E.W.
There is a weight limit, although I don't know what it is, because both my daughters hit the length limit WAAAAY before weight limit. The length limit for an infant carrier is 26"; my younger was out of hers before 5 months. We have used the Evenflo Triumph convertible seat for both of them and we have really, really loved it (and quite a bit cheaper than Britax, but still very good quality and very safe). Your specific car seat's manual should also tell you length/weight limits, if you have it. The 26" length limit that I mentioned is in reference to the Graco Snugride infant carrier; I have no idea if different carriers have different limits, so you'll need to check with yours. But, if you do'nt still have your manual, you should be able to look on the manufacturer's website, because most brands will have their manuals and weight/length limits online.