Does an affair affect custody? Usually very little. Learn how courts apply the child's best interests and when infidelity can actually matter.
Best for the Children Editorial·7 min read·July 22, 2025·Updated October 17, 2026
You found the messages, or you were the one who sent them. Now the marriage is ending and the question that keeps you up at night isn't about the house. It's about the kids. The short answer is that adultery, on its own, usually has little effect on custody. American custody law is built around the child's best interests, and the leading model statute tells courts to ignore a parent's conduct when it doesn't affect that parent's relationship with the child. An affair matters only to the extent it touches the children.
If you're dealing with infidelity, you're in large company. The Institute for Family Studies, using recent General Social Survey data, reports that about 20% of men and 13% of women say they have had sex with someone other than their spouse while married. These figures are self-reported, so the true numbers could differ. They also cover "ever-married" people, so they can't show whether the person who cheated stayed married.
The pattern also changes with age. Among ever-married adults aged 18 to 29, women report slightly more infidelity than men, 11% against 10%. From about age 30 the gap reverses. The highest rates show up among women in their 60s, at 16%, and men in their 70s, at 26%.
So family courts see affairs constantly. That is one reason they have settled rules for how much weight an affair gets, and in custody the answer is usually very little.
Much of the confusion comes from mixing up two decisions. One is whether and why the marriage ends. The other is how the children's time and care will be arranged.
On the first question, every state now allows some form of no-fault divorce. New York was the last to adopt it, in 2010. No-fault means neither spouse has to prove the other did something wrong. It is enough that the marriage has broken down. Some states allow only no-fault divorce. Others still keep traditional fault grounds, including adultery, alongside the no-fault option. Sources count the no-fault-only states differently, putting the number at 15, 16 or 17, so treat any single figure with caution.
New York shows how the fault side works. Its no-fault ground, Domestic Relations Law § 170(7), requires that the marriage has been irretrievably broken for at least six months, with one spouse stating so under oath. Adultery remains a separate ground under § 170(4), but it is hard to prove because the law requires evidence from someone other than the two spouses. The accused spouse also has defenses under § 171, including that the other spouse forgave the adultery, consented to it, or waited more than five years after discovering it.
Even where adultery can be a reason for ending the marriage, that does not make it a reason to change custody. Fault in the marriage and fitness as a parent are judged separately. That is also why it is wrong to say that courts in no-fault states "can't consider" an affair at all. In any state, conduct can come up in a custody case if it bears on the child.
Custody decisions across the U.S. rest on the child's best interests. The Uniform Marriage and Divorce Act, a model law that shaped many state statutes, makes this the standard in § 402. It also adds a limit that matters a great deal here. The court must not consider the conduct of a proposed custodian if that conduct doesn't affect the custodian's relationship to the child. The factors the Act lists are not mandatory and not exhaustive, so judges keep broad discretion.
State statutes put this standard in their own words:
None of these lists asks whether a parent was faithful to their spouse. They ask how each parent has cared for the child and how they will care for the child in the future.
Because the test is the child, an affair becomes relevant only where it connects to parenting. The examples below are not rules from a statute. They show how the best-interests standard tends to be applied, and the outcome always depends on the facts of the case and the state's law.
Even in these cases, the court is weighing how the parent behaved toward the child. The affair is background.
Ontario is sometimes cited in articles on this topic, but it is a Canadian province with its own law. Its Children's Law Reform Act also decides custody and access on the child's best interests. Practitioners read the Act to mean that a parent's past conduct counts only if it is relevant to their ability to act as a parent. The Act separately allows courts to consider violence or abuse against a spouse, a parent of the child, a member of the household, or any child. The principle is close to the American one: the affair itself isn't the question, the parenting is.
The following is practical advice rather than law:
Adultery can end a marriage, and in states that keep fault grounds it can be the legal reason for the divorce. In custody, though, it usually counts for little. Judges ask which arrangement serves the child, and they are generally directed to set aside conduct that doesn't affect the parent's relationship with that child. An affair matters only when it reaches the children, through exposure, risk, neglect or abuse.
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