A civil partnership for straight couples in the United States means registering as either domestic partners or civil union partners under state law. The arrangement gives you many of the state-level legal protections of marriage, such as inheritance rights, hospital visitation, and jointly held property, but the federal government does not treat you as married. For some opposite-sex couples that trade is deliberate; for others it quietly costs them benefits they assumed came with any committed legal relationship.
What These Arrangements Are Called in the U.S.
“Civil partnership” is the British term. In the U.S., depending on the state, you register as domestic partners or as civil union partners. The label matters less than what the state’s statute actually grants. Some states give registered partners the full set of spousal rights available under state law. Others grant a narrower slice. None of them create a marriage for federal purposes.
Only a handful of states let opposite-sex couples register at all. California, Oregon, and Washington offer domestic partnerships. Colorado, Hawaii, and Illinois offer civil unions. The District of Columbia maintains a domestic partnership registry, and Maine recognizes domestic partnerships for more limited purposes. Eligibility rules vary. California removed its earlier requirement that one partner be 62 or older, so any two adults 18 or over can register. Colorado requires both partners to be adults and unmarried.
If you live anywhere else, this option generally isn’t available to you.
State-Level Rights You Get
Within the state where you register, a domestic partnership or civil union gives you protections that unmarried cohabiting couples don’t have:
- Inheritance when a partner dies without a will. State intestacy rules typically treat a registered partner like a surviving spouse. Without registration, an unmarried partner usually inherits nothing and the estate passes to blood relatives.
- Joint property ownership with rights of survivorship, so the home or account passes to the surviving partner outside probate.
- Medical decision-making authority if your partner is incapacitated. A registered partner typically sits at the top of the surrogate decision-maker list; an unmarried partner has no automatic standing.
- Parental rights in states that grant full spousal equivalence, covering children born into or adopted during the partnership.
Colorado’s civil union statute is one of the broader examples. It extends the same rights as spouses across categories including wrongful death claims, workers’ compensation survivor benefits, hospital visitation, and the ability to adopt a partner’s child. States that go that far make civil unions functionally identical to marriage for state-law purposes. Others don’t.
What You Give Up at the Federal Level
This is where the trade-off becomes concrete. The federal government does not treat domestic partnerships or civil unions as marriages, and that cascades through every federal program.
Federal Taxes
The IRS will not treat civil unions, registered domestic partnerships, or similar relationships as marriages for federal tax purposes. You cannot file a joint federal return. Each partner files as single or, if they have dependents, as head of household.1Internal Revenue Service. Answers to Frequently Asked Questions for Registered Domestic Partners and Individuals in Civil Unions
Social Security
The Social Security Administration has indicated that some couples in non-marital legal relationships may qualify for spousal or survivor benefits under certain conditions.2Social Security Administration. Do I Qualify for Benefits as a Spouse if I Am Now in, or the Surviving Spouse of, a Civil Union, Domestic Partnership, or Other Non-Marital Legal Relationship? That guidance was written for same-sex couples in the pre-marriage-equality era and does not clearly extend to opposite-sex domestic partners. As a planning matter, don’t assume spousal or survivor benefits will be available.
Estate and Gift Taxes
Married spouses can transfer unlimited assets to each other during life or at death with no federal gift or estate tax. That unlimited marital deduction requires a legal marriage, so it doesn’t apply to domestic partners or civil union partners. If your estate is large enough to exceed the federal exemption, the difference can be significant.
Immigration
A U.S. citizen cannot sponsor a domestic partner or civil union partner for a green card. USCIS lists both relationship types among those it does not recognize as marriages for immigration purposes.3U.S. Citizenship and Immigration Services. USCIS Policy Manual Volume 6, Part B, Chapter 6 – Spouses If one of you is a non-citizen, that single fact may rule the option out.
When the Tax Trade-Off Actually Helps
The “marriage penalty” comes up often in these discussions. It’s real, but narrower than most people assume. For tax year 2026, every federal income tax bracket for married couples filing jointly is exactly double the single-filer bracket, with one exception: the top 37 percent rate. Single filers hit 37 percent at $640,600, while married couples filing jointly don’t reach it until $768,700.4Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026 For two partners each earning around $640,000, filing single keeps all of that income below the 37 percent threshold. Filing jointly as a married couple would push roughly $511,000 of combined income into the top bracket.
If your combined household income is below roughly $500,000, the federal marriage penalty is functionally zero. The brackets line up. The tax advantage of staying unmarried is largely a high-earner story.
There’s a cost on the other side that gets less attention. When an employer extends health insurance to a domestic partner, the fair market value of the employer’s contribution toward that coverage is treated as taxable imputed income on the employee’s W-2. Married spouses don’t face this. The dollar impact varies by plan, but it can run into hundreds or a few thousand dollars per year. Weigh that against any marriage-penalty savings before deciding registration is a tax win.
Employer Health Coverage Is Not Automatic
Marriage makes a spouse near-universally eligible for employer health insurance. Domestic partnership does not. Federal law does not require employers to cover domestic partners. Self-funded plans governed by ERISA can exclude them entirely, and many do. Some states require fully insured plans to cover registered domestic partners, but that mandate disappears if you move or change jobs.
If shared health coverage is a reason you’re considering registering, read your specific employer’s plan documents before deciding.
Non-Financial Reasons Couples Choose This
Not every motivation is tax or benefits math. Many straight couples prefer a domestic partnership precisely because it isn’t marriage. For couples who associate marriage with religious meaning they don’t share, a civil union or domestic partnership offers a secular legal framework. Registration is administrative. No ceremony, officiant, or vows are required.
Couples entering a second serious relationship sometimes want a legal status that feels distinct from a previous marriage. Others prefer the language itself: partners rather than husband and wife. Whether that distinction carries weight is personal, but for some couples it reflects a real preference about how they want their relationship structured.
Older couples sometimes have a practical reason. Remarriage can affect pension benefits, alimony from a prior spouse, or means-tested government benefits. A domestic partnership may preserve some of those while still giving the couple state-level legal protection. Whether it actually does depends on how each specific benefit program defines marriage and partnership, so check the program rules before relying on this.
If You Move, Your Partnership May Not Follow
Marriage is recognized nationwide. Domestic partnerships and civil unions are not. Register in California and relocate to Texas, and your partnership may carry no legal weight in your new state. Most states have no statute addressing recognition of out-of-state domestic partnerships. The portability gap affects property rights, medical decision-making authority, and even your ability to dissolve the partnership through local courts.
If relocation is a real possibility, treat this as a serious limitation rather than a technicality.
Ending the Partnership
Dissolution is not as simple as moving out. In most states it mirrors divorce, with property division, potential support obligations, and custody arrangements where children are involved. Waiting periods may apply. Contested dissolutions go through the same court system as divorces.
A few states offer a simplified administrative dissolution for partnerships with no children and limited shared assets. Outside those narrow cases, exiting a domestic partnership looks a lot like exiting a marriage, and couples who assumed otherwise are often surprised.