Little ones between 20 lbs and 40 lbs will rest comfortably in the seat, snug in a 5-point harness. Then, when you're little one is not so little - between 30 lbs and 40 lbs - the harness may be removed and the Ultra CarGo becomes a belt positioning booster in which you can use one of the seats 3-belt positioner heights in combination with your car's lap/shoulder belt system to restrain your child up to a 100lbs.