The legal impediments to marriage are the formal barriers that stop a union from being lawfully formed or recognized: a prior undissolved marriage, a close family relationship, being below the minimum age, lack of mental capacity, duress, and certain kinds of fraud or physical incapacity. Each impediment puts a marriage in one of two categories. A void marriage is treated as though it never existed, so no court action is strictly required to disregard it. A voidable marriage stays legally valid until the person who can challenge it wins an annulment. That difference drives everything downstream, from inheritance rights to tax filings to whether delay can lock you into a marriage you wanted out of.
A Prior Undissolved Marriage
Both people must be legally single when they apply for a marriage license. If either has an earlier marriage that was never dissolved, the new union is void. It does not matter whether the parties knew. A divorced applicant generally has to produce a finalized divorce decree, and a widowed applicant an official death certificate, and clerks in most jurisdictions check these before issuing a license.
Because a bigamous marriage is void from the start, it produces none of the legal benefits of a valid union. The second spouse has no automatic inheritance rights, no standing to file jointly for federal taxes, and no claim to spousal benefits under federal programs. For someone who married in good faith with no idea their partner was still married to someone else, the outcome can be severe.
The Putative Spouse Doctrine
Several states soften that result through the putative spouse doctrine. A spouse who entered the marriage genuinely believing it was valid can share marital property rights alongside the legal spouse. Good faith is the core requirement: the putative spouse must not have known about the prior marriage at the ceremony. Not every state recognizes the doctrine, so the consequences of an unknowing bigamous marriage vary by jurisdiction.
Close Family Relationships
Every state prohibits marriage between close blood relatives, which the law calls consanguinity. Parent and child, grandparent and grandchild, and siblings (full or half) can never marry. Most states extend the bar to aunts, uncles, nieces, and nephews. These marriages are void, and criminal incest penalties can apply separately from the marriage question.
Some states also restrict marriages based on affinity, meaning relationships created by marriage rather than blood, such as between a stepparent and stepchild. Affinity rules are less uniform than blood-relationship rules.
First Cousins
First cousins are where state laws diverge most sharply. Roughly half the states ban first-cousin marriages outright. About sixteen states and the District of Columbia allow them without restriction. A handful permit them only under conditions such as genetic counseling or age and fertility requirements. A first-cousin marriage that is legal in one state can be void and potentially criminal in a neighboring one, which creates real problems when couples relocate.
Minimum Age
Eighteen is the standard age for marrying without anyone else’s permission. Historically, states allowed exceptions below that line through parental consent, judicial approval, or both, with judges weighing maturity, financial independence, and the risk of coercion.
That picture has shifted. As of late 2025, sixteen states have set the marriage age at eighteen with no exceptions whatsoever. Many other states have enacted hard floors at seventeen, below which no parental consent or court order can authorize a marriage. The reforms reflect concerns that child marriages carry power imbalances that undermine real consent.
Emancipation
In some states, a legally emancipated minor can marry without parental consent or judicial approval, treated for marriage purposes like an eighteen-year-old. This is not universal. Many states still require judicial approval for every minor regardless of emancipation, and states with hard age floors at eighteen do not carve out emancipated minors either.
The Ratification Trap
A license issued to someone below the legal minimum age usually makes the marriage voidable rather than void. The marriage remains valid unless the underage party seeks an annulment, which in most states can be filed after they reach the age of majority. But continuing to live together as a married couple after turning eighteen can ratify the marriage, cutting off annulment and leaving divorce as the only exit.
Capacity and Consent
A valid marriage requires that both people understand what they are agreeing to. Courts call this “sound mind,” and the threshold is not high: the question is whether each party grasps the basic nature of the marital relationship and the obligations it creates, such as financial responsibility and mutual support. Mental illness or a cognitive disability does not automatically bar someone from marrying. What matters is whether the specific condition prevented meaningful understanding at the moment of the ceremony.
Temporary impairment can also destroy capacity. If a party was severely intoxicated or under the influence of drugs during the ceremony and could not appreciate what was happening, the marriage is voidable. Courts focus on the moment the vows were exchanged, not the person’s general condition. Proving what someone understood during a short ceremony months or years later is often the practical obstacle.
