You can stop using a booster seat when your child is tall enough for the car's seat belt to fit properly without it, typically when they reach about 4 feet 9 inches (57 inches) in height. This usually happens between the ages of 8 and 12 but depends more on the child's height and seat belt fit than their age. Key indicators that a child is ready to stop using a booster include:

• The lap belt lies low across the upper thighs, not the stomach.
• The shoulder belt crosses the middle of the shoulder and chest, not the neck or face.
• The child can sit all the way back against the car seat with knees bending at the seat edge.
• The child can stay seated correctly for the entire trip without slouching.

Legally, many places require children to use a booster seat until they are at least 8 years old or meet the height requirement; some jurisdictions recommend booster seats until age 12 for better safety. It's important not to rush this transition for safety reasons. In summary, the transition from a booster seat is guided primarily by the seat belt fitting properly rather than a specific age.