Will the seat be for everyday or occasional use? A less expensive convertible car seat with thinner padding might be perfectly fine for a grandparent's car or a sparsely used second vehicle because all car seats on the U.S. market must pass the same federal safety tests. But if you know the seat will receive heavy use, you may want a comfier seat with side-impact protection. If you'll have to move the seat from car to car, look for a seat that is lightweight and easy to install.
Do you want to use the seat from birth? With a few exceptions, most convertible car seats will accommodate babies from birth. Be sure to check minimum weight limits, harness tightness and whether the seat comes with adequate padding to support a small infant, advises Car Seats for the Littles. If you decide to use a convertible right away, note that you probably won't have the convenience of being able to detach the seat from a stay-in-car base, as with infant car seats.
How long do you plan to keep your child rear-facing? Laws vary from state to state, but the American Academy of Pediatrics now recommends keeping children rear-facing until age 2 or until they outgrow the rear-facing limits of their seats. While most convertible car seats can accommodate smaller children rear-facing until or beyond 2, parents may find they have to flip taller or heavier children forward-facing sooner than they would like. Unfortunately, looking at a seat's rear-facing weight and height limits may not tell you the whole story. Many manufacturers require you to turn your child when their head is an inch from the top of the seat's shell, which may be at a height far below the stated rear-facing limit. The CarSeatBlog has a handy table summarizing manufacturers' height and weight limits, as well as its own measurements of some popular seats' shell heights. Also check expert and parent reviews of a particular seat to see whether it may be a good pick for extended rear-facing.
Is space tight in your vehicle? You may have a smaller vehicle with a cramped backseat, or perhaps you need to fit three car seats in one row. Look for a seat with a narrow width to maximize space -- some are as slim as 15 to 17 inches across. Also consider that convertibles with taller seat shells can hog front-to-back space when installed rear-facing, so be sure the person sitting in front of the installed car seat still has enough leg room. The CarSeatBlog has a comparison chart for certain models.
Do you want to use the seat for more than one child? Like all car seats, convertible car seats expire. But manufacturers are rolling out seats with higher height and weight limits, meaning your child might be in the seat longer. This makes it especially crucial to know the expiration date if you hope to use it again. Many models expire six years after they're manufactured, but a few have longer shelf lives -- check before you buy.
In their quest to fulfill parents' desire for a car seat that does it all, manufacturers are debuting 3-in-1, or all-in-one, car seats. Notable models include the Graco Smart Seat, Diono RadianRXT and Evenflo Symphony. Like regular convertible car seats, they flip from rear-facing with a harness to forward-facing with a harness. But there's an added bonus: They become belt-positioning booster seats, too. While it's tempting to pay a premium for such a seat, experts say it's hard for 3-in-1s to do everything well -- one may be a better fit for smaller, rear-facing children but fare poorly as a booster, while another may make an excellent forward-facing seat and booster but skimp on padding for babies. Other considerations: A 3-in-1 may expire before a child is truly ready to use only a seat belt, defeating its purpose, and the prolonged wear and tear can add up.