Quick answer
Use the seat belt fit test before leaving the booster, even if your child meets the state minimum age.
The short answer
Your child can ride without a booster when the vehicle seat belt fits correctly without help and your state law allows it. That usually means the lap belt sits low across the upper thighs or hips, the shoulder belt crosses the middle of the shoulder and chest, and the child can stay seated that way for the whole ride. CDC says proper belt fit usually happens around ages 9 to 12, while AAP notes many children do not fit most vehicle belts without a booster until ages 10 to 12.
Why age 8 is not a finish line
A lot of state laws use age 8 or a 4'9" height benchmark. Those are legal thresholds, not magic body changes. A small 8-year-old can still have the lap belt on the stomach. A tall 7-year-old may pass in one vehicle but fail in another. The honest answer is to check the law, then check belt fit in the exact seat where the child will ride.
The five checks
Ask five questions before removing the booster: can the child sit all the way back, do the knees bend at the seat edge, is the lap belt low, is the shoulder belt centered, and can the child stay like that when tired or distracted? If one answer is no, keep the booster in that vehicle.
What to do next
Start with the booster seat age guide for the fit test, then check your state law. If you are deciding after a forward-facing harness, also check whether the harness is truly outgrown before moving stages.
Before you decide
Do not make this decision from one number on a search result. Check the child restraint label, the car seat manual, the vehicle manual, and your state law. Then test the setup with the child actually sitting in the vehicle. A booster or seat belt that looks fine in theory can fit poorly in a specific back seat because belt anchors, seat depth, buckle stalks, and head restraints vary by vehicle.
If this is a legal question, start with your state page. If this is a safety question, start with the core guide linked below. The safest answer is usually the one that satisfies the law, matches the product instructions, and keeps the belt or harness positioned correctly for the full ride.
When to get hands-on help
Get help from a certified Child Passenger Safety Technician if the belt crosses the neck or face, the lap belt sits on the stomach, the booster slides around, the child cannot stay positioned, the vehicle only has a lap belt in the seating position you want to use, or you are unsure whether a forward-facing seat has been outgrown. A short in-person check can catch problems that are hard to see from a product photo or a general article.
Helpful next steps
Sources used for this topic
This article follows the same source hierarchy as the core guides: NHTSA, CDC, AAP/HealthyChildren, IIHS, federal standards, and state law pages. Check the linked core guides for the source list and state-specific notes.