The weight limits for rear- and forward-facing vary greatly by car seat model. Most convertible car seats allow rear-facing to at least 30 pounds and all allow forward-facing to at least 40 pounds. Some newer car seat models allow forward-facing up to 80 pounds. The exact weight limits for each car seat model are listed on the car seat labels, usually found on the car seat sides.
Convertible car seats have two separate belt paths where the vehicle seat belt or LATCH belt can be threaded through the car seat. One of these paths is to be used when the car seat is rear-facing, and the other is to be used while forward-facing. A few car seats have a separate belt path for the LATCH belt. Double check your car seat manual and the labels on the side of the car seat to be sure you are using the correct belt path with your convertible car seat.
Thanks to higher rear-facing weight limits on convertible car seats, parents today are better able to keep their babies rear-facing to at least two years of age. As a child passenger safety technician, I recommend that parents keep their child rear-facing to the limit specified by their car seat.
The forward-facing weight limits on many convertible car seats has increased in recent years, too. I suggest that parents keep their children in a harnessed car seat as long as possible before switching to a booster seat. Today's convertible car seats make this an easier-than-ever option.