Fitbit Charge 2 vs Fitbit Flex 2 – 11 Key Differences


It’s been a few years coming, Fitbit have refreshed their Flex and Charge line with the Flex 2 and Charge 2 devices. How do the new wearables compare against each other? Here’s a run down of the main differences between the Fitbit Charge 2 and Flex 2.

Heart Rate measured on the Charge 2

Fitbit Charge 2 - PurePulse

PurePulse on the Fitbit Charge 2

Using Fitbit’s PurePulse Heart Rate technology, the Charge 2 can calculate your heart’s beats per minute (BPM). It’s a useful metric for understanding how intense your body is working when exercising and also adds greater accuracy into your calorie expenditure tracking. Collecting data continuously around the clock allows resting heart rate to be monitored.

With heart rate data to hand, the Charge 2 also calculates a Cardio Fitness Score, which is an attempt at giving you a VO2 Max estimate without the need of visiting a sports science lab for testing.

As well as being available on the older Charge HR, PurePulse is a feature found on the Fitbit Blaze and Surge devices. The Flex 2 doesn’t feature PurePulse technology, and isn’t capable of connecting to a chest strap monitor to collect heart rate data.

Make a splash with the Flex 2

Love swimming? The Fitbit Flex 2 is water resistant to 50m so is pretty safe for showering and swimming in a pool or the sea. Fitbit even encourage use of the Flex 2 to track your swimming activity; with the SmartTrack functionality, it can automatically recognise when you’re swimming and will upload duration and calorie estimate into your Fitbit profile.

Fitbit Flex 2 - Tracks Swimming Exercise

The Charge 2 doesn’t arrive with the same levels of water proofing, so Fitbit doesn’t recommend swimming or showering whilst wearing it. It can take the odd splash though, so don’t worry about getting sweaty or jogging in the rain.

Flex 2 can’t tell the time

If you’re looking for a Fitbit which doubles up as a watch, then the Flex 2 isn’t for you. Using 5 LED lights instead of a screen means it can’t display the time on your wrist. The Charge 2 has this covered, with plenty of screen space to show you the time and your health metrics in a single view.

Charge 2 counts floors climbed

Need motivation to take the stairs over the elevator? The Charge 2  uses an altimeter sensor to detect changes in elevation. You need to climb at least 10 feet to register a floor on the device, so unfortunately stair climbers in the gym don’t get added to this total. Flex 2 doesn’t have this feature.

Charge 2 gives multi-sport options

With the Charge 2, you have the option to select activity types from the watch menu giving you the benefit of seeing real-time exercise stats on your watch as you workout. The modes covered are running, biking, weights, yoga and interval training.

When exercising, PurePulse records heart rate data at 1 second intervals, compared to 5 seconds when resting, which helps to improve the accuracy of the beats per minute collected.

Both devices come with SmartTrack, an algorithm which can automatically recognise repetitive endurance movements and attribute exercises to them, meaning the Flex 2 can track multiple sports, but won’t be able to provide feedback whilst exercising.

Charge 2 can record your running distances more accurately

If you want to know how many miles you’ve covered whist out running, the Charge 2 can use the GPS chip in your smartphone to measure distance and pace. For this to work, you have to be in range of your phone at all times, meaning you have to carry your phone with you on your run. It’s a bit of an inconvenience compared to running with GPS watch, but still has advantages over just running with your phone. For instance you can see your pace and distance data more easily in real-time as they’re displayed on the watch screen.

Using the GPS whilst out running will also provide context to the intensity of your heart rate beats per minute, enabling the collection of a more accurate Cardio Fitness Score.

Running with the Flex 2, won’t give you the ability to use GPS, as a consolation, the SmartTrack functionality will recognise that you’re running and will log duration and estimate distance.

Guided Breathing Sessions on the Charge 2

Another feature enabled by heart rate tracking, “Relax” encourages users to focus on deep breathing for a short period of time in order to lower stress levels. Choose from a two minute or five minute session and the Charge 2 will measure the variance in your heart rate to instruct you when to inhale and exhale.

To help you focus in on the task in hand, all notifications (except silent alarms) will be disabled during the brief session.

As this requires an input of heart rate data, you’ve guessed it, another feature not available on the Flex 2.

Small difference in smart notifications.

Having a Fitbit paired to your smartphone over Bluetooth allows you to receive phone notifications on your wrist. The Charge 2 and Flex 2 differ here too:

Text Notifications

Just like the Alta, the Charge 2 will allow you to read an incoming message and see sender name on your wrist. Be aware that texts that are more than a couple of lines tend to get cut off after so many characters.

With no display on the Flex 2, you won’t know whose text you or what they’ve said, but the LED lights can alert you to check your phone.

Call Notifications

The Charge 2 can also tell you the name of the caller when someone tries to ring you. Pretty useful if your phone is out of reach when working out as you can quickly glance to see if it’s someone important or a cold caller. As with texts, the Flex 2 will make you aware of an incoming call but can’t tell you who it is.

Calendar Notifications

Lastly, Fitbit Charge 2 can also bring through calendar notifications.

Different Straps

There are even differences between these two Fitbits in how they attach to your wrist! The Flex 2 opts for a peg and hole mechanism, where it pops onto your wrist and can easily be adjusted. This is similar to how the first Fitbit Flex and Alta devices fasten. It’s secure enough for walking around but with occasional knocks and contact sports is at greater risk of falling off the wrist.

The Charge 2 uses a buckle which makes the device feel more like a standard watch. This is similar to how the older Fitbit Charge’s, Blaze and Surge fasten and is generally more secure if you’re gonna get really physical.

Different Colours

Fitbit devices can be bought in a range of different colour straps. The Charge 2 arrives in Black, Plum, Teal or Blue (With a Lavender variant due to be released in the future). Flex 2 arrives in Black, Lavenda, Magenta and Navy.


Fitbit Flex 2


Fitbit Charge 2

Don’t feel like you have to commit to just one colour band. With both the Charge 2 and Flex 2, the trackers can be detached from the band; great if you’re in the mood for a different colour or just want to replace an old dirty Fitbit band.

You can even accessorise the Charge 2 and Flex 2 with different materials to give a less sporty appearance. The screen of the Charge 2 can be clipped onto leather bands, whilst the Flex 2 can slip inside a wrist bangle or worn around your neck as a pendant.

Charge 2 will cost you an extra $50

With more features available on the Charge 2, it’s no surprise that its RRP is more expensive that the Flex 2. Expect to pay around $150 for the Charge 2 and just under $100 for the Flex 2. Being new releases, both devices will also be more expensive than their original counterpart; so if you fancy saving money on a tracker expect to see the older versions fall in price.

Fitbit Flex 2 vs Charge 2 – Verdict?

Both wearables offer improvements in features and fashionable design over the original Flex and Charge HR models.

The Flex 2 is essentially more lifestyle tracker than fitness gadget. It covers the essentials to count steps and hours slept and provides the motivation to increase activity. If you want more insight into your exercise, the Charge 2 with its multi-sport modes and heart rate tracking, allows users to receive real-time feedback and get more context around their activity levels.

Compare Fitbit Prices

Fitbit Flex 2

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Fitbit Charge 2

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I'm a super keen injured runner with over 20 years experience in races and endurance training. Get in touch with me over Twitter, G+ on in the comments below.

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