Diono Monterey XT Booster Seat Review

(Last Updated On: July 9, 2021)

Diono Monterey XT in Teal.

Parents of bigger littles will understand the frustration in finding a booster seat that works for their kid.  Most boosters seem to have very narrow seat pans, making them uncomfortable for littles with larger thighs or bums.

The Diono Monterey XT, however, is a dream come true for kids who may not fit into smaller seats and for kids who prefer a more padded booster seat. It’s a hybrid of the backless portion of the Cambria and the back from the original Monterey and includes many features that make it easy to use. Best of all, our models find it quite comfortable.

CSFTL Quick Stats

  • High back booster weight range: 40 – 120 pounds
  • High back booster height range: 38 – 63 inches
  • Backless booster weight range: 40 – 120 pounds
  • Backless booster height range: 38 – 63 inches
  • Expiration: 6 years
  • Replace after a severe crash
  • Requires vehicle headrest support in both high back and backless modes
  • Must be flush against the vehicle seat back (note: this was changed in the August 2019 version of the manual, which indicate that a gap is acceptable as long as the head support is touching the vehicle seat back or head rest. If your manual indicates that the seat must be flush against the vehicle seat back and you are unable to achieve a flush installation, we recommend reaching out to Diono’s customer service for advice.)


  • Two cup holders
  • Expandable side wings
  • Lower anchor connectors
  • Can be used with inflatable seat belts


  • Highest shoulder belt guide position: 22 inches
  • Seat pan depth: 14 inches
  • Width at widest point of expandable back: 20 inches
  • Width of bottom: 17 inches
  • Width of bottom with cup holders expanded: 23 inches
  • Height with headrest fully extended: 29.5 inches
  • Weight: 13.9 pounds


Lower Anchors

Diono Monterey XT lower anchors

The Monterey XT includes lower anchor connectors. While they aren’t required for use, they do secure the booster in the vehicle when it’s not in use. They also secure the bottom portion of the booster in place when the child is climbing in and out.

The lower anchor connectors are upside down compared to the lower anchor connectors on most other car seats.  This is intentional, there’s no need to flip them over.

Adjustable Headrest and Side Wings

The Monterey XT has 11 headrest positions. The lowest booster guide position is about 15.5 inches and the highest is about 22 inches. This makes the Monterey XT suitable for a wide range of torso heights.  The headrest adjusts by simply squeezing the handle and pulling up.

Diono Monterey XT back in the narrow position.

The Monterey XT also has adjustable side wings.  Many booster seats are narrow through the torso and have a fixed width, but not the Monterey XT!  The side wings adjust with a simple twist of a dial on the back of the seat.  The manual says to adjust the width to the narrowest setting that is comfortable for the child.  The narrowest setting provides about 12.5 inches of space internally, and it can be expanded up to 14.5 inches.

Diono Monterey XT back in the widest position.

Diono boasts that the expandable back will contain shoulders up to 20 inches wide, but that’s a bit misleading — it’s actually the external width of the seat at its most expanded. Still, 14.5 inches is generous and most kids under the weight and height limits should fit well. This

The Monterey XT is quite wide, so it likely won’t work in tight three across situations, but it’s great on a captain’s chair or if you only need two seats.  The side wings are reinforced with EPS foam and aluminium.

Diono Monterey XT shoulder belt guide

The beefy belt guides on the Monterey XT also deserve a mention.  It is easy to feed the vehicle seat belt into the guide, but it’s narrow enough that the seat belt does not twist in the guide or slide out on its own, all while allowing the seat belt to freely retract when unbuckled.


Monterey XT cup holder

The Diono Monterey XT has two retractable cup and snack trays, much to the delight of my son.  When not being used, the cupholders can be folded back inside the base of the seat.  Without the cupholders, the seat measures 17 inches.  With both cupholders out, the seat measures 23 inches wide.

Padding and Cover Fabric

The Diono Monterey XT has extra foam padded throughout the seat, which contributes to the child’s overall comfort.  The cover fabric is durable and wipeable in addition to being pretty. It comes in several sophisticated colors including red, teal, heather, and purple.


The Monterey XT arrives in the box in two pieces that are easy to put together.  The directions in the manual that explain how to attach the backrest are a bit confusing. I found that if I put the bottom seat portion flat on the ground right side up, then lined up the backrest hooks and connected them to the seat, it was easy to raise the seat back portion and the seat was assembled.  I appreciate that there was no other assembly required with this seat.

Fit to Child

High Back Mode

5 Year Old

Diono Monterey XT 5.5 years old model.

Finally! A booster seat that fits this model well.  He’s 5 years old and at the top of the charts for both height and weight at 84 pounds and 47 inches tall. We have been searching for a booster for him that is comfortable, and we finally found it! His shoulders and behind are too broad for him to fit comfortably in most high back boosters, despite being within the height and weight limits.

