By Harry Prabandham · Updated September 28, 2026
Personal Finance
Prenuptial and Postnuptial Agreements: A Financial Planning Guide
A prenup or postnup sets how assets, debts, and income are treated if a marriage ends. State law governs enforceability; each spouse needs counsel.
Prenuptial and Postnuptial Agreements: A Financial Planning Guide
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What does a prenuptial agreement do?
- It is a contract signed before marriage that defines which property stays separate and how assets would be divided at divorce or death.
- Without one, state law decides; California and other community property states split marital property, while most states use equitable distribution.
- A postnuptial agreement does similar work after the wedding, often after a liquidity event, inheritance, or new business.
- It is a legal document; Rubric coordinates the financial side, while each spouse's own attorney drafts and reviews it.
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Full Guide
What does a prenuptial agreement do?
- It is a contract signed before marriage that defines which property stays separate and how assets would be divided at divorce or death.
- Without one, state law decides; California and other community property states split marital property, while most states use equitable distribution.
- A postnuptial agreement does similar work after the wedding, often after a liquidity event, inheritance, or new business.
- It is a legal document; Rubric coordinates the financial side, while each spouse's own attorney drafts and reviews it.
What makes a prenup enforceable in California?
- The agreement must be in writing and signed by both parties under California's Uniform Premarital Agreement Act.
- At least seven calendar days must pass between first receiving the final agreement and signing it.
- An agreement unconscionable when signed can be set aside if the party also lacked fair disclosure of the other's finances and didn't waive it in writing.
- A spousal support provision is unenforceable if the affected party lacked independent counsel or if it is unconscionable when enforced.
How are stock options and RSUs treated?
- Equity granted before marriage but vesting during it can be partly community property, and California courts apportion it with time-based formulas.
- Grants made during the marriage are generally community property to the extent they reward work done during the marriage.
- An agreement can set how pre-marital grants, refresh grants, and post-exercise appreciation will be classified.
- Records of grant dates, vesting schedules, and exercises make any formula easier to apply later.
Can a prenup waive rights in a 401(k)?
- Federal law gives spouses survivor rights in many employer retirement plans, and only the spouse can waive them.
- Treasury regulations state that an agreement signed before marriage does not satisfy the spousal consent requirement.
- A valid waiver is generally a plan-specific consent signed after the wedding and witnessed by a notary or plan representative.
- IRAs are not covered by these federal rules, though state community property law can still give a spouse an interest.
What do these agreements typically cover?
- Classification of pre-marital assets, debts, businesses, and expected inheritances as separate property.
- Whether income, savings, and growth on separate property during the marriage stay separate or become shared.
- How commingled accounts will be traced when separate money lands in joint accounts.
- Property division and, within state limits, spousal support; a child's right to support cannot be reduced by agreement.
Do postnuptial agreements follow the same rules?
- Spouses in California owe each other fiduciary duties, which shape how courts review agreements made during marriage.
- When a postnup gives one spouse an advantage, courts can presume undue influence and require the favored spouse to rebut it.
- Changing property from separate to community, or the reverse, requires a writing with an express declaration by the affected spouse.
- Full disclosure and separate counsel for each spouse matter even more after the wedding.
Key takeaways
- A prenup or postnup replaces state default rules with terms both parties choose, within legal limits.
- California requires a writing, disclosure, and a seven-day review period, and closely reviews support waivers.
- Equity compensation needs specific drafting, and a prenup alone does not waive 401(k) survivor rights.
- Each spouse needs independent counsel; Rubric does not give legal advice.
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