In legal terms, an adult child is a person who has reached the age of majority — 18 in most states — but is still identified as the son or daughter of their parents for purposes of family law, taxes, health insurance, and inheritance. The adult child legal definition matters because the relationship does not end at 18; it changes shape. Parents lose the authority they held during minority, but a web of federal and state rules keeps grown children and their parents financially and legally connected, sometimes for life.
What Changes at the Age of Majority
The age of majority is the birthday when the law stops treating a person as a minor. In the vast majority of states that age is 18. A few states set it at 19, and one state does not consider residents legal adults until 21. Once a person reaches that birthday, they can enter into binding contracts, sign a lease, execute a will or power of attorney, open bank accounts, and apply for credit in their own name. They can consent to their own medical treatment and become personally responsible for any debts or legal obligations they take on.
Voting rights come separately. The 26th Amendment guarantees the vote in federal and state elections at 18 regardless of a state’s majority age.1Library of Congress. U.S. Constitution – Twenty-Sixth Amendment
What Parents Lose When a Child Turns 18
Reaching the age of majority strips parents of authority they held throughout the child’s minority. The general duty of custody and care ends, and the parent can no longer make financial, educational, or legal decisions on the adult child’s behalf without specific written authorization.
Medical information is where families most often get caught off guard. Under HIPAA, health care providers cannot share an adult child’s medical records or treatment details with a parent unless the adult child signs a written authorization. This holds even if the child remains on the parent’s health insurance plan. Families who want parents to stay informed about medical care after a child turns 18 should have the adult child sign a HIPAA authorization form and a health care power of attorney.
Health Insurance Until Age 26
One of the most durable legal connections between a parent and an adult child comes from the Affordable Care Act. An adult child can stay on a parent’s health insurance plan until they turn 26. This applies to job-based plans even if the adult child is married, has their own children, is not enrolled in school, lives independently, or has access to employer coverage of their own.2HealthCare.gov. Health Insurance Coverage for Children and Young Adults Under 26 For Marketplace plans, coverage continues through December 31 of the year the child turns 26.
When an adult child ages out, COBRA may let them keep the same group coverage for up to 36 months if the parent’s employer has 20 or more employees, at full unsubsidized cost. The adult child must elect COBRA within 60 days of receiving a notice of eligibility.3Centers for Medicare & Medicaid Services. Young Adults and the Affordable Care Act: Protecting Young Adults and Eliminating Burdens on Businesses and Families Smaller employers may be covered by state continuation laws instead.
When an Adult Child Counts as a Tax Dependent
A parent who continues to support a grown son or daughter may still be able to claim that adult child as a dependent on a federal return. The IRS uses two categories.
Qualifying Child
An adult child meets this test if they are under 19 at year-end, under 24 and a full-time student, or any age if permanently and totally disabled. The parent must provide more than half of the child’s support, and the child must have lived with the parent for more than half the year.4Internal Revenue Service. Dependents
Qualifying Relative
An adult child who misses the age tests may still qualify as a “qualifying relative.” The parent must provide more than half of total support, and the child’s gross income for the year must be less than $5,200.5Internal Revenue Service. Publication 501 – Dependents, Standard Deduction, and Filing Information The child does not need to live with the parent, since children are among the relatives the IRS exempts from the residency rule.
What the Dependency Is Worth
Claiming an adult child as a dependent allows a Credit for Other Dependents worth up to $500. The credit phases out starting at $200,000 of adjusted gross income, or $400,000 for married couples filing jointly.6Internal Revenue Service. Child Tax Credit A parent who is unmarried and provides more than half the cost of maintaining the household may also qualify for Head of Household filing status, which carries a larger standard deduction and wider tax brackets than filing as single.5Internal Revenue Service. Publication 501 – Dependents, Standard Deduction, and Filing Information
Adult Children With Disabilities
When an adult child has a disability that prevents self-support, the standard rules shift significantly. Court-ordered support, federal benefits, and parental authority all extend past the age of majority — but only through specific legal steps.