The Monterey XT fits his frame perfectly.  We can adjust the side wings to give his shoulders more room, and the internal width of the seat pan is a generous 12.5 inches wide, giving him plenty of room to maneuver the seat belt into position and ride in comfort.  The depth of the seat is 14 inches — enough to keep even long-legged booster riders well supported.

The sides of the bottom of the seat are low enough that it’s easy for this model to get the seat belt buckled and also to get the shoulder portion of the seat belt tucked under the armrest and in proper position.

He is impressed by the comfort of the booster, and said he “loves it.” The vehicle seat belt is low across his hips, and the shoulder belt crosses right at his collarbone.

8 Years Old

Diono Monterey XT 8 years old model.

We tried our 8 year old model in the high back mode of the seat as well, and it was a great fit for her.  The lap belt was in a good spot low across her hips, and the shoulder belt crossed her collarbone nicely.  Her mom was watching as we were taking pictures, and was excited to see this seat. Her two children are at the top of the height and weight charts, and she was frustrated with their current boosters being snug. The Monterey XT has lots of growing room, though, even for bigger littles.

Backless Mode

8 Year old

Monterey in backless mode with an 8 year old model.

This model is 8 years old, weighs 100 pounds, and is 54.5 inches tall.  The Monterey XT fit her well in both modes.

The lap belt sits low on her hips and the shoulder belt makes contact with her shoulder and not her neck.  The Monterey XT comes with a seat belt adjuster for use in backless mode as needed, but this model did not need it.  She said the booster was more comfortable than the last booster she rode in.

The manual does say that the seat belt cannot touch the neck of the child: if so this seat does not fit. For most kids, the vehicle seat belt touching their neck while in a backless booster just indicates that the child should continue using the seat in high back mode until they’ve grown a bit more.


The Monterey XT’s lower anchors are not required and can only be used in vehicles where the lower anchors align directly behind the connectors on the Monterey XT.  You shouldn’t use the lower anchor connectors on a booster in a vehicle seating position with offset anchors, as the booster won’t be positioned correctly for the seat belt to fit properly.

These lower anchor connectors are attached to the seat differently from those that are used for installation on harnessed car seats.  They look like they are upside down and it will feel strange to install them this way, but it is correct.

To use the lower anchors, loosen the straps by pressing the cam lock under the front of the seat and pull the lower anchor connector out.  Attach the lower anchor connectors to the lower anchors and pull the straps to make them snug.  Because the lower anchors are not restraining the seat (the seat belt does this), there is no need to ensure there is less than an inch of movement when the seat is installed.

The manual states not to use the lower anchors if they interfere with the vehicle seat belt.

Vehicle Headrest Required

The Monterey XT requires a vehicle headrest behind it, and the booster needs to be flush against the vehicle seat back. If the vehicle head restraint pushes the booster forward, the Monterey is incompatible with that particular vehicle.

When the Seat is Outgrown

The Monterey XT is outgrown when the tops of the child’s ears are above the top of either the fully raised booster seat headrest or the fully raised vehicle headrest.

Important Information Where to Find

FAA Approval

Diono Monterey FAA prohibition label

The label on the outer right side of the backless portion of the booster has red text that says “This restraint is NOT certified for use in aircraft.”  Because airplanes use lap only seat belts, no booster seat is FAA approved for use on an aircraft.

Manual Storage

Diono Monterey manual storage pocket

The manual is stored in a cloth pouch under the cover on the bottom of the seat. It was not easy to find, however, when I first opened the box.  Typically boosters have a storage spot under the seat, and they can get a little grubby or the manual can fall out.  This storage pouch could eliminate those possibilities, but it was a little difficult to get the booklet in and out.

Date of Manufacture

Diono Montery XT Date of manufacture label

The date of manufacture label is on the bottom of the seat.  This sticker also has the model number and other important information. The manual, unfortunately, has two expiration dates printed in it. On one page it says the seat expires after six years and another page says it expires after eight years.  We reached out to Diono’s Global Safety Advocate for clarification and were informed that Diono is aware of the typo and has fixed it on their website. The older version of the Monterey is good for eight years, but the Monterey XT expires after six.


  • Can be used with inflatable seat belts
  • Many width and height choices to fit a wide range of torsos
  • Nice seat belt guide
  • Lower anchor connectors
  • Wide and deep seat pan


  • Very wide, not good for tight seating situations
  • Requires a head rest AND must be flush against the vehicle seat back

Overall Thoughts

The Monterey XT is a well-fitting option for any child who is ready to ride in a booster seat, especially those with larger builds and those who prefer some extra padding.  The Monterey XT is easy to install and use.  The lower anchor connectors, cup holders, and adjustable width make the Monterey XT uniquely customizable to fit a wide variety of passengers.  While it is bulky and won’t work well in a three across situation, the Diono Monterey XT is a great option for bigger littles and littles who prefer extra padding.

Originally written by Kristina Hocking, edits maintained by CSFTL