It's important to get the right angle when you install your child's infant seat. Installation procedures vary from model to model, so you'll need to read and follow the instructions in the manual that came with your particular seat and car. If you are at all unsure about whether you're installing it correctly, you can have it checked by a certified child-passenger safety seat technician. (To find one in your area, call your local police department or go to the National Highway Traffic Safety Administration (NHTSA) Child Safety Seat Inspection Station Locator.)
Your rear-facing infant car seat should be tilted just enough for your baby to lay her head back comfortably, typically around 45 degrees. If she's sitting too upright, her head could drop forward cutting off her airway. However, if her head is too far back, you'll create the risk of absorbing the forces of a crash in the head, neck, and shoulders. As your baby develops more neck strength and is able to hold her head up, the seat can be in a more upright position; if her head falls forward, you'll know the seat is not tilted back enough.
Check the owner's manual for your infant seat for information about correct tilt angles and how to achieve them. Most rear-facing and convertible seats have some kind of built-in leveling device, and most also have a level indicator. Sometimes the indicator has a device such as a bubble, ball, or color that tells you when the seat is at the correct angle. In other cases there is a reference line etched or pasted onto the seat. Be sure your vehicle is on a level surface when you use the indicator. (See our infant car seat installation video.)
If you can't achieve the correct angle with the leveling device on your seat, or if your seat doesn't have a built-in leveling device, you can use a rolled towel or "pool noodle" at the crease of the vehicle seat to help position the infant seat at the correct angle.