Roughly 8 million unmarried couples live together in the United States according to Census Bureau data from 2023, and most of them have no legal document spelling out what happens to the house, the joint bank account, or the dog if the relationship ends. A cohabitation agreement is the private contract that fills that gap, and it matters more the longer two people share finances without a marriage license.
What a Cohabitation Agreement Actually Covers
A cohabitation agreement is a contract between two unmarried partners that spells out how property, debt, and expenses get handled during the relationship and how they get divided if it ends. It typically addresses who owns what going into the relationship, how a jointly titled home or car gets split on separation, whether one partner owes the other anything resembling support, and who’s responsible for shared debt like a car loan or credit card opened jointly. Some couples also use it to set expectations around pet custody, since unlike children, pets are treated as property in every US state and a judge won’t apply a “best interests” standard to a dispute over a golden retriever.
The agreement does not need to be filed with any court or government office to be valid. It just needs to be signed, ideally notarized, and — this is the part people skip — supported by some exchange of value (lawyers call this “consideration”) so a court doesn’t later toss it out as an unenforceable gift promise.
Busting the Common Law Marriage Myth
The single biggest misconception is that living together for some number of years automatically creates a “common law marriage” with spousal rights. That’s false in the overwhelming majority of the country. Only a handful of states — Colorado, Iowa, Kansas, Montana, New Hampshire (for inheritance purposes only), South Carolina (phased out for relationships starting after 2019), Texas, and Utah, plus the District of Columbia — recognize common law marriage at all, and even there it requires proof of intent to be married, not just cohabitation. In California, Illinois, New York, and roughly 40 other states, two people can live together for 20 years and share three kids without acquiring a single automatic marital right. No community property division, no spousal support obligation, no automatic inheritance if one partner dies without a will.
That gap is exactly why the 1976 California Supreme Court case Marvin v. Marvin still gets cited in family law circles. Actor Lee Marvin’s former partner Michelle Triola sued for a share of his earnings after their six-year relationship ended, and the court ruled that unmarried couples can enforce express or implied contracts about property and support — but only if such an agreement can be shown to exist. That ruling is the legal foundation “palimony” claims rest on nationwide, and it’s also the reason attorneys tell cohabiting clients: don’t rely on an implied agreement a court might infer years later from your conduct. Write it down.
Building the Agreement Step by Step
A workable cohabitation agreement usually gets built in this order:
1. List separate property each partner owned before moving in together — bank account balances, the car, any retirement accounts — with approximate values and dates.
2. Decide how new joint property gets titled and divided, especially real estate. If one partner pays a $60,000 down payment on a $400,000 house titled in both names, the agreement should state whether that partner gets the $60,000 back off the top before an even split, or whether it’s treated as a gift to the relationship.
3. Address household expenses — an even 50/50 split rarely matches an income gap of, say, $95,000 versus $45,000, so many agreements set a proportional contribution instead.
4. Decide what happens to shared debt on separation, particularly co-signed auto loans or credit cards.
5. Add a dispute resolution clause — mediation before litigation saves both people from a contested court battle that can run $10,000–$25,000 in attorney fees per side even in a modest dispute.
Each partner should ideally have their own attorney review the document before signing. Using one lawyer for both sides is a common shortcut that later gets an agreement challenged for lack of independent counsel, especially if there’s a significant income or asset gap between the partners.
How This Differs From a Prenuptial Agreement
A prenup only takes effect if the couple marries; a cohabitation agreement stands on its own regardless of marriage plans, and it’s enforceable purely as contract law rather than family law. That distinction matters procedurally — a cohabitation dispute usually gets litigated in civil court under breach-of-contract rules, not in family court under equitable distribution statutes, which changes both the procedure and, in some states, the statute of limitations that applies. Couples who later do marry sometimes convert their prenuptial agreement terms directly from their existing cohabitation agreement, since the financial disclosures are often already done.
Common Mistakes Partners Make
The most frequent error is drafting the agreement only after a breakup is already brewing — by that point one partner is usually unwilling to sign anything, and courts view an agreement signed under obvious duress skeptically. Another common mistake is failing to update the document after a major life event, like paying off a mortgage together or having a child; an agreement drafted in year one that never gets revisited often no longer reflects reality by year eight. A third mistake is leaving out estate planning entirely — cohabitation agreements don’t grant inheritance rights, so a partner who dies without a will can leave their surviving partner with nothing, since unmarried partners aren’t included in state intestacy statutes. Pairing the agreement with a will and, in states that recognize it, a durable power of attorney for healthcare decisions closes that gap — without one, a hospital may only recognize blood relatives for medical decision-making, regardless of how long the couple has lived together.
Frequently Asked Questions
Does a cohabitation agreement need to be notarized to be valid?
Notarization isn’t legally required in most states for the contract itself to be enforceable, but it strengthens the document’s credibility if it’s ever challenged in court and is standard practice for any agreement covering real property.
Can a cohabitation agreement include child custody terms?
No. Custody and child support are always decided under each state’s family law standards and can’t be pre-set by private contract the way property division can — a family court will review those terms independently regardless of what the agreement says.
What happens if we never sign one and then separate?
Without an agreement, property typically gets divided based on legal title alone rather than contribution or fairness, meaning the partner whose name is on the deed or account usually keeps it, regardless of what the other partner paid toward it.
Putting a cohabitation agreement in place while the relationship is stable, rather than after cracks appear, is what makes the document hold up — both legally and practically — if circumstances change.