What Happens If You Don’t Get a Prenup in California?

If you get married in California without a premarital agreement, the law already has one for you.

Under California’s Family Code, there are default rules that govern how your income, assets, debts, and even spousal support are handled if your marriage ends in divorce—or if you pass away without an estate plan. These are often referred to as California’s default prenup.

For some couples, the default rules are just fine. For others, learning the default helps clarify what they’d like to change through a formal premarital agreement. Either way, understanding what the law says by default is an essential first step.

Community Property: You’re in It Together

When you get married, you become part of what the law calls “the community.” That means:

• Earnings during marriage are shared equally—even if the income is deposited in an account under one person’s name.

• Assets acquired during marriage are presumed to be community property.

• Employment benefits, like stock options, retirement contributions, and bonuses, are community property if earned during marriage, even if they vest later.

Separate Property: What’s Yours Stays Yours (Mostly)

Some things remain separate property by default, such as:

• Property owned before marriage

• Gifts or inheritances received during the marriage

• Income earned after separation

But it’s not automatic. If there’s a dispute, you’ll need clear records showing where the asset came from and how it was kept separate. Also, if your efforts during the marriage increase the value of separate property (like managing a business), some of that growth could become community property.

Homes, Businesses, and Mixed Assets

• Using separate property (like an inheritance) to buy a home in joint names? You may only be entitled to reimbursement of your contribution—not a share of the home’s appreciation.

• A business you owned before marriage stays separate, but if it increases in value during the marriage, the community may gain an interest.

• If you inherit a home and keep it in your name, it remains separate—but using community funds to pay the mortgage may give the community a share of the appreciation.

Debts: Not Always Personal

• Debts from before marriage remain your responsibility—unless community funds are used to pay them.

• Debts during marriage are generally shared, even if one spouse doesn’t agree with how the money was spent—unless the debt was clearly unrelated to the marriage.

Divorce: Splitting Property and Debts

By default:

• Community assets and debts are divided equally, though the court can divide them through sales or offsets (e.g., one person gets the house, the other gets an investment account of equal value).

• A spouse who remains in the home after separation may owe “rent” to the community.

• Spouses who pay community debts after separation are generally reimbursed—unless the payments replace support.

Spousal Support: Not Automatic, But Possible

Each spouse has a duty to support the other. If one person earns significantly more, spousal support may be ordered. While premarital agreements can limit or waive support, a court can still order support if it finds that enforcing the waiver would be unconscionable—a legal standard meaning “grossly unfair.”

Estate Planning: The Law Has a Plan (Whether You Like It or Not)

If you pass away without a will or trust:

• Your share of community property goes to your spouse.

• Your separate property is divided between your spouse and other family members, depending on who survives you.

A premarital agreement can change those default inheritance rules too—either to give more or less to a surviving spouse.

So, Should You Get a Premarital Agreement?

Maybe. Maybe not.

Whether a premarital agreement makes sense depends on many things—one of which is how well California’s default rules align with your goals. Some couples choose to stick with the default but put it in writing to clarify expectations and reduce future conflict. Others want to make specific changes.

At a minimum, I recommend having the conversation. Understanding the default rules is the best place to start.

What Is the Date of Separation and Why Does It Matter in a California Divorce?

In California divorce cases, few things carry as much legal and financial weight as the date of separation. It marks the dividing line between what’s considered community property—shared by both spouses—and what’s separate property, belonging to just one person. And yet, this one date is often a point of serious disagreement.

What is the Legal Definition?

Under California law, the date of separation is the day when:

1. One spouse clearly communicates to the other that the marriage is over; and

2. Their behavior after that point is consistent with the decision to end the marriage.

It’s not enough to just say you’re done. The court looks for actions that show you meant it—moving out, setting up a separate bank account, telling friends and family, or changing how you live together (or don’t).

Why It Matters

Property Division

California is a community property state. That means anything earned or acquired between the date of marriage and the date of separation is generally split 50/50. But anything acquired after the date of separation is usually separate property. So if your spouse got a bonus or bought a house after the separation date, that could be yours—or theirs—depending on what the court finds.

