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).
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.
Swipe left from the clock face until you reach the Heart rate tile. The tile displays your current heart rate and a graph of your recent heart rate. Tap the tile to get more details in the Fitbit Today app .
When you use the Fitbit Exercise app 
Swipe right or left from the clock face until you reach the heart rate tile. The tile displays your current heart rate, a graph of your heart rate over the past 4 hours with your lowest and highest heart rate indicated, and your daily resting heart rate.
When you use the Exercise app
Swipe up on your clock face to show your current heart rate and either your heart-rate zone or resting heart rate (if not in a zone).
If your device has an Exercise app, you can check your real-time heart rate and heart-rate zone during a workout.
Important: If your heart rate seems incorrect or is missing from your device, refer to What factors can affect my heart-rate reading on my Fitbit device for troubleshooting tips.
Heart rate tracking is turned on by default. If you turned heart-rate tracking off, turn it back on:
- On your device, open the Settings app
Heart Rate.
- Tap to turn the setting on.
Resting heart rate is the number of times your heart beats per minute when you’re still and well-rested. Typically, resting heart rate ranges from 60-100 bpm, but the rate can vary based on age and fitness level.
Why should I track resting heart rate in the Fitbit app?
Resting heart rate can be an important indicator of your fitness level and overall cardiovascular health. In general, active people often have a lower resting heart rate because their heart muscle is in better condition and doesn’t need to work as hard to maintain a steady beat.
How is resting heart rate different from sleeping heart rate?
Your sleeping heart rate is detected continuously throughout the night, and is often lower than your resting heart rate, which is estimated each day. Learn more about your sleep data and sleeping heart rate.
How do I check my resting heart rate?
To check your current resting heart rate, swipe up from the clock face on your device. To check your resting heart trends, use the Fitbit app:
- In the Today tab
in the Fitbit app on your phone, tap the Health Metric tile. Your resting heart rate is listed as one of your metrics.
- Tap the Trends tab and swipe up to find the Resting Heart Rate (RHR) to check the graphs of your resting heart rate over the course of a week, month, or year.
- In the Week view, tap Learn more below the graph for an even better understanding of how this metric is calculated.
in the Fitbit app on your phone, tap the Health Metric tile. Your resting heart rate is listed as one of your metrics.For more information, refer to What should I know about health metrics in the Fitbit app?
- Press the crown, swipe up to the Fitbit Today app
, and tap the app to open it.
- Swipe to the Resting Heart Rate card, then tap the card to get more details (if you don’t see the Resting Heart Rate card, swipe left).
- Swipe down to check your average resting heart rate for the past week.
For more information, refer to What should I know about health metrics in the Fitbit app?
What factors can affect Resting heart rate?
Several factors can affect resting heart rate. Stress, alcohol or caffeine intake, or fever usually raise resting heart rate, while regular exercise or meditation can lower it. Air temperature and certain medications can also affect resting heart rate.
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.
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 |
|---|---|
|
Moderate Zone (Fat burn on some devices) |
114 to 134 bpm Bottom of zone: (0.4 × 101) + 74 = 114 bpm Top of zone: (0.59 × 101 ) + 74 = 134 bpm |
| Vigorous Zone (Cardio Zone on some devices) |
135 to 159 bpm |
| Peak Zone | 160+ bpm Bottom of zone: (.85 × 101) + 74 = 160 bpm Top of zone: maximum heart rate |
You can check your personalized heart rate zones on the Active Zone Minutes screen in the Fitbit app:
- From the Today tab
- Swipe up. Your personalized zones are listed in the "Your heart rate zones" section.
*Occasionally during intense exercise, you might notice your heart rate go above your Fitbit-calculated maximum heart rate.
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 the Heart-rate zones on my Fitbit device?
Personalized zones adjust as your fitness level or other factors change.
| Zone | Description |
|---|---|
|
Light Zone (Below Zone on some devices) Below 40% of your heart rate reserve |
Below the moderate zone, your heart beats at a slower pace. You’re at rest for now. |
|
Moderate Zone (Fat Burn Zone on some devices) Between 40% and 59% of your heart rate reserve |
In the moderate 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. |
|
Vigorous Zone (Cardio Zone on some devices) Between 60% and 84% of your heart rate reserve |
In the vigorous 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 in the Fitbit app to target a specific heart rate:
- From the Today tab
- In the Preferences section, tap Heart rate.
- In the Exercise section, tap Heart Rate Zones.
