What to know:
- A cohabitation agreement is a written contract between unmarried partners who live together that sets out who owns what, who pays for what, and how property and debts are divided if they separate; it matters because in California, for example, the state's divorce property rules do not govern what an unmarried couple acquires together.
- A typical agreement covers shared purchases, separate property, a home titled in one name, rent and mortgage splits, joint accounts, debts, pets and a breakup plan, but it cannot stand in for a will.
- Where these agreements are enforced, courts judge them as contracts, so an agreement holds up best when it is written, signed, voluntary, based on full financial information, and supported by something other than the relationship itself; Texas and New Jersey require a writing.
- States differ: California enforces contracts between unmarried partners under Marvin v. Marvin (1976), while the Illinois Supreme Court in Blumenthal v. Brewer (2016) reaffirmed that cohabitants cannot enforce marriage-like property rights.
- A cohabitation agreement does not turn into a prenup when a couple marries; couples who marry typically sign a prenup that meets their state's premarital agreement rules.
- First does not draft cohabitation agreements; when a couple decides to marry, First's Self-Serve package drafts a prenup for their state for $649 for the couple, and Lawyer Review, where it is offered, adds an independent attorney for each partner for $3,500.
Moving in together is a happy milestone, and it tends to arrive with a stack of practical questions. Whose name goes on the lease? Who covers the mortgage when one of you owns the place? Who keeps the dog if life takes a different turn? A cohabitation agreement answers those questions in writing, while everyone is getting along.
You are in good company if you are asking. The National Center for Family & Marriage Research at Bowling Green State University found that about 20.3 million people aged 15 and older were living with an unmarried partner in 2024, up from 14.0 million in 2009.
What is a cohabitation agreement?
A cohabitation agreement is a private contract between two people who live together without being married. It records how you will handle property, money and debts while you share a home, and how you will divide things if you separate. It is sometimes called a living-together agreement.
The reason it matters comes down to defaults. Married couples who divorce have state rules for dividing what they own. Unmarried couples in California do not get those rules: in Marvin v. Marvin, 18 Cal. 3d 660 (1976), the California Supreme Court held that the Family Law Act does not govern property acquired during a nonmarital relationship. Without a written agreement, a breakup can leave two people reconstructing years of payments and promises from memory.
If you are still choosing a document, our guide comparing a prenup, cohabitation agreement and domestic partnership walks through that decision. This guide stays with the cohabitation agreement itself.
What does a cohabitation agreement typically cover?
No two households run the same way, so no two agreements look alike. These are the topics worth working through together.
Property you buy together
Anything bought together, from furniture to a car, can be listed with how it is owned: equally, or in proportion to what each person paid. The agreement can also set a buyout at fair market value if you both want to keep the same item after a split.
Separate property
The agreement can confirm that what each of you owned before moving in stays yours, along with the income it earns. Marvin itself recognized that unmarried partners may agree that each one's earnings, and the property acquired from those earnings, remain the separate property of the partner who earned them.
A home in one partner's name
This is where an agreement often does its most important work. When one partner owns the home, the other may help with the mortgage, taxes or a renovation for years without any change to the title. The agreement can treat those payments as rent, as a loan to be repaid, or as a way to earn an ownership share. If you are buying a place together, our guide to buying a home before marriage covers titling choices worth discussing first.
Rent, mortgage and household bills
Some couples split housing costs evenly; others divide them in proportion to income. Write down the formula, whose name is on the lease, and what happens to the rent if one of you moves out early.
Joint accounts and debts
For a joint account, the agreement can say how much each person deposits, what it pays for, and how the balance is divided on separation. It can confirm that debts each of you brought in stay with the person who took them on, and say who reimburses whom on a loan you co-signed.
Pets
The agreement can name who keeps each pet, how vet bills are shared, and whether the other partner gets visits. Settling this while you both feel generous is far easier than settling it later.
What happens if you break up
The breakup section ties the rest together: a notice period for moving out, a timeline for selling or buying out the home, a plan for closing joint accounts, and whether either partner pays support for a transition period.
Death and inheritance
Under California's intestacy rules (the defaults for people who die without a will), an estate passes to a surviving spouse and then to children, parents and other relatives. Registered domestic partners have the same rights as spouses, but a partner who is neither married nor registered is not on that list. A promise in your agreement to leave property to each other is also hard to prove: California limits how a contract to make a will can be established (Probate Code §21700). Our guide to wills, trusts and beneficiary designations covers the documents that pass property at death.
Children
Courts decide custody based on the child's best interests, including the child's health, safety and welfare (California Family Code §3011), and even a California prenup cannot adversely affect a child's right to support (§1612(b)). Treat parenting terms as a shared plan, and expect a court to make its own decision if you separate.
What makes a cohabitation agreement enforceable?
In California, a cohabitation agreement is evaluated under ordinary contract rules, and the Civil Code lists the essentials as capable parties, consent, a lawful object, and sufficient consideration (Civil Code §1550). Four habits support those elements.
Put it in writing and sign it
Without an express contract, Marvin lets California courts look to a couple's conduct for an implied contract, which invites a dispute about what you meant. A few states require a writing outright. Texas makes an agreement made "on consideration of nonmarital conjugal cohabitation" unenforceable unless it is in writing and signed by the person to be charged (Texas Business and Commerce Code §26.01(b)(3)). New Jersey added promises of support between unmarried partners to its statute of frauds in 2010 (P.L. 2009, c. 311).
