Legal capacity to contract marriage means meeting four conditions your state requires before it will recognize your union: you must be old enough, mentally able to understand what marriage is, freely consenting, and free of any existing marriage or close family relationship that would disqualify you. You demonstrate that capacity by applying for a marriage license at a county clerk’s office, where a clerk checks your identification and supporting documents and confirms no legal barrier stands in the way. Getting any element wrong can render the marriage void from the start or, in some cases, expose you to criminal liability.
Old Enough to Marry on Your Own
Nearly every state sets 18 as the age at which you can marry without anyone else’s permission. Nebraska requires you to be 19, and Mississippi sets the bar at 21. Below those thresholds, most states allow minors to marry with parental consent or a judge’s approval, though a growing number of states have eliminated all exceptions and banned marriage under 18 entirely. As of early 2025, fourteen states allow no exceptions to their minimum marriage age.
Where exceptions still exist, the rules vary widely. Some states permit 16- or 17-year-olds to marry with both parental consent and judicial approval. A handful still allow marriage as young as 15 under narrow circumstances. If you’re under 18 and considering marriage, check your state’s current law carefully. Courts increasingly scrutinize minor-marriage petitions, and judges aren’t rubber stamps. You’ll need to show the marriage serves the minor’s interest, not just the parents’ wishes.
Mental Capacity and Genuine Consent
Both people entering a marriage must understand what they’re agreeing to. The legal standard isn’t especially high. You don’t need perfect judgment or complete knowledge of marriage law. You need the ability to grasp the basic nature of the relationship, the duties it creates, and the consequences of entering it. Someone with a mild intellectual disability or a managed mental health condition can absolutely have capacity to marry. The question is whether the person understood the commitment at the time of the ceremony.
Where mental capacity gets contested, courts look at whether the person could appreciate the rights and responsibilities that come with marriage. A prior court finding that someone lacks capacity to manage their own affairs carries real weight, and if a legal guardian exists, the guardian’s consent may be required. Without it, the marriage is vulnerable to annulment. A diagnosis alone won’t invalidate a marriage, though. Courts want evidence that the condition actually prevented the person from understanding what they were doing.
Consent must also be genuine. A marriage obtained through threats, physical force, or deception about something fundamental to the relationship isn’t a real agreement. Fraud that goes to the heart of the marriage, such as lying about the ability to have children or concealing an existing marriage, can be grounds to undo the union. Pressure from family members that crosses the line from persuasion into coercion has the same effect. Whoever challenges the marriage bears the burden of proving the consent was defective.
No Existing Marriage
You cannot legally marry someone if either of you is already married to another person. A prior marriage must end through divorce, annulment, or the death of the former spouse before a new marriage can be valid. This isn’t just a paperwork technicality. Bigamy is a criminal offense in all 50 states, with penalties that range from misdemeanors carrying a few months in jail to felonies punishable by up to ten years in prison, depending on the state. Some states impose fines of $10,000 or more on top of imprisonment.
If you were previously married, you’ll need to bring proof that the marriage ended. A certified divorce decree, an annulment order, or a death certificate for the former spouse will satisfy the clerk. Don’t assume an informal separation or a long period of living apart counts. Until the legal termination is documented, the prior marriage still exists in the eyes of the law.
No Prohibited Family Relationship
Every state prohibits marriage between certain close relatives. Marriages between parents and children, siblings (including half-siblings), and grandparents and grandchildren are universally banned. Most states also prohibit marriages between aunts or uncles and their nieces or nephews. These prohibitions apply regardless of whether the relationship is by blood or, in some states, by adoption.
First-cousin marriage is where the laws diverge significantly. Roughly half of states prohibit it outright, while the rest allow it either unconditionally or with restrictions such as requiring both parties to be over a certain age or to provide proof of genetic counseling. A handful of states make first-cousin marriage a criminal offense. If you’re considering marrying a cousin, checking your specific state’s law is essential, because the rules genuinely vary from full permission to criminal penalties.
Proving Capacity at the Clerk’s Office
The marriage license is the document that officially confirms your legal capacity to marry. You apply for it at a county clerk’s office or equivalent vital records office. In most states, you can apply in any county within the state, not just the one where you live or plan to hold the ceremony. Both applicants typically need to appear in person.
Bring government-issued photo identification such as a driver’s license or passport. You’ll also need proof of age, usually a birth certificate. If either person was previously married, bring the certified document showing how that marriage ended. Most jurisdictions require Social Security numbers as well. Complete the application form carefully and make sure every detail matches your supporting documents. Inconsistencies between your ID and your application will slow things down or get your application rejected.
Fees vary by jurisdiction but generally fall in the $20 to $120 range. Some states offer a discount of up to $60 for couples who complete a premarital education course, which can also waive the mandatory waiting period where one exists. These courses cover communication skills, conflict resolution, and financial planning.
The clerk’s review is where capacity is confirmed as a legal matter. If your documents show you are of age, unmarried (or properly divorced or widowed), not closely related to your intended spouse, and appearing voluntarily, the license issues. If something is missing or inconsistent, the clerk cannot certify capacity and the application stalls until you cure the gap.
When Capacity Is Missing
Not every defective marriage is treated the same way. The law draws a sharp line between void marriages and voidable marriages, and the distinction matters more than most people realize.
A void marriage was never legally valid in the first place. Marriages involving bigamy or incest fall into this category. Because the marriage never existed as a legal matter, either spouse, a third party, or even the state can challenge it at any time. No court order is technically required to end it, though most people obtain an annulment anyway to create a clean legal record.
A voidable marriage, by contrast, is treated as valid until a court declares otherwise. Marriages where one party lacked mental capacity, was underage, or consented under duress are typically voidable rather than void. The marriage remains legally intact unless and until the affected spouse goes to court and obtains an annulment. That means a voidable marriage produces legal rights and obligations, including property rights and potential spousal support, up to the date of annulment. If neither party ever challenges it, a voidable marriage stands.
Annulment differs from divorce in one fundamental way. Divorce acknowledges that a valid marriage existed and ends it going forward, while annulment treats the marriage as though it never happened. The practical consequences can affect property division, inheritance, and even immigration status, so the distinction between “never married” and “formerly married” carries real stakes.
Capacity Without a License: Common Law Marriage
A small number of states still allow couples to become legally married without a license or ceremony. Colorado, Iowa, Kansas, Montana, Rhode Island, Texas, Utah, and the District of Columbia recognize common law marriage in some form. Several other states recognize common law marriages only if they were created before a specific cutoff date, sometimes decades ago.
Common law marriage doesn’t happen automatically just because you live together for a certain number of years. That’s one of the most persistent myths in family law. The typical requirements include a mutual agreement to be married, cohabitation, and consistently presenting yourselves to others as a married couple. Some states, like Colorado and Kansas, require both parties to be at least 18. In Texas, couples can formalize the arrangement by filing a declaration of informal marriage with the county clerk.
The same capacity rules still apply. Both parties must be of age, mentally capable of consenting, free of any existing marriage, and not closely related. A valid common law marriage carries the same legal weight as a ceremonial one, including the same rights to property division, spousal support, and inheritance. It also means you need a formal divorce to end it.