Having an affair is not a federal crime, and in most of the country it is not a state crime either. So if you are asking whether it is illegal to have an affair, the short answer is: usually no, but the legal consequences can still be significant. Roughly 16 states keep criminal adultery statutes on the books, a divorce court can use the affair against the cheating spouse in a majority of states, a few states let the betrayed spouse sue the affair partner directly, and military service members face their own set of rules that civilians do not.
States That Still Treat Adultery as a Crime
As of 2026, about 16 states still have enforceable criminal adultery laws. Most classify it as a misdemeanor. A few treat it as a felony, with potential prison time measured in years and fines reaching $10,000.
The trend is clearly in the other direction. New York repealed its adultery statute in 2024, and Minnesota did the same in 2023. More states are expected to follow over the next decade.
Prosecutions are extraordinarily rare even where the statutes survive. District attorneys have little appetite for these cases, juries have little patience for them, and constitutional privacy concerns hang over any attempt to enforce them. Rarely enforced, however, is not the same as repealed. In a handful of jurisdictions, an adultery charge remains technically possible.
How an Affair Affects a Divorce
The real legal consequences of an affair almost always show up in divorce court, not criminal court. About two-thirds of states still allow fault-based divorce, where one spouse points to specific misconduct as the reason the marriage failed. Adultery is one of the most commonly used fault grounds, alongside cruelty and abandonment.1Legal Information Institute. Fault Divorce
Every state also offers a no-fault option, where neither spouse has to prove wrongdoing. In a purely no-fault case, the affair carries no direct legal weight. Many divorcing spouses go the no-fault route even when infidelity occurred, because fault proceedings take longer, cost more, and require airing private details in open court.
Property Division and Dissipation of Assets
In an equitable distribution state, a judge divides marital property based on fairness rather than a strict 50/50 split. Adultery by itself does not automatically tilt the scales. Spending marital money on the affair, however, often does.
Courts call this “dissipation of marital assets.” If one spouse funneled shared funds into hotel rooms, gifts, trips, or rent for a partner, the other spouse can ask the court to account for those losses. Bank statements, credit card records, and similar evidence typically do the work. When a court finds dissipation, it usually compensates the innocent spouse with a larger share of what remains. The adjustment is not framed as punishment, but it can shift tens of thousands of dollars or more depending on how lavishly the affair was funded.
Alimony
Adultery’s effect on spousal support varies widely by state. In some, a spouse who committed adultery can be barred from receiving alimony entirely. In others, the affair is one factor the judge weighs alongside income disparity, length of the marriage, and each spouse’s earning capacity. In strictly no-fault alimony states, the affair has no bearing on support.
The effect runs both ways. A financially dependent spouse who had the affair may lose a claim to support. A higher-earning spouse who had the affair may face a larger or longer alimony obligation.
Child Custody
Custody is decided on the best interests of the child, not on which spouse behaved worse during the marriage. An affair alone almost never determines who gets custody. It can enter the analysis when the surrounding circumstances actually affected the children, such as leaving young children unsupervised or exposing them to a chaotic string of new relationships. The court is evaluating parenting, not punishing infidelity.
Can You Be Sued by Your Spouse’s Partner’s Spouse?
In a small number of states, yes. The betrayed spouse can sue the person who had the affair with their husband or wife. These claims, known as “alienation of affection,” are a surviving branch of older “heartbalm” torts. To win, the suing spouse generally must show a genuine marriage existed, that the love and affection within it were destroyed, and that the third party’s conduct was a significant cause.
A related claim, “criminal conversation,” exists in some of the same states. The name is misleading; it is a civil lawsuit, not a criminal charge. It only requires proof that the third party had sexual intercourse with the married person.
Verdicts can be enormous. One widely reported case produced $2.2 million in compensatory damages and $6.6 million in punitive damages against the affair partner. Even when a case never reaches trial, the threat of one creates real leverage in divorce negotiations. Most states abolished these claims decades ago as invasions of personal privacy, but where they survive they are a serious and often underappreciated risk for anyone involved with a married person.
Infidelity Clauses in Prenups and Postnups
Some prenuptial and postnuptial agreements include infidelity clauses that impose specific financial penalties if a spouse has an affair. Typical terms include a lump-sum payment to the faithful spouse, a bump in the cheating spouse’s alimony obligation, or a shift in how property is divided. Penalties ranging from a flat $50,000 payment to $40,000 per year of marriage are not uncommon in high-net-worth agreements.
Enforceability is another matter. Few courts have ruled directly on these clauses, and the results have been mixed. Some have refused to enforce them on public policy grounds. Others have upheld them as legitimate contract terms between consenting adults. The law in most states allows spouses to agree to almost anything in a marital contract that does not violate public policy, but where infidelity clauses fall on that line remains unsettled. Treat such a clause as a negotiating tool with uncertain legal backing, not a guaranteed payout.
Military Members Face a Different Standard
Service members are the one group for whom an affair can clearly produce criminal consequences in practice. Under the Uniform Code of Military Justice, extramarital sexual conduct is a punishable offense under Article 134, the UCMJ’s general article.2United States Army. Legal Separation, Adultery and the UCMJ The offense was historically called adultery in military law and was renamed and broadened in 2019 to cover a wider range of sexual conduct than intercourse alone.
To be chargeable, the conduct must be prejudicial to good order and discipline, or bring discredit upon the armed forces. Commanders routinely weigh factors like whether the affair involved another service member’s spouse, whether it disrupted unit cohesion, and whether it reflected poorly on the military.
Maximum punishment is severe: a dishonorable discharge, forfeiture of all pay and allowances, and confinement for up to one year. Many cases are resolved through non-judicial punishment under Article 15 rather than a full court-martial, but even that outcome can end a military career. A legal separation from a spouse provides a defense under the current rules, but only if the parties are formally legally separated. Being informally “separated” offers no protection.2United States Army. Legal Separation, Adultery and the UCMJ
The Cost of Actually Proving It
Choosing to litigate adultery, rather than simply divorcing on no-fault grounds, carries its own price. Proving fault or dissipation often requires a private investigator, with hourly rates commonly running from $75 to over $200 depending on region and complexity. Financial records, depositions, and trial presentation all add attorney hours a no-fault divorce would never incur. The defending spouse faces mirror-image costs, including expert testimony and sometimes forensic accounting to counter dissipation claims. Before going down that road, both sides should be clear-eyed about whether the potential financial advantage is worth the expense and the public exposure of a fault-based proceeding.