Yes, adopting an 18-year-old is legal in every state, and the process is far simpler than adopting a minor. Because the adoptee is a legal adult, biological parents have no say, a home study is not usually required, and many cases wrap up in a single court hearing within weeks of filing. What deserves careful thought is what the adoption changes afterward: inheritance rights shift, some benefits open up, and a few things people expect it to do — like conferring immigration status — it simply does not do.
Who Can Adopt and Be Adopted
Every state permits adult adoption, but eligibility rules vary. Roughly two-thirds of states let any adult adopt any other adult. The remaining third impose restrictions, most commonly a minimum age gap. California, Nevada, Utah, South Dakota, Georgia, and New Jersey require the adopter to be at least 10 years older than the adoptee. Idaho requires 15 years. Check your own state’s rule before you file, because a petition that fails the age-gap test will be denied on its face.
Spouse consent almost always matters. If either party is married, many states require written consent from the adopter’s spouse and the adoptee’s spouse before granting the petition. Adoption creates legal family ties that affect both spouses’ inheritance and financial obligations, so a refusing spouse can generally block the process unless the court finds exceptional circumstances.
Courts also look at why you want to do this. An adoption between romantic or sexual partners will be denied in many jurisdictions. New York case law has held that adoption statutes cannot be used as a substitute for marriage to formalize a sexual relationship. Roughly half of states treat a sexual relationship between an adoptive parent and adult adoptee as incest, with criminal penalties attached. Courts want to see a genuine parent-child or family purpose behind the petition.
How the Court Process Works
Adult adoption starts with a petition filed in the court that handles adoptions where you or the adoptee live. Depending on how your state organizes its courts, that could be probate court, family court, circuit court, district court, or superior court.1GovInfo. Court Jurisdiction and Venue for Adoption Petitions The petition includes names, ages, and addresses for both parties, along with a written statement of consent from the adoptee.
You do not need consent from the adoptee’s biological parents. Once someone turns 18 there are no parental rights left to terminate, so biological parents have no legal standing to block the adoption. A handful of states require that biological parents receive notice of the proceeding, but notice is not consent. They cannot veto it.
After filing, the court schedules a hearing. Both parties generally need to appear. The judge reviews the petition, confirms that consent is freely given, and evaluates whether the adoption serves a legitimate purpose. If everything checks out, the judge issues a final decree of adoption, giving the adoptee the same legal status as a biological child, including inheritance rights and the option to take the adopter’s surname.
Without a home study, a waiting period for parental rights termination, or interstate compact paperwork, many adult adoptions go from filing to decree in a matter of weeks.
What It Costs
Court filing fees for an adult adoption petition generally range from about $100 to $350, depending on the jurisdiction. If you handle the paperwork yourself, that may be your only hard cost. Many adult adoptions are straightforward enough for self-representation, especially when both parties consent and there are no complicating factors.
Hiring a family law attorney adds to the total. Fees for an uncomplicated adult adoption commonly run from a few hundred dollars to around $1,500. Contested adoptions, interstate filings, or cases with estate planning complexity can push costs higher. You should also expect a separate fee from your state’s vital records office for the amended birth certificate.
One thing that will not offset those costs: the federal adoption tax credit does not apply here. The credit requires the adopted person to be under 18 or physically or mentally incapable of self-care.2Internal Revenue Service. Adoption Credit Adopting a healthy 18-year-old does not qualify. Employer-provided adoption assistance programs carry the same age limit. The expenses are entirely out of pocket.
How Adoption Changes Inheritance Rights
This is the consequence people most often overlook. Once the decree is issued, the adoptee gains full inheritance rights from the adoptive parent under intestate succession. If the adoptive parent dies without a will, the adoptee inherits the same share a biological child would.
The flip side catches people off guard. In most states, adoption severs the legal parent-child relationship with the biological family. The adoptee may lose the right to inherit from biological parents, grandparents, and other biological relatives under intestate succession. A Virginia Supreme Court case illustrated this when adult grandchildren lost their right to inherit from their grandmother after their mother was adopted out of the family at age 53. The adoption cut the entire biological line.
