Like the convertible model, a combination seat grows with your child. It works as a forward-facing seat and a booster; simply remove the harness straps and use the seat belt instead when he's ready to make the switch. Kids can typically ride forward facing with a harness in a combination seat until they weigh 40 to 65 pounds (depending on the seat model) and without the harness as a booster up to 80 to 100 pounds.
1. Using the harness when your child's too heavy.
Check the manual for the harnessed weight limit. The maximum weight on the box applies to booster-mode.
2. Overlooking the height guidelines.
Your child may get taller before he gets heavier. When the harness straps are no longer above his shoulders or his ears have reached the top of the seat, use the seat as a booster. To see the proper way to install the different kinds of car seats, watch the expert videos at chop.edu/carseat.