Married couples get a body of law built around them by default. If a marriage ends, there are rules — state-specific, but rules — for how property gets divided and whether support is owed. Unmarried couples who live together generally get none of that. Whatever happens to your shared apartment, your joint savings, or years of combined financial life if you break up depends almost entirely on what you documented, agreed to, or can prove — not on how long you were together or how intertwined your lives became.
That surprises a lot of people. This article covers what actually happens without an agreement, what a cohabitation agreement can do about it, and a few concepts — like palimony and common law marriage — that come up constantly in this space and are widely misunderstood.
- What generally happens to your property and finances without an agreement
- What a cohabitation agreement actually is — and why it's contract law, not family law
- What it can generally cover
- Palimony and the case that created the concept
- The common law marriage wrinkle almost no one accounts for
- What a cohabitation agreement generally can't do
What generally happens without an agreement
In most states, unmarried partners are treated as legally separate individuals with no automatic rights to each other's property, income, or support if the relationship ends. Whoever holds title to an asset, or whoever purchased it, generally keeps it — regardless of how the couple actually used or contributed to it while together.
If only one partner's name is on the lease, the mortgage, or the car title, that partner generally has the stronger claim, even if both people paid toward it for years. If a dispute happens, unmarried partners generally take it to civil court as a contract or property claim — not family court, which is where married couples' divorces are handled. That's a meaningfully different, and often more difficult, path.
What a cohabitation agreement actually is
A cohabitation agreement is a written contract between two people who live together but aren't married. In general terms, it can address how property and shared expenses are handled while the couple lives together, and how things would be divided if they separate.
The key distinction from a prenup or postnup: those are specifically family law instruments tied to marriage. A cohabitation agreement is generally governed by ordinary contract law, the same body of law that governs business agreements. That's actually part of what makes it powerful — courts have long enforced contracts between people who aren't married, as long as the agreement meets the basic requirements of a valid contract.
What it can generally cover
Depending on the couple's situation and state, a cohabitation agreement can generally address things like:
- How property acquired during the relationship would be divided if the couple separates
- Who is responsible for rent, mortgage payments, or other shared bills, and in what proportion
- What happens to a shared home — who stays, who moves out, how any equity is split
- How debt taken on during the relationship is handled
- Whether one partner would provide financial support to the other for some period after separating
This overlaps in spirit with the kind of thinking covered in combined or separate finances and what counts as marital property — except for unmarried couples, there's no state default system sitting underneath the agreement. The agreement generally has to do more of the work.
Palimony and the case that created the concept
The word "palimony" gets thrown around loosely, and it's worth understanding where it came from. It traces to Marvin v. Marvin, a 1976 California Supreme Court case involving actor Lee Marvin and his former partner, Michelle Marvin, who had lived together for years without marrying. The court held that unmarried partners can generally enforce express or implied agreements to share property or provide support to one another, similar in spirit to what a married couple might resolve through divorce — as long as the agreement isn't based solely on an exchange of sexual services.
Marvin opened the door to what the media nicknamed "palimony" — support one unmarried partner may seek from another after separating, based on an agreement rather than marital status. What's often left out of that story: not every state recognizes palimony claims, and among states that do, the requirements for proving an agreement existed vary significantly. Some require the agreement to be in writing. Some allow it to be implied from conduct over time, which is generally much harder to prove.
The practical takeaway is almost the opposite of what people assume. Because palimony law is so inconsistent and hard to rely on, a clear written cohabitation agreement generally matters more for unmarried couples than a prenup matters for married ones — not less. Married couples have a default system to fall back on. Unmarried couples, in most states, largely don't.
The common law marriage wrinkle almost no one accounts for
A small number of states — including Colorado, Iowa, Kansas, Montana, Texas, and Utah, along with Washington D.C. — still recognize common law marriage. Where it's recognized, a couple can generally become legally married without a ceremony or license, typically by living together, intending to be married, and holding themselves out publicly as a married couple — telling others they're married, filing joint tax returns as spouses, using the same last name, that kind of thing.
Simply living together for a long time, even for years, generally isn't enough on its own in any state. But couples in common law marriage states who behave in ways that look like a public marriage — without ever intending to actually be legally married — can find themselves unexpectedly subject to the very state divorce and property rules a cohabitation agreement might otherwise help them avoid. If you live in one of these states, this is worth raising directly with an attorney, especially if your day-to-day life could look like a marriage from the outside even though you've never had a ceremony.
Setup: Alex and Jordan, unmarried, buy a house together. Alex has better credit, so the mortgage and title are in Alex's name only. Jordan contributes $1,500/month toward the mortgage and pays for renovations out of a joint account they both use.
Without a cohabitation agreement: If the couple separates, Alex generally holds legal title to the house. Jordan would generally need to prove — through records, communications, or other evidence — that an agreement existed to share ownership, in order to have any legal claim to the home's value. That's a real dispute, not a formality, and it happens in civil court.
With a cohabitation agreement: If the couple had signed an agreement stating Jordan would receive a defined share of the home's equity in exchange for monthly contributions, that share would generally be documented and far more straightforward to enforce.
This example is hypothetical and simplified. Actual outcomes depend on the state, the specific facts, and how any agreement was drafted.
What a cohabitation agreement generally can't do
It doesn't create inheritance rights. Unmarried partners generally don't inherit from each other automatically under state law, no matter what a cohabitation agreement says about property division while both partners are alive. That requires separate estate planning — a will, updated beneficiary designations, and potentially other documents. Know Your Half's guide to financial safety nets every couple should have covers the basics of what that looks like.
It also doesn't create the tax filing status, Social Security spousal benefits, or health insurance rights that come with legal marriage. A cohabitation agreement addresses the financial relationship between two specific people — it doesn't replicate the broader legal status of marriage itself.
This conversation starts with a licensed attorney.
Whether a cohabitation agreement makes sense for your relationship — and what your state requires to make one enforceable — are questions for a licensed attorney. That's the right next step, and no website can substitute for it.
Take the Financial Alignment Quiz →The conversation matters, married or not
Everything on this page ultimately points back to the same idea that runs through this entire site: clarity now is worth more than assumptions later. Married couples build that clarity partly on top of a legal default system. Unmarried couples generally have to build it entirely on their own — through honest conversation first, and through a written agreement if they want it to hold up.
Neither path requires assuming the worst about a relationship. It just means treating a shared financial life — a home, years of contributions, a life genuinely built together — as something worth being explicit about, whether or not there's ever a wedding involved.