How do I track my heart rate with my Fitbit device?

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 2, the range is 30-250 bpm.

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 your device doesn't track your heart rate during swims.

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.

Heart-rate zones, which are percentages of your maximum heart rate, can help you determine the intensity of your workout or activity.

How does my Fitbit device calculate my heart-rate zones?

The formula Fitbit uses to calculate your heart-rate zones is based on your device.

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Fitbit personalizes your heart-rate zones using your heart rate reserve, which is the difference between your maximum heart rate* and your resting heart rate (source).

Heart rate reserve is an indication of your overall cardiovascular fitness. While your maximum heart rate is generally determined by age, your resting heart rate can be lowered by increasing your fitness level. By lowering your resting heart rate, you can increase your heart rate reserve.

For example, if you are 45 years old and your resting heart rate is 74 bpm, here’s the math:

First, calculate your maximum heart rate and heart rate reserve.

Metric	Calculation
Maximum Heart Rate	175 bpm Common formula of 220 - age (45)
Heart Rate Reserve	Maximum heart rate - resting heart rate
Target Heart Rate Per Zone	(Percentage of maximum heart rate × heart rate reserve) + resting heart rate

Next, use your heart rate reserve to calculate your personalized heart-rate zones.

Heart-Rate Zone	Calculation
Fat Burn Zone	110 to 134 bpm Bottom of zone: (0.4 × 101) + 74 = 110 bpm Top of zone: (0.59 × 101 ) + 74 = 134 bpm
Cardio Zone	135 to 155 bpm Bottom of zone: (0.6 × 101) + 74 = 135 bpm Top of zone: (0.84 × 101) + 74 = 154 bpm
Peak Zone	156+ bpm Bottom of zone: (.85 × 101) + 74 = 155 bpm Top of zone: maximum heart rate

Note that you can see your personalized heart-rate zones on the Active Zone Minutes screen in the Fitbit app.

*Occasionally during intense exercise, you might notice your heart rate go above your Fitbit-calculated maximum heart rate.

All other devices

Fitbit estimates your maximum heart rate* with the formula of 220 - your age, and calculates your heart-rate zones based on that number (source).

*Occasionally during intense exercise, you might notice your heart rate go above your Fitbit-calculated maximum heart rate.

What are heart rate zones on my Fitbit device?

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Personalized zones adjust as your fitness level or other factors change.

Icon	Zone	Description
	Below Zones Below 40% of your heart rate reserve	Below the fat burn zone, your heart beats at a slower pace. You’re at rest for now.
	Fat Burn Zone Between 40% and 59% of your heart rate reserve	In the fat burn zone, you’re likely in a moderate activity such as a brisk walk. Your heart rate and breathing might be elevated, but you can still carry on a conversation.
	Cardio Zone Between 60% and 84% of your heart rate reserve	In the cardio zone, you’re likely doing a vigorous activity such as running or spinning.
	Peak Zone Greater than 85% of your heart rate reserve	In the peak zone, you’re likely doing a short, intense activity that improves performance and speed such as sprinting or high-intensity interval training.

Custom Zones

Instead of using these 3 heart-rate zones, you can create a custom zone to target a specific heart rate:

1. In the Fitbit app, tap the Today tab and tap your profile picture.
2. Tap Heart Rate Zones.
3. 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.

All other devices

Icon	Zone	Description
	Below Zones Below 50% of your maximum heart rate	Below the fat burn zone, your heart beats at a slower pace. You’re at rest for now.
	Fat Burn Zone Between 50% and 69% of your maximum heart rate	In the fat burn zone, you’re likely in a moderate activity such as a brisk walk. Your heart rate and breathing might be elevated, but you can still carry on a conversation.
	Cardio Zone Between 70% and 84% of your maximum heart rate.	In the cardio zone, you’re likely doing a vigorous activity such as running or spinning.
	Peak Zone Greater than 85% of your maximum heart rate.	In the peak zone, you’re likely doing a short, intense activity that improves performance and speed such as sprinting or high-intensity interval training.

Custom Zones

Instead of using the 3 heart-rate zones, you can create a custom zone to target a specific heart rate:

1. Tap the Today tab and tap your profile picture > Heart Rate Zones.
2. 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.

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 exercise, wear your device a bit tighter and higher for an improved fit. The band should be snug but not constricting (a tight band restricts blood flow, potentially affecting the heart-rate signal). 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.
  

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?

Several factors can affect your heart rate, including air temperature, stress level, alcohol or caffeine intake, immune response to illness, 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?

For any concerns about your heart-rate data, contact your physician.

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 smartwatch hardware.

To resolve common issues, see our troubleshooting steps in What factors can affect my heart-rate reading on my Fitbit device?

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.