Spousal Support

The length of your marriage affects spousal support. If the date of separation makes the marriage under 10 years, the court may limit support to half the length of the marriage. If it’s over 10 years, it could be considered a long-term marriage, with different support rules.

Debt Responsibility

Just like assets, debts incurred during the marriage are presumed community. After separation, those debts are typically the responsibility of the person who incurred them.

It’s Not Always Clear

Sometimes, the date is obvious—someone moves out and says, “It’s over.” Other times, things are murky. Maybe one spouse files for divorce but then reconciles. Maybe you stayed living under the same roof but stopped being a couple in every other way. In cases like these, courts will dig into the details: emails, texts, lease agreements, bank records, even holiday photos.

If You Disagree on the Date

Disputes over the date of separation are common and can lead to a trial. Both sides will present evidence to support their version of events. The judge will decide which story lines up with the law and the facts.

Bottom Line

If you’re separating or divorcing, be thoughtful about when and how you communicate your intent to end the marriage—and how your actions line up afterward. The date of separation isn’t just symbolic; it can significantly affect your financial future.

If you’re unsure how the date of separation might affect your case, or you’re in a dispute about when the separation occurred, I can help you sort through the facts and prepare a strong case.

Transmutation Agreements in California: best practices

In California, spouses can change the character of property — from separate to community, or vice versa — through a written agreement known as a transmutation. The relevant statutes make this seem straightforward. Family Code section 850 permits transmutation by agreement or transfer, and section 852 sets out the formal requirements: the change must be made in writing, contain an express declaration, and be accepted or consented to by the spouse whose interest is adversely affected.

In practice, enforceability often turns on a much deeper question:

Did the disadvantaged spouse know exactly what they were giving up, and why?

This question becomes especially important when the transaction results in one party walking away with more money, more property, or a better long-term financial position than the other. The moment one spouse receives a material benefit from the transaction — such as sole title to a home — Family Code section 721 triggers the presumption of undue influence.

At that point, it’s not enough to produce a signed deed or agreement. The advantaged spouse must affirmatively prove that the disadvantaged spouse acted with full knowledge, voluntary intent, and a complete understanding of the legal effect of the change. Without that showing, the transaction may be set aside, even if it otherwise complies with section 852.

What the Case Law Emphasizes

The foundational cases (e.g., Estate of MacDonald, Valli, Benson, Brace) have made clear that:

• A valid transmutation must contain express language showing a clear intent to change ownership or character of the property.

• You can have a valid transmutation but still fail the test of whether there was undue influence.

• Evidence Code section 662 (presumption based on title) does not override the presumption of undue influence under Family Code section 721 in marital transactions.

• When the facts suggest an imbalance — such as a quitclaim deed signed without consideration — the burden shifts to the advantaged spouse to prove that the other party knowingly and voluntarily agreed.

Courts have consistently applied the undue influence presumption in cases where property was transferred without reciprocal benefit. In these cases, the failure to show informed consent, even with a signed deed, was fatal to enforcement.

Drafting and Procedural Safeguards

To protect a transmutation from challenge, it is not enough to meet the statutory elements. Counsel should ensure that the record demonstrates the disadvantaged spouse:

• Had full and accurate disclosure of the property’s nature and value

• Understood the legal and financial consequences of the change

• Was not under pressure to sign (timing around real estate closings is particularly risky)

• Had time to consult with independent legal counsel

For higher-risk transactions, such as interspousal transfers of real property without consideration, it may be wise to include explanatory language directly in the instrument, separate acknowledgments of understanding, and, ideally, documented advice or waiver of separate counsel.

The Practical Takeaway

Transmutations are not mere formalities. When challenged, they are scrutinized for intent, clarity, and fairness — particularly where one spouse gives up a valuable interest and receives little or nothing in return.

To withstand that scrutiny, we must ask the same question the court will ask later:

Did the disadvantaged spouse know what they were giving up, and why?