- Tap the toggle or box next to Custom Zone and enter your custom zone.
- From the Today tab
icon.
- In the Preferences section, tap Heart rate.
- Tap Heart Rate Zones.
- Tap the toggle or box next to Custom Zone and enter your custom zone.
Heart Rate Zones and enter your custom zone.| 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 in the Fitbit app to target a specific heart rate:
- From the Today tab
- In the Preferences section, tap Heart rate.
- In the Exercise section, tap Heart Rate Zones.
- Tap the toggle or box next to Custom Zone and enter your custom zone.
- From the Today tab
- In the Preferences section, tap Heart rate.
- In the Exercise section, tap Heart Rate Zones.
- Tap the toggle or box next to Custom Zone and enter your custom zone.
Heart-rate variability (HRV) is the variation in time between heartbeats. If your heart rate is 60 bpm, your heart doesn’t necessarily beat once per second — a healthy heart isn’t like a metronome. Your autonomic nervous system determines the timing of each heartbeat.
HRV varies from person to person. Studies show that people with a higher HRV have better cardiovascular fitness and might be more resilient to stress. Mindfulness, meditation, sleep, and physical activity can help improve your HRV. A significant drop in HRV may indicate that your body is experiencing illness, stress, or depression or anxiety.
Note: This data is included in the Health Metrics tile 
Why should I track HRV?
Track your HRV in the Fitbit app to help you gauge your overall well-being. Trends in HRV data can help you be more aware of how stress and lifestyle choices, such as nutrition and exercise, can affect your body
How does my Fitbit device track HRV?
Fitbit uses the common formula called “Root mean square of successive differences” RMSSD to determine HRV from your recent heart-rate data. In the graph, your latest HRV measurement is from the longest sleep period over the past 24 hours. Only sleep periods greater than 3 hours are considered.
How do I check my HRV?
Wear your device for at least a full day, including to sleep at night. Then check your stats:
- In the morning, open the Fitbit app. On the Today tab
. Your heart rate variability is listed as one of your metrics.
- Tap Heart rate variability (HRV) to check your data in detail. These details include graphs of your data over the course of a week, month, or year.
- For details, tap Learn More above the graph.
What factors can affect HRV?
Several factors can affect HRV, including age, sex, sleep quality, stress, and lifestyle choices, such as nutrition and exercise.
Charge 5, Charge 6, Inspire 3, Sense, Sense 2, Versa 3, Versa 4, and Google Pixel Watch series notify you when your device detects that your heart rate is outside of your high or low thresholds while you appear to be inactive for at least 10 minutes.
How do I turn off heart-rate notifications on or off?
- From the Today tab
icon
- Tap High & Low Heart Rate.
- Tap the toggles to turn High heart rate notification or Low heart rate notification on or off.
icon What happens when I receive a heart-rate notification?
When your Fitbit device detects your heart rate goes above or below your personal heart rate threshold while you’re inactive, you receive a notification on your device. Tap Open, and then tap the notification in the Fitbit app to learn more about your data and complete a survey where you log any potential factors, medications, and symptoms. You can use the information you log in the survey to track your heart health trends and share it with your healthcare provider.
How do I change my heart-rate notification thresholds?
To start, your thresholds are based on your age and typical resting heart rate. To adjust your thresholds:
- From the Today tab
- Tap High & Low Heart Rate.
- Turn the toggle to turn on Custom in the High heart rate or Low heart rate section.
- Tap Threshold and choose a new threshold.
To use your default thresholds, turn off the custom threshold.
Many Fitbit devices can analyze your heart rhythm data for signs of AFib throughout the day. If you receive an irregular rhythm notification, it means that your device has detected a heart rhythm that might be indicative of AFib. For more information, refer to How do Fitbit Irregular Rhythm Notifications check for atrial fibrillation (AFib)?
On certain Fitbit devices, you can use the Fitbit ECG app to analyze a 30-second reading of your heart rhythm data for signs of AFib. For more information, refer to What is the Fitbit ECG app?
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.
Factors that can affect heart rate include 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 on How do I improve the accuracy of a heart-rate reading?
For any concerns about your heart-rate data, contact your physician.
At times, you might notice 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 may also be 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.
You might also notice variations between your heart-rate reading on new Fitbit devices compared with your old ones due to changes in the heart-rate sensor or algorithm.
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: The LEDs will continue to flash even if you turn off heart rate tracking.