vesting schedule.
• Classification rule: Whether the grant is separate property, shared property, or subject to a custom formula (like a modified coverture fraction).
• Appreciation treatment: Whether growth in value during the marriage is separate or shared.
• Future grants: A default rule for equity awarded after the wedding (for example, all future RSUs are shared, or future grants follow the same coverture formula).
• Tax allocation: Which spouse bears the income tax at vesting or exercise.
• Anti-co-mingling protocol: Instructions for maintaining separate brokerage accounts for pre-marriage equity.
• Full disclosure attachment: A schedule listing every current grant with its fair market value as of a stated date.

As Michael C. Cotugno, Esq., Managing Partner of Neptune Legal, puts it: "Fairness in a conscious partnership transcends mere numbers." The goal isn't to win a negotiation. It's to build a framework both partners trust.

Independent counsel for each partner is highly recommended for an enforceable prenup. Courts in most states scrutinize whether both parties had the opportunity to consult their own attorney before signing.

Cost context: DIY prenup templates typically run $0 to $700, but they rarely handle equity compensation with the specificity courts require. Attorney-drafted prenups addressing equity generally cost $4,000 to $10,000 or more, depending on complexity. Neptune's lawyer-led online prenup process pairs each couple with attorneys who have 20+ years of experience, along with CFPs and CPAs who coordinate on tax modeling and financial projections, all managed end to end so nothing falls through the cracks.