Base it on something other than the relationship
Consideration is what each side gives in exchange for the other's promise. Marvin held that courts should enforce express contracts between nonmarital partners except to the extent the contract is explicitly founded on sexual services. Keep the terms about money, property and shared costs.
Share full financial information
California treats consent obtained through fraud or mistake as not real or free (Civil Code §1567), so a partner who hid a large debt invites a challenge. Exchanging a list of assets, debts and income before signing gives the agreement sturdier footing.
Sign voluntarily, with time to think
The same section lists duress and undue influence as defects in consent. An agreement pushed across the table the night before a move can be harder to defend than one both partners reviewed over several weeks.
Independent advice helps too, though it is no longer required in New Jersey. Its 2010 amendment had made written support promises binding only with the independent advice of counsel for both parties, but in Moynihan v. Lynch, No. A-64-20 (N.J. Mar. 8, 2022), the New Jersey Supreme Court struck down that attorney-review requirement while keeping the writing requirement.
How do states treat cohabitation agreements differently?
State law on unmarried partners comes from a mix of court decisions and statutes. Four examples show the range.
California. Beyond express contracts, Marvin allows implied contracts, partnerships or joint ventures based on a couple's conduct, plus quantum meruit (payment for the reasonable value of services) or equitable remedies such as constructive or resulting trusts when the facts warrant.
Illinois. In Hewitt v. Hewitt, 77 Ill. 2d 49 (1979), the Illinois Supreme Court held that public policy, reflected in the state's ban on common-law marriage, bars unmarried cohabitants from enforcing mutual property rights rooted in a marriage-like relationship. In Blumenthal v. Brewer, 2016 IL 118781, the court held that Hewitt remains good law. The opinion contrasts two appellate cases: in Spafford v. Coats, 118 Ill. App. 3d 566 (1983), a partner who paid for vehicles titled in the other's name recovered because her claim was independent of the relationship, while in Ayala v. Fox, 206 Ill. App. 3d 538 (1990), a partner promised half the equity in a home she helped pay for was barred because her claim resembled marital rights. Based on those cases, terms tied to specific contributions appear to stand on firmer ground in Illinois than terms that mirror a marriage.
Texas. Under the state's statute of frauds, Business and Commerce Code §26.01, an agreement made on consideration of nonmarital conjugal cohabitation cannot be enforced unless it is in writing and signed by the person it is enforced against.
New Jersey. Support promises must be in writing and signed, and since Moynihan, an agreement signed without lawyers can be enforced.
Rules elsewhere differ and change over time, so confirm your own state's law before you sign.
When should you sign a cohabitation agreement?
The best time is before money starts to mix:
- Moving in. Before you sign a lease or start paying toward one partner's mortgage.
- Buying property. Before closing, so the agreement and the title tell the same story.
- Having or adopting a child. A child often changes who works and who pays for what. Unmarried parents in California can also establish parentage through a voluntary declaration of parentage, a separate step from your agreement.
- A career pause or major financial change. Leaving work, starting a business or receiving an inheritance are reasons to revisit the terms.
- Moving to a new state. Because the rules differ, check that your agreement still fits.
What are the most common cohabitation agreement mistakes?
Watch for these missteps, each of which can weaken an agreement:
- Relying on a spoken understanding. In Texas and New Jersey, it may be unenforceable without a writing.
- Using a generic template. A form written for one state may include terms another state will not enforce.
- Writing vague terms. "We'll split things fairly" leaves a court to define fair. Name the property, percentages and deadlines.
- Leaving out the home. Address title, payments and a buyout plan directly.
- Treating it as an estate plan. It does not replace a will, a trust or beneficiary designations.
- Never updating it. A new child, home or state can make old terms a poor fit.
What happens to a cohabitation agreement if you get married?
It does not automatically become a prenup. California defines a premarital agreement as one "between prospective spouses made in contemplation of marriage and to be effective upon marriage" (Family Code §1610) and sets its own signing rules: in California, the final draft must be delivered to both parties at least seven days before signing (§1615). An agreement written for living together was not drafted with those rules in mind.
Couples who marry typically sign a prenup, and a cohabitation agreement gives you a head start: you have already listed your assets and agreed on how to share costs. A prenup can also address property from your years together, such as a house bought before marriage. Our guide to what a prenup is covers the basics, and our state-by-state prenup guides explain the rules where you live.
Putting your plans in writing
A cohabitation agreement is an act of care for each other. It turns unspoken assumptions into a shared plan and gives both partners clarity about the home and the life you are building. Take your time, share the full picture, and choose terms you would both stand behind. If marriage becomes part of your plans, First helps couples make a prenup online for their state.
Frequently Asked Questions
Is a cohabitation agreement legally binding?
It can be. California enforces express contracts between unmarried partners under Marvin v. Marvin, except to the extent they are founded on sexual services, while Illinois will not enforce claims to marriage-like property rights between cohabitants. A written, signed, voluntary agreement based on full financial information stands on the firmest footing.
Does a cohabitation agreement have to be in writing?
In some states, yes. Texas requires agreements made on consideration of nonmarital conjugal cohabitation to be in writing and signed, and New Jersey requires written support promises between unmarried partners.
Does a cohabitation agreement give my partner inheritance rights?
No. In California, intestacy law passes property to a surviving spouse or registered domestic partner and then to relatives, so an unmarried, unregistered partner has no intestate share. Wills, trusts and beneficiary designations are how partners provide for each other at death.
What happens to our cohabitation agreement if we get married?
It does not automatically become a prenup. Prenups follow their own state rules, so couples who marry typically sign one, and the conversations behind the cohabitation agreement make that easier.
