Separate Property, Community Property, and Commingling

Nine states^$†$ — California, Texas, Washington, and six others — are community property states; the rest follow common-law (equitable-distribution) rules. Which set governs you is determined by domicile, and it changes when you move. A couple that builds a portfolio in a common-law state and retires to California has just walked their assets into a different rulebook.

The baseline rule is simple, and California states it in two sentences of statute: everything acquired during the marriage while domiciled in the state is community property ( Cal. Fam. Code §760), while property owned before the marriage, plus anything either spouse receives during the marriage by gift, bequest, or inheritance, and the rents and profits of all of it, is separate property ( §770). Everything earned by either spouse’s labor during the marriage is community. The simplicity ends at commingling. The §760 presumption is the default, and the moment separate property is mixed with community property so that the two can no longer be traced, the entire pool stays community by operation of that presumption. Deposit a $200,000 inheritance into the joint checking account that the household paychecks flow through, use it for a few mortgage payments, and you have very likely converted half of it into your spouse’s property — not through malice, but through a deposit slip.

The discipline that prevents this is unromantic but cheap:

• Keep pre-marital assets and inheritances in accounts titled in your name alone, and never route a community-money paycheck through them.
• Do not use community funds to improve separate property or pay down its debt. Under the Moore/Marsden rule ( In re Marriage of Moore, 28 Cal. 3d 366 (1980); In re Marriage of Marsden, 130 Cal. App. 3d 426 (1982)), community payments against the principal of a separate-property house buy the community a pro rata ownership interest plus the same pro rata slice of the appreciation during the marriage — the ratio being community principal paid over the original purchase price. If the community retires $200,000 of principal on a house bought for $1 million shortly before the wedding and now worth $3 million, the community’s claim is $\$200,000+(\$200,000∕\$1,000,000)\times \$2,000,000=\$600,000$, not the $200,000 you actually paid. Appreciation that occurred before the marriage stays separate.
• Run the trade in the other direction and you get far less. Separate property contributed to the acquisition of a community asset earns only a dollar-for-dollar reimbursement, with no interest and no share of appreciation ( Cal. Fam. Code §2640), and only if you can trace it. A $500,000 separate down payment on a house that doubles returns $500,000.
• Document the trail. The burden of proof falls on whoever later claims an asset is separate; account statements are that proof.

Transmutation: Changing the Character on Purpose The character of property is not fixed — spouses can convert separate property into community property, or the reverse, by transmutation. Do it deliberately and in writing, because California requires an express written declaration made, joined in, consented to, or accepted by the spouse whose interest is adversely affected ( Cal. Fam. Code §852). A deed, an account title, or a course of conduct is not enough; the writing must say on its face that the character of the property is being changed. Oral agreements and helpful assumptions fail.

Transmutation cuts both ways, which is exactly why it deserves a deliberate decision, not passive drift. Converting separate property into community property surrenders half of it in a divorce — and buys a full basis step-up on the whole asset at the first death instead of half of one, which on a long-held appreciated portfolio is worth six or seven figures (section “Capital Gains Resets With Inheritance”). Converting community property into separate property does the opposite. Which trade is right depends on how you rate the probability of divorce against the certainty of death; what is never right is leaving the question to a deposit slip. Couples in common-law states can reach the same step-up result without moving, using an opt-in community property trust (section “Capital Gains Resets With Inheritance”).

When You Move Crossing a state line does not re-characterize what you already own, but it changes the rules going forward and can change how the new state divides the old assets. California solves this with quasi-community property: property acquired elsewhere that would have been community property had you been domiciled in California when you acquired it is treated as community property on divorce or death ( Cal. Fam. Code §125). A couple who spent twenty years building a portfolio in New York on one spouse’s salary and then retires to California has just walked that portfolio into a fifty-fifty rulebook. The reverse move is worse in a different way: community property carried into a common-law state generally keeps its community character, but only if you can prove it, and only if you have not commingled it since. Retitle and document at the moment of the move instead of waiting for a dispute to flare up.

None of this is romantic. Neither is the alternative conversation, conducted under oath in a deposition. For the federal treatment of community property, see IRS Pub. 555, “Community Property”.