How to Properly Fit Your Baby in an UPPAbaby Infant Car Seat

How do I know if my baby fits properly in their car seat? When should I remove the infant insert? How tight should the harness be?

If you’ve asked yourself any of these questions, you’re not alone. Babies grow and change quickly, and knowing when to adjust their car seat fit can sometimes feel overwhelming.

The good news is that checking your baby’s fit doesn’t have to be complicated.

With an UPPAbaby infant car seat, there are a few key fit points to check each time you buckle your baby in, from harness height and headrest position to crotch buckle placement, chest clip position, and harness snugness.

While your baby’s height and weight are important, checking how your baby fits in the seat helps you confirm they are properly positioned and securely harnessed.

And when it comes to the infant insert, weight alone can’t tell you when it’s time to remove it — but fit can.

Here’s what to look for when checking your baby’s car seat fit.

LEARN MORE: UPPAbaby Infant Car Seat Fit Guide

Start With the Proper Recline

Before buckling your baby in, make sure your infant car seat is installed at the proper recline angle according to the instructions for your specific UPPAbaby car seat. The correct recline helps position your baby properly and supports your newborn’s head and airway. Always use the recline angle indicated for your specific seat.

Check the Headrest and Harness Height

For UPPAbaby infant car seats, the headrest and harness work together to create a secure fit. Adjust the headrest so the harness is at or just below your baby’s shoulders.

As your baby grows, check the harness height regularly and adjust it as needed. Babies grow quickly, especially in the first few months, so a harness position that fits your newborn may need to be adjusted sooner than you think!

Look at your baby from the side. The harness should come from the seat at or just below their shoulders, and the harness webbing should lie flat against their body.

UPPAbaby infant car seats, including the Aria V2 and Mesa V3, feature adjustable headrests with no-rethread harnesses, making it easy to adjust the harness height as your baby grows — even while they’re seated in the carrier. It’s a game changer!

Does My Baby Need an Infant Insert?

Not every baby needs the infant insert.

If you’ve been wondering, “Does my baby need an infant insert?” or “When should I remove it?” the answer comes down to your baby’s individual fit and the instructions for your specific UPPAbaby infant car seat.

The infant insert is designed to help smaller babies achieve proper positioning and harness fit. While each model has its own guidelines for insert use, the insert isn’t required for every baby. But here’s the important part: weight alone doesn’t tell you whether your baby needs it or when it should come out. Fit does.

As your baby grows, continue checking their fit to determine whether the insert is still needed. Always check the instructions for your specific car seat for exact insert guidance.

How Do I Know When to Remove the Infant Insert?

To determine whether your baby still needs the infant insert, check their overall positioning and harness fit without it.

Here’s what to look for:

• • Your baby’s bottom and back are fully against the car seat.

• • The harness straps are at or just below your baby’s shoulders.

• • The harness lies flat across the top of your baby’s legs without slack or twists.

• • The crotch buckle sits snugly against your baby’s pelvis, and your baby is not sitting on top of it.

• • The chest clip is positioned at armpit level.

• • The harness is snug and passes the pinch test at the shoulders.

If your baby meets these fit criteria without the insert, it is not needed. And remember that some babies may never need the infant insert.

LEARN MORE: When to Use the UPPAbaby Infant Insert

How to Properly Fit Your Baby in a Car Seat

Once you’ve determined whether your baby needs the infant insert, adjust the headrest so the harness straps are at or just below your baby’s shoulders. Then, start at the bottom and work your way up to secure the harness.

1. Position Your Baby All the Way Back in the Seat

Make sure your baby’s bottom and back are fully against the car seat, not scooted forward. This provides the proper starting position for securing the harness.

2. Check the Shoulder Harness Height

For UPPAbaby infant car seats, the headrest and harness work together to create a secure fit. Adjust the headrest so the harness is at or just below your baby’s shoulders.

3. Buckle Baby and Remove Slack

Buckle your baby in and check that the harness lies flat across your baby’s legs, without twists. Make sure the crotch buckle sits snugly against your baby’s pelvis and that your baby isn’t sitting on top of the crotch buckle.

Before tightening the harness, pull the harness webbing up toward your baby’s shoulders to remove any slack around the legs.

4. Tighten the Harness

Lower the chest clip, then tighten the harness so it lies snugly against your baby’s body.

5. Position the Chest Clip

Once the harness is snug, secure the chest clip and raise it to armpit level.

6. Check Harness Tightness

Make sure there is no slack in the harness around your baby’s legs. Then, perform the pinch test at your baby’s shoulders. Try to pinch a fold of harness webbing between your fingers. If you can pinch a fold, continue tightening until you can no longer pinch a fold of webbing.

Where Should the Car Seat Chest Clip Go?

The chest clip should be centered on your baby’s chest, with the top of the clip at armpit level. It should not be positioned too high near the neck or too low on the abdomen.

How Tight Should Car Seat Straps Be?

The harness should fit snugly against your baby’s body, with no slack around the legs or shoulders. A properly tightened harness should pass the pinch test at your baby’s shoulders.

Quick Fit Check

Before every ride, make sure:

• • The harness straps are at or just below your baby’s shoulders.

• • Your baby’s bottom and back are against the back of the seat, without slouching.

• • The harness lies flat, without twists or slack.

• • The chest clip is at armpit level.

• • The harness passes the pinch test over the shoulder.

Also remember: There should be at least 1 inch of clearance between the top of your baby’s head and the top of the headrest.

Making these checks part of your routine can help you feel more confident every time you buckle your baby in.

What If I’m Still Not Sure My Baby Fits Correctly?

Sometimes you can read every guide, watch every video and still think: “But does my baby actually fit correctly?” That’s completely understandable. Car seat fit is personal to your child, and it can change as they grow. If you’re unsure, you don’t have to figure it out alone.

UPPAbaby offers complimentary virtual consultations with certified Child Passenger Safety Technicians (CPSTs) who can help walk you through your baby’s fit and answer questions about harness positioning, the infant insert and adjustments as your baby grows. Just schedule an appointment to connect with us!

You can also visit the UPPAbaby Car Seat Center for additional resources, including installation guidance, fit guides, manuals and how-to videos.

A Proper Fit Starts With Knowing What to Look For

Getting your baby into their car seat can become second nature, but it’s worth taking a few extra seconds to check the fit every time.

Start with the basics: Position your baby. Adjust the headrest and harness. Buckle them in. Remove slack. Tighten the harness. Position the chest clip. Perform the pinch test.

And as your baby grows, check again. Because when it comes to your baby’s car seat, fit — not weight alone — is what matters.