If the answer is anything less than a well-documented yes, the agreement may not survive.

Why Prenups Have Clear Rules About Debt and Separate Property in Marriage

Under default California law, anything earned during marriage is presumed to be community property. Debts incurred during marriage are also presumed to be shared. It’s easy to assume that if something is in your name, it stays yours. But once loans, shared income, or separate property come into play, things get complicated quickly.

In prenups and postnups, lawyers who specialize in this area include specific language about the use of credit, collateral, and separate property. Without that clarity, we find that couples can be confused about the rules and sometimes in court.

Here’s what that looks like in real life:

Using a loan to improve your own separate property doesn’t mean your spouse now owns part of it.

If someone takes out a loan during marriage in their own name to renovate a home they owed before marriage and uses earnings from work to pay it off, that doesn’t automatically make all of the home community property. Judges often look at what the lender expected when issuing the loan and what income stream was intended to pay it back. If community earnings were used, the loan may not be treated as separate.

Paying for repairs or taxes with joint money doesn’t make the property joint.

Community funds sometimes cover property taxes or maintenance on a separately owned home. That doesn’t turn the home into community property. But if things fall apart, people often feel entitled to equity based on how money was used. A prenup can clarify. 

Being an authorized user on a spouse’s credit card can create confusion about debt.

If one spouse opens a credit card in their name and adds the other as an authorized user, they may assume they are the only one responsible. But if the card is used for joint expenses, California law might treat the debt as community. A prenup can clarify that the cardholder takes responsibility or, alternatively, that the debt is shared. Either way, it’s better to be explicit.

These examples reflect real choices people make in marriage. Helping each other, blending finances, making things easier. But without clear agreements in place, those decisions can lead to misunderstandings and resentment.

These clauses do more than protect people legally. They reduce conflict. They make it easier to trust that decisions made in good faith won’t be misunderstood later. A good prenup just puts into writing what people already believe to be fair. 

Prenups for Startup Founders: How to Share Some, Not All, of the Business

If you own a startup before marriage, you may want to protect your ownership while still recognizing your spouse’s potential contributions to your future success. California law lets you decide what remains separate and what becomes community property. A well-drafted prenuptial agreement can define a middle ground that avoids default rules and future conflict.

Here’s how to structure an agreement when you want to keep most of your business separate but allow some of it to be shared.

Start with a Baseline

Identify what you own before marriage. This includes equity, IP, trademarks, customer lists, and any unvested options. This forms your separate property foundation.

Decide What to Share

You don’t have to choose all or nothing. You can make specific parts of the business or future value community property. Here are a few ways to do that:

Share appreciation above a threshold

You can agree that the first $1 million of appreciation remains separate. Anything above that becomes community property and gets split equally if you divorce. This protects early risk while sharing long-term upside.

Share liquidity, not ownership

You can keep 100 percent of the business as separate property but agree to share some of the cash if the company is sold or you receive distributions during the marriage. For example, you might agree that 25 percent of any net payout during the marriage becomes community property.

Provide a fixed community reimbursement

If your spouse will support the household while you work long hours, you can include a flat payment in case of divorce. For example, after five years of marriage, your spouse receives $250,000 as recognition for that support. This avoids valuation battles and honors their contribution.

Use a split-growth formula

You can apply a simple formula to divide appreciation. For example, you get a 6 percent annual return on your premarital business value. Any growth beyond that is community property. This mirrors how courts might divide a business but does it upfront, avoiding a fight.

Make future compensation community

If you’re receiving new stock grants or options after marriage, you can agree those are community property, while keeping the original business separate. This works well when equity is tied to continued service.

Plan for clarity and track it

Whatever you agree to, spell it out in plain language and keep good records. Use regular valuations, document distributions, and track equity grants. That way, there’s no guesswork later.

Conclusion

You don’t need to hand over half your startup to be fair. A thoughtful prenup can protect your hard work while acknowledging your spouse’s role in your life and business. When done right, it keeps your intentions clear and your partnership strong.