Duress
Consent must be voluntary. A marriage obtained through threats, physical force, or coercion is voidable. Duress does not require violence. Courts have found it in threats of criminal prosecution, threats to take children away, economic pressure, and emotional manipulation severe enough to override free will. The pressure can come from a third party rather than the other spouse. Courts weigh the age, physical and mental condition, and realistic alternatives of the person pressured, and the duress must have been operating on their will at the moment of the ceremony.
Fraud
Fraud as a marriage impediment is narrower than most people assume. Not every lie justifies annulment. The misrepresentation must go to something the law treats as essential to the marriage itself. Classic examples include concealing an inability to have children, hiding a serious criminal history, or lying about one’s identity. Misrepresentations about wealth, career, or personality generally do not qualify, even if the deceived spouse would never have married had they known. The fraud must be intentional and must have induced consent to the marriage.
Physical Incapacity
An undisclosed inability to consummate the marriage can be grounds for annulment in many states. The condition must have existed at the ceremony and must typically be permanent. The marriage is voidable, so a court action is required. If the other spouse knew before the wedding, or kept living together after discovering it, the right to annul can be lost through ratification.
What Changes If a Marriage Is Invalidated
When a marriage is declared void or annulled, the legal fiction is that it never existed. For couples who filed joint federal tax returns during the years they thought they were married, this is a retroactive problem. The IRS requires amended returns for each affected open year, changing filing status from married filing jointly to single or, if eligible, head of household.1Internal Revenue Service. Publication 504, Divorced or Separated Individuals The usual refund deadline is three years from the original filing date or two years from when the tax was paid, whichever is later, but the IRS allows an exception for annulments: claims based on a court order finding no valid marriage existed may be accepted after the normal deadline.2Internal Revenue Service. 21.6.1 Filing Status and Exemption/Dependent Adjustments
Federal benefits are tied to a valid marriage as well. Social Security survivor benefits, for instance, depend on it, and a surviving spouse of a marriage found void from the beginning may lose eligibility unless a separate rule such as a deemed valid marriage or a state-recognized common-law marriage applies.3Social Security Administration. Social Security Handbook – Effect of Remarriage – Widow(er)s Benefits Health coverage through a spouse’s employer plan, pension beneficiary designations, and immigration status tied to the marriage can all unravel at the same time.
Challenging the Marriage
The process for ending an invalid marriage depends on which category the impediment falls into. A void marriage, such as one based on bigamy or incest, is a legal nullity from the start, so no court action is technically required. In practice most people still seek a court declaration of invalidity to settle property, benefits, and official records. A voidable marriage, which covers underage status, lack of capacity, fraud, duress, and physical incapacity, requires a formal annulment where the challenging party proves the specific ground.
Time Limits and Ratification
Void marriages can generally be challenged at any time, because a legal nullity cannot cure itself through delay. Voidable marriages are different. Most states impose time limits that vary by ground: fraud annulments often must be filed within a few years of discovering the fraud, and underage annulments may have short windows running from the ceremony. The sharper risk is ratification. A spouse who learns about the defect and keeps living with their partner as a married couple can be treated by the court as having cured it, leaving divorce as the only way out.
Annulment Versus Divorce
An annulment declares that no valid marriage ever existed. A divorce ends a marriage that was valid. In a divorce, courts divide marital property, may award alimony, and address custody and support. In an annulment, the legal starting point is that there was no marriage to divide, which can leave the economically weaker party with no claim to assets accumulated during the relationship. Some states apply equitable principles to property division in annulment cases, and the putative spouse doctrine covers bigamy situations in jurisdictions that recognize it. The risk of a harsh financial outcome is one reason courts treat annulment grounds strictly and require clear proof of the impediment.
One Impediment That No Longer Applies
Sexual orientation is not an impediment. Before 2015 most states barred marriages between same-sex couples, but the Supreme Court held in Obergefell v. Hodges that the Fourteenth Amendment guarantees same-sex couples the right to marry on the same terms as opposite-sex couples, and requires every state to license and recognize those marriages.4Justia Law. Obergefell v. Hodges, 576 U.S. 644 (2015) Same-sex couples face only the impediments that apply to any other couple: age, capacity, consanguinity, and the absence of a prior undissolved marriage.