Adultery is not illegal in Idaho. The statute that once made it a crime has been repealed, and the old section number, 18-6601, now covers incest after a restructuring of the state’s sex crimes chapter.1Idaho State Legislature. Idaho Code 18-6601 – Incest So no, you won’t be arrested or prosecuted for an affair. But adultery still has a legal definition in Idaho’s family code and can shape a divorce in specific ways.
No Criminal Charges for an Affair
For decades, Idaho Code Section 18-6601 made adultery a crime, and it reached both the married person and the unmarried partner who knowingly had sex with someone else’s spouse. Prosecutions were essentially nonexistent long before the statute went away, and Idaho eventually repealed the criminal provision entirely. As of 2026, Idaho is not among the states that still classify adultery as a misdemeanor or a felony.
What remains is the civil definition. Idaho Code Section 32-604 defines adultery as voluntary sexual intercourse between a married person and someone other than their spouse.2Idaho State Legislature. Idaho Code 32-604 – Adultery That definition matters because it plugs directly into Idaho’s divorce grounds.
Adultery as a Ground for Divorce
Idaho allows both no-fault and fault-based divorce. Most couples file on the no-fault ground of irreconcilable differences, which requires no proof of wrongdoing. A spouse who wants the reason for the marriage’s breakdown on the record can instead file a fault-based divorce citing adultery.
The practical difference is mostly strategic. A fault filing can frame the narrative for later arguments about support or custody, but proving the affair adds evidentiary work and cost. Many people who could file on fault choose not to, because the no-fault route reaches the same divorce with less friction.
How Adultery Can Affect Spousal Maintenance
Idaho judges have discretion when awarding spousal maintenance. Under Idaho Code Section 32-705, a court may grant maintenance when the spouse seeking support lacks enough property to meet their reasonable needs and cannot support themselves through employment.3Idaho State Legislature. Idaho Code 32-705 – Maintenance The statute leaves room for the court to weigh the circumstances of the marriage.
Whether adultery moves the number depends on the facts. If a spouse drained marital funds on an affair, or the infidelity directly caused financial harm, the court has a reason to consider that conduct. A judge is not going to add alimony as punishment for cheating on its own. The focus stays on need and ability to pay.
How Adultery Affects Property Division (Mostly, It Doesn’t)
This is where the biggest misconception sits. Idaho is a community property state, and the starting presumption in a divorce is a substantially equal split of marital property. Idaho Code Section 32-712 lists the factors a court considers when adjusting that split: length of the marriage, each spouse’s age and health, income and earning capacity, liabilities, and retirement benefits.4Idaho State Legislature. Idaho Code 32-712 – Community Property and Homestead Marital misconduct is not on that list.
A judge dividing your house, retirement accounts, and bank balances is not supposed to give one spouse a larger share because the other cheated. The analysis is financial, not moral. The one indirect hook is dissipation: if a spouse spent significant community funds on the affair itself, on gifts, travel, or a separate apartment, the court can account for that spending. It’s a money issue, not an infidelity issue.
How Adultery Affects Child Custody
Custody in Idaho runs on the best interests of the child. Idaho Code Section 32-717 directs the court to make custody, care, and education decisions that serve the child’s welfare.5Idaho State Legislature. Idaho Code 32-717 – Custody of Children – Best Interest An affair by itself does not disqualify a parent or shift custody to the faithful spouse.
What can matter is behavior around the affair. A parent who brings a new partner into the home in a destabilizing way, neglects parenting duties to pursue the relationship, or exposes the child to conflict gives the court something concrete to evaluate. The question is always whether the child’s daily life, emotional security, and stability were affected.
If you’re in a custody dispute and the other parent had an affair, the persuasive move is documenting specific ways the behavior affected your child, not the moral fact of the infidelity. Judges hear “they cheated” constantly. Evidence about parenting is what carries weight.
You Cannot Sue the Other Person
Some states still let a betrayed spouse sue the third party in an affair under theories called alienation of affections and criminal conversation. Idaho does not. Both claims have been abolished, so you cannot bring a civil lawsuit against the person your spouse had an affair with. Any legal remedies run through the divorce itself.