Moving your child through the various stages of car seats can be expensive, especially with the average price of a new convertible seat hovering around $175. 

But there are trade-in events, like the one being offered by Target from Sept. 10 through Sept. 23, where you can bring in your old car seat and get up to 20 percent off the purchase of a new one.

Babies "R" Us is offering a 25 percent discount on car seats through Sept. 30 even if you don't have an old seat to trade in. And check with your local baby-product retailers to see whether they have trade-in events planned.

The key question, of course, is when to upgrade. There are various factors to consider, but parents should be careful about making the switch too soon. Your child's safety should always be the primary goal. 

Consumer Reports' car seat buying advice and ratings can help you through the process. Our child-seat testing team offers these tips to help parents decide when is the best time to upgrade.

Your child is too big for an infant seat. Many rear-facing infant seats have weight limits of 30 pounds or more, but most don’t have matching height limits. So don’t be surprised if your child outgrows the infant seat long before he or she reaches the weight limit. 

Your safest bet is to trade up to a convertible seat, which can face either the front or back of the car, and continue to have your child face the rear.  

Your child is 1 year old. Based on our most recent recommendations and tests results, if your child has reached his or her first birthday and still fits in a rear-facing infant seat, the safest move is to switch to a rear-facing convertible. 

Our newest car-seat crash-test methodology includes simulating the back of a car's front seat. In our tests, we found that a 1-year-old child was far more likely to hit its head on the back of the front seat while in a rear-facing infant seat than when riding in a rear-facing convertible seat.

Your child's car seat has expired. Many parents don’t realize that child car seats carry expiration dates. This is particularly important when you have several children and use the same car seat for each one. 

The owner's manual or seat label should tell you when the seat was built and when it should be discontinued. The lifespan is usually six years.

Expiration dates are used to make sure that key components of the seat haven’t degraded too much and that the seat meets contemporary safety standards, which are always being raised. 

Your child's seat has been in a crash. Most seats can be reused after a minor fender bender. But the National Highway Traffic Safety Administration recommends replacing a seat if it was in a collision that involved injuries or required the vehicle to be towed, the airbags were deployed, or the seat or the door nearest the seat was damaged.

If you’ve had such a crash and haven’t yet replaced the seat, a trade-in event may be a good time to do so.

Your child's car seat is damaged. Daily use, heat and cold cycles, and less than careful storage can take a toll on a car seat’s structure. Check for cracks, loose parts, and worn straps and fasteners. If the seat is damaged, it may not offer as much protection in a crash.

Even if you’re trading in for the same type of seat, one with new, undamaged components will provide better protection than a worn one will.

It’s simply time for the next step. If your child has outgrown his or her current car seat stage or is close to doing so, a trade-in event may be the best time to make the move.

But don’t rush the process, even if the savings are tempting. Other than moving from a rear-facing infant seat to a rear-facing convertible seat, other transitions may actually prove less safe for a child. For example, a forward-facing seat is less safe than a rear-facing seat, and a booster is less safe than a forward-facing harnessed seat.

If you're unsure about what to do with a retired car seat, use CR's interactive decision tree in "Can I Reuse or Donate My Car Seat?"

Use the timeline below to find the right car seat for your child. 

Consumer Reports Car Seat Timeline