Some states carve out exceptions, particularly for stepparent adoptions, where the adoptee may keep inheritance rights from the non-adopted biological parent. But the default rule in most states is that adoption replaces one set of legal family ties with another. If the biological family has existing wills or trusts that reference “children” or “descendants,” the adoption could also change whether the adoptee qualifies under those terms. Talk to an estate planning attorney before filing, not after.
Health Insurance and Social Security
Under the Affordable Care Act, employer-sponsored and individual health plans that offer dependent child coverage must make it available until the child turns 26. The law does not condition eligibility on financial dependency, school enrollment, or residency.3U.S. Department of Labor. Young Adults and the Affordable Care Act: Protecting Young Adults and Eliminating Burdens on Businesses and Families FAQs A legally adopted child qualifies the same as a biological child, so an adopted 18-year-old can potentially join the adoptive parent’s health plan and stay covered until 26.
Social Security works similarly. A legally adopted child may qualify as a dependent on the insured parent’s record for child’s insurance benefits. If the adoption happens before the parent becomes entitled to old-age or disability benefits, the adopted child is considered dependent automatically. If the adoption occurs afterward, additional dependency requirements apply during the parent’s lifetime, though dependency is presumed if the adoptee applies after the parent’s death.4Social Security Administration. 20 CFR 404.362 – When a Legally Adopted Child Is Dependent
Social Security child’s benefits generally end at 18, or at 19 if the child is still in secondary school full-time. Disability benefits for an adult disabled child are available only if the disability began before age 22. Adopting an 18-year-old primarily opens a path to survivor benefits if the adoptive parent dies, not an immediate monthly check.
What Adult Adoption Will Not Do
It will not create immigration benefits. Under federal immigration law, for an adopted person to qualify as a “child” for family-based green card petitions, the adoption must have occurred before the child turned 16.5Office of the Law Revision Counsel. 8 U.S. Code 1101 – Definitions A narrow sibling exception allows adoption before age 18, but only when a biological sibling was already adopted from the same family before age 16. Adopting someone at 18 falls outside every window. The adoptive parent cannot file a family-based immigrant petition on the adoptee’s behalf. USCIS’s guidance on adult adoptees addresses only people who were adopted as children and are now adults, not people first adopted in adulthood.6U.S. Citizenship and Immigration Services. Adult Adoptees and U.S. Citizenship If immigration is part of the motivation, this is not a path forward.
Amended Birth Certificate and Name Change
After the final decree, the court sends a report to the state vital records office where the adoptee was born. The original birth certificate is sealed, and a new amended certificate is issued listing the adoptive parents. The process works the same for adults as for children, and the amended certificate becomes the official legal birth record for all purposes, including passports and driver’s licenses.
Most state vital records offices issue the amended certificate within four to twelve weeks. Delays of six months or longer can happen when information is incomplete, fees go unpaid, or the adoptee was born in a different state than where the adoption was finalized, because the paperwork has to travel between jurisdictions.
A name change is optional, not automatic. The adoption decree may include the new surname, but you will still need to update your Social Security card, driver’s license, bank accounts, and any professional licenses. Each licensing board has its own process, and some will not issue an updated license until your next renewal.
Weighing the Decision
Adult adoption often formalizes a relationship that already feels like family: a stepparent who raised you, a foster parent, a mentor, a close family friend. Making it legal can carry real emotional weight for both sides.
The decision also ripples outward. Existing family members may react strongly. Biological parents may feel replaced, even without a legal role. Other children in the adoptive family may worry about inheritance or their place in the family. These conversations are worth having before filing, and a family therapist who works with blended or non-traditional families can help both sides think through the consequences before they become permanent.
Because they largely are permanent. A few states allow an adult adoptee to petition for reversal, but the process is uncommon, fact-specific, and not guaranteed. Treat the decision with the weight it carries.