TL;DR: A prenup only becomes valid when a couple marries, so unmarried couples who want protection now typically use a cohabitation agreement, which is enforced as an ordinary contract. A domestic partnership is a registered status, not a document that divides property. According to the National Center for Family & Marriage Research, roughly 20.3 million adults lived with an unmarried partner in 2024, up from about 14 million in 2009.You live with your partner, or you're about to, and someone mentioned you should "get something in writing." Then the terms started piling up: prenup, cohabitation agreement, domestic partnership. If you're unmarried and trying to figure out which one applies to you, the confusion is understandable, because these three documents get lumped together even though they do different jobs.
Living together before or instead of marriage is common. The National Center for Family & Marriage Research at Bowling Green State University, analyzing U.S. Census Bureau data, found that roughly 20.3 million adults lived with an unmarried partner in 2024, up from about 14 million in 2009. So if you're wondering how to handle money and property as an unmarried couple, you're asking a question millions of people are asking too. The good news: once you name your marriage plans, the right document usually becomes obvious.
Start with the one question that decides it Before you compare features, answer one question: are you planning to marry, planning to stay unmarried, or exploring a registered status where you live? Your answer routes you to a specific document.
If marriage is part of the plan, the document that fits is a prenup, and it takes effect when you marry. If you're living together without immediate wedding plans, a cohabitation agreement is the tool that works now. If you want access to certain marriage-like rights without marrying, and your state or city offers a registry, a domestic partnership answers that separate question. These three options apply at different moments and cover different ground.
The rest of this post walks through each one, then lays them side by side so you can find your row.
The prenup: only takes effect when you marry A prenup, short for prenuptial or premarital agreement, is a contract two people sign before marriage that sets out how assets, debts, and spousal support would be handled if the marriage ends. If you want the fundamentals, our prenup primer and our guide to what a prenup is and whether you need one cover the basics.
Here's the part that trips people up. A prenup requires marriage to take effect. Under the Uniform Premarital Agreement Act , which has been adopted by 29 states plus the District of Columbia, a premarital agreement must be in writing and becomes effective upon marriage. That last point matters for unmarried couples: a prenup does nothing until there is a marriage. If a couple signs one and never marries, it never takes effect.
So you don't have to be married yet to sign a prenup, and you don't even have to be formally engaged. But the document sits dormant until the wedding happens. If you have no plans to marry, a prenup is not the tool for your situation. That's what the next document is for.
The cohabitation agreement: the document for unmarried couples If you're living together and unmarried, a cohabitation agreement is the written contract between two unmarried people who share a home that sets out how property, debts, and expenses are handled during the relationship and if it ends. It covers the practical questions that come up when two lives are financially intertwined: who owns what, who pays for what, and what happens to shared assets if you separate.
The important distinction is how courts treat it. Most states recognize cohabitation agreements and enforce them under ordinary contract principles rather than marriage law. The landmark case here is Marvin v. Marvin , 557 P.2d 106 (Cal. 1976), in which the California Supreme Court held that unmarried couples may enter enforceable contracts about property and earnings, provided the agreement rests on something other than the relationship itself as consideration. Most states followed with their own variations. The Cornell Legal Information Institute describes cohabitation agreements as contracts analyzed under standard contract doctrine.
This matters because unmarried partners generally lack the default property protections that marriage provides. Marriage comes with a built-in legal framework for dividing assets; living together does not. Without a written agreement, there's often no automatic claim to a partner's earnings or property, no matter how long you've been together. A cohabitation agreement fills that gap on your own terms.
This comes up often for couples sharing a mortgage before marriage. If you're buying property together, our guide to buying a home before marriage walks through what to consider. For a sense of what "no agreement" looks like in practice, our post on what happens if you don't have a prenup illustrates how default state rules fill the void when nothing is written down.
Requirements vary by state, but the common threads are that the agreement should be in writing, signed voluntarily, and supported by valid consideration. Independent legal review for each partner can strengthen it. Rules differ by jurisdiction, and a few states have historically been less receptive to these agreements, so confirm the requirements where you live.
The domestic partnership: a status, not an asset agreement A domestic partnership is a legal relationship status a couple registers with a state, county, or city, and depending on the jurisdiction, it can grant some marriage-like rights, such as health-insurance access or hospital visitation. This is where a lot of posts blur the line, so it's worth being precise: registering a domestic partnership is not the same as writing a document that divides your property.
A cohabitation agreement is a private contract you and your partner write. A domestic partnership is a public registration you file with a government body. One is a document about your property and finances. The other is a status that unlocks certain rights, and it says nothing on its own about how your assets get divided if you split up.
Availability differs a great deal. Domestic partnerships are recognized statewide in only a few states, and otherwise exist through local city or county registries. The rights they carry, and even whether a registry exists where you live, vary by jurisdiction. If you want specifics, the most reliable path is to check your own state, county, or city registry directly, because the rules are local and change over time.
Domestic-partnership questions come up often for same-sex couples, and our guide to prenuptial agreements for LGBTQ couples speaks to some of those considerations. One practical takeaway: if you register a partnership and also want clear terms on property and finances, the partnership handles the status, and a separate cohabitation agreement handles the money.
