Kids can generally stop using booster seats when they are at least 12 years old or have reached a height of about 4 feet 9 inches (57 inches or 135 cm), whichever comes first. The key factor is that the child can properly fit the vehicle's seat belt without the booster. The lap belt should lie flat across the upper thighs, and the shoulder belt should fit snugly across the chest without touching the neck or face. Additionally, the child should be mature enough to sit properly throughout the ride without leaning or slumping. In the U.S., many states set the legal age for booster seat use at 8 years or until the child reaches 4 feet 9 inches in height. The National Highway Traffic Safety Administration (NHTSA) recommends booster use until the child is about 4'9" tall to ensure the seat belt fits correctly. Similarly, in the UK, children must use a booster seat until age 12 or 135 cm tall. A practical way to determine if a child is ready to stop using a booster seat is to apply the "5-step test":
- The child's back and bottom are flush against the vehicle seat.
- The child can bend their knees at the seat edge.
- The lap belt lays flat and tight across the thighs, not the stomach.
- The shoulder belt fits between the neck and shoulder.
- The child can sit correctly throughout the ride.
If all of these criteria are met, the child may safely transition out of the booster seat.
