Learn how Fitbit tracks your heart rate day and night, and see tips to get a more accurate reading.
How does my Fitbit device detect my heart rate?
When your heart beats, your capillaries expand and contract based on blood volume changes. To determine your heart rate, the optical heart-rate sensor in your Fitbit device flashes its green LEDs many times per second and uses light-sensitive photodiodes to detect these volume changes in the capillaries above your wrist. Then your device calculates how many times your heart beats per minute (bpm). The optical heart-rate sensor detects a range of 30-220 bpm.*
We use green LEDS because they maximize the signal detected from the capillaries near the surface of the skin. The optical heart-rate sensor also uses infrared light to determine when the device is on your wrist to improve the accuracy of your heart-rate data.
*This range applies during sleep; while you’re awake, the range is 40-220 bpm. On Fitbit Versa, the range is 30-250 bpm.
How do I check my heart-rate on my Fitbit device?
On most devices, swipe up on your clock face to open Fitbit Today
. See your current heart rate and either your heart-rate zone or resting heart rate (if not in a zone). Swipe to see your time spent today in each heart-rate zone and your cardio fitness score.
If your device has an Exercise app, you can check your real-time heart rate and heart-rate zone during a workout. Note that heart-rate tracking is disabled while swimming.
On Fitbit Ionic and Fitbit Versa series, the heart-rate value appears gray if your watch is searching for a stronger reading.
What are heart-rate zones?
Heart-rate zones can help you optimize your workout by targeting different training intensities. Fitbit estimates your maximum heart rate with the common formula of 220 minus your age, and calculates 3 heart-rate zones based on that number. Occasionally during intense exercise, you might notice your heart rate go above your Fitbit-calculated maximum heart rate.
For more information about zones, see the American Heart Association's Target Heart Rates article.
OUT OF ZONE
Below 50% of your maximum heart rate
Your heart rate may be elevated, but not enough to be considered exercise.
FAT BURN ZONE
Between 50% and 69% of your maximum heart rate
This low-to-medium intensity exercise zone may be a good place to start for those new to exercise. It’s called the fat burn zone because a higher percentage of calories are burned from fat, but the total calorie burn rate is lower than more intense exercise zones.
Between 70% and 84% of your maximum heart rate.
In this medium-to-high intensity exercise zone, you're pushing yourself but not straining. Most people should target this exercise zone.
Greater than 85% of your maximum heart rate.
This high-intensity exercise zone is for short, intense sessions that improve performance and speed.
Instead of using the 3 zones based on your maximum heart rate, you can create a custom zone to target a specific heart rate:
- Tap the Today tab and tap your profile picture > Heart Rate Zones.
- Enter your custom zone.
On fitbit.com, log into your dashboard and click the gear icon in the top right. Click Settings > Personal Info and enter your custom zone.
What is my resting heart rate on my Fitbit device?
Resting heart rate is the number of times your heart beats per minute when you are still and well rested. This metric can be an important indicator of your fitness level and overall cardiovascular health. The typical resting heart-rate range for adult Fitbit users is 50-90 beats per minute. Active people often have a lower resting heart rate. For more information, see the Fitbit Blog.
Fitbit uses your heart-rate data from when you’re both awake and asleep to estimate your resting heart rate. For best results, wear your device to sleep.
How do I improve the accuracy of my heart-rate reading on my Fitbit device?
As with all heart-rate tracking technology, accuracy is affected by personal physiology, device location on your arm, and type of movement.
For a more accurate heart-rate reading:
- Wear your Fitbit device on top of your wrist, and make sure the back of the device is in contact with your skin.
- When you’re not exercising, wear your device a finger’s width above your wrist bone.
- During a workout, experiment with wearing the device higher on your wrist (2 finger widths) for an improved fit. Many exercises such as bike riding or weight lifting cause you to bend your wrist frequently, which could interfere with the heart-rate signal if the watch is lower on your wrist.
- Consider tightening your wristband before a workout and loosening it when you’re done. The wristband should be snug but not constricting (a tight wristband restricts blood flow, potentially affecting the heart-rate signal).
What is my cardio fitness score?
Cardio fitness score, Fitbit's estimate of your VO2 Max, is an indicator of overall fitness that can help predict performance for endurance-based activities including running, biking, and swimming (source
). For more information, see What is my cardio fitness score?
Are the LEDs on my Fitbit device safe?
The LEDs on your device have very low power so they won't burn your skin, and they're programmed to shut down if your device freezes or can't find a signal.
Note that the LEDs continue to flash if you turn off heart-rate tracking.
Why is my heart-rate reading blank or frozen on my Fitbit device?
Occasionally your device may have difficulty getting a strong signal, especially during exercises that cause your arm to move vigorously. If your heart rate is blank or frozen, try to relax your wrist and stay still for up to 10 seconds. On Versa 2, you might also notice a spike or dip in your reading as your device finds your heart rate. In both cases, normal tracking should resume shortly.
For additional troubleshooting steps, see Why don't I see my heart rate on my Fitbit device?
Are there other factors that can affect my heart-rate reading?
Several factors can affect your heart rate, including air temperature, stress level, physical body position, and medication use (source).
Exercising in cold weather can make it more difficult for your device to track your heart rate, as environmental conditions can affect skin perfusion (the amount of blood that flows through your skin).
Spikes in your heart rate during sleep may be caused by sudden movements (for example, waking up and getting out of bed), or a weak signal due to wrist placement.
Review our tips in How do I improve the accuracy of my heart-rate reading on my Fitbit device?
For any concerns about your heart-rate data, contact your physician.
Why is there a difference in my heart-rate reading on my Fitbit device versus another device?
At times, you might notice slight variations between your heart-rate reading on your Fitbit device versus on another device (such as a chest strap or another wrist-based heart-rate tracker) due to the differences in technologies.
Differences between heart-rate readings on your device and on exercise equipment are likely due to wrist or hand position. Make sure the back of your device is in contact with your wrist and that your band is snug.
Note that you might notice slight variations in your heart-rate readings on Versa 2 as compared to readings on another Fitbit device. We optimized the algorithm used to track your heart rate on Versa 2 to complement our latest hardware.