Comparison at a glance Here's how the three options line up across the dimensions that decide which one fits you.
Dimension
Prenup
Cohabitation Agreement
Domestic Partnership
When it applies
Planning to marry
Living together, unmarried
Living together, want a registered status
Requires marriage to take effect
Yes
No
No (it's the status itself)
What it is
Private contract
Private contract
Registered legal status
Primarily covers
Marital asset and support terms in divorce
Property, debts, expenses while together and at separation
Access to certain rights (e.g., health insurance, visitation), varies by jurisdiction
Governed by
State marriage and premarital-agreement law
Ordinary contract law
State or local registry rules
Survives if you later marry
N/A (it's for marriage)
Generally no; sign a prenup instead
Varies; separate from any property agreement
If you read across your row, the choice usually names itself. Marriage plans point to a prenup. Living together without a wedding on the calendar points to a cohabitation agreement. Wanting a registered status points to a domestic partnership, with a cohabitation agreement alongside it if you also want property terms.
What happens when you decide to marry Say you signed a cohabitation agreement while living together, and now you're engaged. Does the old agreement carry over? Generally, no. A cohabitation agreement does not automatically survive into marriage. It was built for a different legal relationship, and once you marry, the framework governing your finances changes.
Couples who marry typically sign a prenup at that point to cover the marriage itself. Many cohabitation agreements even include a clause anticipating this, stating that the couple will create a prenup if they decide to wed. So the transition is less a surprise and more a planned handoff: the cohabitation agreement did its job while you were unmarried, and the prenup picks up when you marry.
Timing matters here, and earlier is generally better. Our guide to the best time to get a prenup explains why giving yourselves runway before the wedding tends to produce a stronger agreement and a calmer process. If you signed a cohabitation agreement with marriage in mind, that's a good moment to revisit your plans and start the prenup conversation with time to spare.
Frequently Asked Questions Do you have to be married or engaged to sign a prenup? You don't have to be engaged, but a prenup only becomes legally effective once you marry. If you never marry, the prenup never takes effect. Couples who want protection while unmarried, with no immediate wedding plans, generally use a cohabitation agreement instead, which is enforced as a contract.
What is a cohabitation agreement? A cohabitation agreement is a written contract between two people who live together but aren't married. It sets out how property, debts, expenses, and shared assets are handled while together and if the relationship ends. Courts in most states enforce it under ordinary contract principles rather than marriage law.
Is a cohabitation agreement the same as a domestic partnership? No. A cohabitation agreement is a private contract you write yourselves. A domestic partnership is a legal status you register with a state, county, or city, and it can carry certain rights like health-insurance or visitation access. One is a document; the other is a registration.
Can a domestic partnership have a prenup? Not in the prenup sense, because a prenup takes effect only upon marriage. Partners who aren't marrying can instead use a cohabitation agreement, sometimes called a living-together or domestic-partnership agreement, to spell out property and financial terms. The terms are similar; the trigger is different.
We signed a cohabitation agreement and now we're getting married. Does it still apply? Generally no. A cohabitation agreement doesn't automatically carry into marriage. Couples who marry typically sign a prenup to cover the marriage itself. Many cohabitation agreements even include a clause saying the couple will create a prenup if they decide to wed.
Are cohabitation agreements legally enforceable? In most states, yes, as long as the agreement is in writing, signed voluntarily, and supported by something other than the relationship itself as consideration. Requirements vary by state, and a few states have historically been less receptive. Independent legal review for each partner can strengthen enforceability.
Where First fits (and where it doesn't) Naming your plans is most of the work, and once you've done that, the path forward gets clear.
If marriage is part of the plan, a prenup is the document that fits, and First is built to make that part straightforward. No PDFs, no hourly rates, no back and forth with attorneys. If you're staying unmarried or registering a partnership, a cohabitation agreement or your local registry is the better path, and it's worth talking with independent legal counsel about those options. We'll be clear about that, because our product is the prenup, not the cohabitation agreement.
Either way, you can start by getting clear on which document matches your plans. If you're marrying, First can help you build a prenup on your timeline. If you're not sure yet, that clarity is the right first step, and there's no rush to decide.
Methodology The cohabitation figures in this post come from U.S. Census Bureau data and analyses of it by the National Center for Family & Marriage Research (Current Population Survey, 2009 and 2024) and the Pew Research Center (Census data, 2019 to 2023). Cohabitation counts reflect adults living with an unmarried partner, and shares reflect the cohabiting portion of all U.S. adults. Census and American Community Survey data can slightly overestimate the unpartnered population and does not capture every cohabiting relationship, so these numbers are best-available estimates rather than exact counts.
Sources First is not a law firm. The information and tools provided by First on this site are not legal advice and not a substitute for the advice of an attorney.
Cohabitation-agreement and domestic-partnership rules vary by state and locality, and enforceability is decided case by case. Confirm the requirements where you live, and treat the general information here as a starting point rather than a promise of any specific outcome.