Continuing Parental Support
In many states, a court can order a parent to provide financial support to an adult child indefinitely if the child cannot become self-sufficient because of a disability that began before the age of majority. These orders commonly arise in divorce cases and are calculated much like regular child support, factoring in medical expenses, daily living costs, and the adult child’s own earning ability. Enforcement tools, including wage garnishment and contempt proceedings, mirror those for standard child support.
Guardianship Does Not Happen Automatically
Parental authority ends on the child’s 18th birthday regardless of the child’s capacity. A parent who has been making medical, financial, and legal decisions throughout a disabled child’s life has no legal right to continue doing so once that child turns 18. To keep that authority, the parent must petition a court for guardianship or conservatorship. Without it, the parent cannot access medical records, manage finances, or authorize treatment. Families should begin the process well before the 18th birthday to avoid a gap.
Social Security Benefits
Two federal programs provide income to disabled adult children. Supplemental Security Income (SSI) is available based on limited income and resources. At 18, the Social Security Administration re-evaluates disability using adult rules rather than childhood rules. For 2026, an adult child is generally ineligible for SSI if they earn more than $1,690 per month, or $2,830 if blind.7Social Security Administration. Benefits for Children with Disabilities
Disabled Adult Child (DAC) benefits pay monthly income drawn from a parent’s Social Security earnings record. The adult child’s disability must have begun before age 22, and the parent must either be receiving Social Security retirement or disability benefits or have died with enough work credits. The adult child needs no work history of their own.7Social Security Administration. Benefits for Children with Disabilities
Special Needs Trusts and ABLE Accounts
A special needs trust holds assets for a disabled person without those assets counting toward Medicaid or SSI resource limits. A parent, grandparent, legal guardian, or court can establish one for a disabled individual under 65. Any funds remaining when the beneficiary dies must first reimburse the state for Medicaid payments made during the person’s lifetime.8Office of the Law Revision Counsel. 42 U.S. Code 1396p – Liens, Adjustments and Recoveries, and Transfers of Assets
ABLE (Achieving a Better Life Experience) accounts are tax-advantaged savings accounts for disability-related expenses such as education, housing, transportation, and health care. As of January 1, 2026, individuals whose disability began before age 46 are eligible, up from the previous cutoff of 26.9Office of the Law Revision Counsel. 26 U.S. Code 529A – Qualified ABLE Programs Combined contributions cannot exceed $19,000 per year in 2026, and the first $100,000 does not count toward SSI’s $2,000 resource limit.10Social Security Administration. Spotlight on Achieving a Better Life Experience (ABLE) Accounts
College Costs After Age 18
In most states, the obligation to pay child support ends at 18 or on high school graduation. A minority of states allow courts, usually in a divorce, to order a parent to contribute to an adult child’s college or vocational training costs, generally with an age cap between 21 and 23. These orders typically require full-time enrollment and satisfactory academic progress, and the same enforcement tools used for regular child support apply.
Federal financial aid works on its own clock. Most students under 24 are treated as dependents of their parents for FAFSA purposes regardless of whether a parent claims them on taxes. For the 2026–27 FAFSA, a student is independent only if they were born before January 1, 2003, are married, are a graduate student, are a veteran or active-duty service member, have legal dependents of their own, were in foster care or a ward of the court, or are an emancipated minor.11Federal Student Aid. Dependency Status Everyone else must report parental financial information, which affects aid even when parents contribute nothing.
What Adult Children Can Inherit
Adult children have no automatic right to inherit from a living parent’s estate. A parent can disinherit an adult child by writing a will that names the child and states the intent to leave them nothing. One state carves out an exception for children under 24 and for children who cannot care for themselves due to a disability, making full disinheritance of those individuals harder.
If a parent dies intestate — without a will — the rules change. Every state has intestacy laws that distribute assets in a set order, and adult children sit near the top of that order everywhere. With no surviving spouse, the adult children typically inherit the entire estate in equal shares. With a surviving spouse, children usually split a portion of the estate with that spouse. Because the specifics vary by state, parents who want control over who inherits should put a valid will in place.