Child Car Seat Safety & Compatibility Calculator

How to determine car seat compatibility?

The right car seat mode—rear-facing, forward-facing, or booster—is determined primarily by your child's physical growth relative to the manufacturer's height and weight limits. Manufacturers set these boundaries based on the structural integrity of the seat and its ability to protect the child during a crash.

Formula: Safety = MIN(Manufacturer Limit, State Law, AAP Guidelines)

Using the safety calculator: an example

Consider a 3-year-old child who weighs 35 lbs and is 38 inches tall. While the child is technically old enough for a forward-facing seat, we must check if they still fit within the safer rear-facing parameters.

Step-by-step calculation:

• Check weight against rear-facing max: If the seat's rear-facing limit is 40 lbs, the 35 lb child should remain rear-facing.
• Verify age for forward-facing harness: Confirm the child meets the minimum age requirement (usually 2+ years) before transitioning.
• Confirm height clearance: Ensure the child's head is at least 1 inch below the top of the seat shell for rear-facing mode.

Frequently Asked Questions

When do I switch to a booster seat?

Switch to a booster when your child outgrows the weight or height limit for their forward-facing 5-point harness seat. This usually happens between 40 and 65 pounds.

Do car seats expire?

Yes, car seats generally expire 6–10 years after manufacture. Materials like plastic can degrade over time, and safety standards evolve, making older seats less effective.

Can I use a second-hand seat?

Only use a second-hand seat if you are certain of its history, including that it has never been in an accident, is not expired, has no missing parts, and has no active recalls.