monitoring heart with apple watch

How Accurate Is Apple Watch Heart Rate?


Billy Hughes
August 14, 2021

If you want to start monitoring your heart rate during exercise, you might decide to purchase an Apple Watch.

This device will keep you updated on your heart rate so you can make the most of your workouts.

How is heart rate connected to exercise? By knowing your heart rate during exercise, you can better plan your workouts. If you’re using the right intensity for your body, you’ll prevent fatigue while working towards your fitness goals. 

But, is the Apple Watch’s heart rate monitor accurate? Let’s find out. 

How Does The Apple Watch Heart Rate Monitor Work? 

how apple watch heart rate works

To know if your Apple Watch is accurate, you first have to know how it works.

Basically, Apple Watch makes use of photoplethysmography, which is based on the fact that blood is red in color as a result of how it reflects red light and absorbs green light.

The watch therefore uses green LED lights and light-sensitive photodiodes that are located on the watch casing in an area that makes contact with your skin in order to measure your blood flow. As blood flows through your wrist, the LED lights’ green light is absorbed.

The more blood that flows, the more blood is being pumped by your heart, so you’ll have a higher heart rate. By flashing its lights, the watch can calculate how many times your heart beats per minute.

The optical heart sensor also makes use of infrared light. This is when Apple Watch measures your heart rate in the background and it’s used when the watch gives you notifications about your heart rate.  

The Heart Rate app on Apple Watch means you can check your heart rate at any time throughout the day. Simply open the app and let the watch take a measurement of your heart rate. You’ll also be able to view your breathing, workout, walking, resting, and recovery rates.

If you want, you can turn on heart rate notifications. This will let you know when your heart rate is either below or above a certain number of beats per minute.

When you work out and use the Workout app, the watch will measure your heart rate throughout your workout and also for a few minutes after your workout so that you can see your workout recovery rate.

So, How Accurate Is Apple Watch Heart Rate Monitor? 

When studied in 2016, the Apple Watch was found to be one of the most accurate heart rate monitors, beating popular competing brands like Fitbit Charge HR, Basis Peak, and Mio Fuse.

In another study, this time conducted in 2019, it was found that the Apple Watch heart rate monitor could measure users’ heart rates with clinically acceptable accuracy during exercise in patients who had cardiovascular disease. 

What About Scanning Your Heart For Abnormalities? 

Scanning Your Heart For Abnormalities

The Apple Watch Series 4, 5, and 6 have electrodes in their design that are located at the back of the watch and in the watch’s Digital Crown.

These are used to measure the electrical signals in your heart when you use the ECG app or Heart Rate app. How the process works is that when you put your finger on the Digital Crown, it produces a closed circuit between both your arms and your heart, which enables the watch to capture electrical impulses in your chest.

But, does this really work to alert you to heart problems, such as atrial fibrillation? A study has shown that the Apple Watch has a good amount of sensitivity when detecting abnormal arrhythmia, but it was found to be more accurate when used by older people. However, the accuracy when it comes to detecting atrial fibrillation is approximately 40 percent. 

There are also some risks associated with using a watch that will monitor your heart rate for any abnormalities. Some medical professionals have warned consumers about overdiagnosis with the ECG functionality in Apple Watches.

This is because most people who wear smartwatches are usually young and healthy, while atrial fibrillation is more common in older members of the population. Therefore, if you’re young, fit, and healthy, you might end up experiencing regular false alarms that could result in excessive worry or overtreatment for no good reason. Although it can be accurate, the Apple Watch isn’t meant to replace a medical device.

That said, it could help to save your life. You might have heard the story about Jason Saucier, a 45-year old man from Florida who hadn’t been feeling like himself but didn’t realize he was facing a health crisis until his Apple Watch sounded an alarm that he hadn’t heard before.

He glanced down at his watch and saw that it was suspected he had atrial fibrillation. This is because the watch alerts users to a high heart rate and lets them know if their heart rhythm is abnormal and could be a symptom of atrial fibrillation.

Saucier soon started experiencing shortness of breath and became pale, which made him go to the hospital where he discovered he was about to go into cardiac arrest. 

How You Can Increase Apple Watch Accuracy

How You Can Increase Apple Watch Accuracy

How you use your Apple Watch will affect how accurate it is when working to keep you healthy. Make sure you do the following to keep it as accurate and consistent as possible.

  • Ensure the watch fits you snugly. If the watch isn’t tightly secured to your wrist, this will cause it to give you incorrect and inconsistent readings. This is because the watch won’t be making constant contact with your skin, which is required for accurate measurements.
  • Clean it regularly. If you’re sweating a lot during exercise, this can cause moisture to build up behind the watch and it will affect the sensors’ sensitivity. Therefore, it’s important to wipe the back of the watch regularly with a microfiber cloth.
  • Don’t exercise in cold conditions. If you’re exercising in cold conditions, this can alter your skin perfusion and give you an inaccurate reading. Skin perfusion is basically how much blood can flow through the skin.
  • Be wary of your tattoos. If you’ve got tattoos on your arm where the watch’s sensors make contact with your skin, this could potentially also affect the watch’s accuracy. The reason for this is because the ink and patterns on your skin could block light from the sensor. If you have tattoos on one of your wrists, it might therefore be a good idea to wear the watch on your other wrist. Just make sure that you wear it so that the watch’s Digital Crown is on the side of the watch nearest to the top of your wrist. 
  • Rethink your workout. If you’re engaging in workouts that involve irregular movements, like boxing, you won’t get as much of an accurate reading as compared to doing an exercise like running or cycling that has rhythmic movements.
  • Make sure the “Wrist Detection” feature is enabled. If you haven’t enabled the “Wrist Detection” feature on your Apple Watch, this means your background heart rate measurements won’t be taken. This includes your walking and resting rates. To ensure that this feature is enabled, open the Apple Watch app on your iPhone. Choose the “My Watch” option, then select “Passcode.” Check that “Wrist Detection” is on.
  • Don’t go into “Power Saving Mode”. If you’ve got “Power Saving Mode” turned on during a workout, this will essentially switch off the heart rate sensor. Go to your Watch’s “Settings,” then choose “Workout.” You’ll be able to see if “Power Saving Mode” has been enabled.
  • Check your privacy settings. If you’ve turned off the “Heart Rate” option in your privacy settings, this will prevent the watch from being able to measure your heart rate. Go to the “Apple Watch” app on your iPhone, and select “Privacy” to see if your “Heart Rate” option is on or off. 

Related Questions

Does the Apple Watch Series 6 measure blood oxygen levels?

The Apple Watch Series 6 does indeed monitor your blood oxygen levels via its Blood Oxygen app.

How does the Blood Oxygen app work? 

The watch has an updated optical heart sensor that provides blood oxygen measurements. When you take your blood oxygen measurement, the back crystal shines red and green with its LED and infrared light on your wrist so photodiodes can measure the light that gets reflected back. 


If you have an Apple Watch, you might be interested in using it to monitor your heart rate during exercise.

In this article, we’ve looked at just how accurate the heart rate monitor is on Apple Watch and what you can do to increase its accuracy, so you can stay on top of your fitness and health. 


Billy Hughes

Billy Hughes is a fitness trainer based out of New York. She has registered success in training clients at multiple fitness centers and thus aims to establish her module relevant to the post-pandemic era. Her space,, is an attempt towards encouraging and educating more people on the scope of indoor fitness. She believes the power of fitness can transform attitude, personality, and way of living. She also finds it rewarding to help people achieve their goals and make their lives better.