Sometimes our users have issues with heart rate (HR) zones — different apps and fitness trackers show inconsistent data:

The left screenshot is from an app called Zones. It put the first 8 minutes of the workout into the Warm-up zone and the other 37 minutes into the Fat burn.

On the right, Welltory’s zones count almost the entire workout as cardio, though the heart rate is the same in both apps.

We understand how frustrated and confused you might feel right now.

Keep reading to learn why these HR zones fail to match.

Deeper dive:

This might seem obvious, but the heart rate zones depend on the formula a specific app or device uses.

Welltory applies the formula* that uses your personalized maximum HR and recent resting HR alongside your training intensity:

* We calculate your maximum HR using a regression equation to predict HR max in healthy adults. This equation was proved to be accurate in the meta-analysis of 351 studies involving 18,712 subjects. Then, we compare it to your maximum HR within the last year and go with the greater value.

A lot of devices calculate your maximum HR as 220 − your age in years. Then, they multiply the result by the target HR range value — 0.6 for 60% of your functional capacity, 0.7 for 70%, etc., completely ignoring your resting HR.

For example, Polar uses this formula to determine the zones — we’ve checked it on their HR zone calculator page:

The Zones app also pays no attention to your resting HR whatsoever:

We’ve examined some trustworthy studies and realized that the "220 − age" formula has nothing to do with personalized HR zones.

In a recent study published in the NCBI, researchers at the University of Illinois, Chicago tested a total of 4,796 healthy subjects and proved that the "220 − age" formula (age-predicted maximum heart rate (APMHR) below) is useless in predicting the actual response to exercise because of its inaccuracy:

Another study suggests that "it is clear that the traditional equation overestimates HRmax in young adults, intersects with the present equation at age 40 years, and then increasingly underestimates HRmax with further increases in age".

And here is one more study, where the authors managed to undermine the credibility of the “220 − age” formula in support of the Karvonen formula that we use:

The authors of another study published in the International Journal of Medical Research & Health Sciences also think that your resting HR is a relevant factor in determining training zones. The researchers evaluated the relation between maximum HR and resting HR in three groups: non-athletes, athletes, and people with type II diabetes. They concluded that exercises affect your resting HR significantly, and ignoring it is a bad idea:

Thus, the "220 − your age" formula won’t get you anywhere close to the accurate HR zones without your personalized maximum and resting HR.

The Karvonen formula takes your resting HR on board. That’s why our results are more accurate and personalized. The authors of an article published in BC Medical Journal concluded that this formula works fine for estimating your exercise intensity:

Some athletes also get frustrated by the Polar and Garmin HR ranges.

For example, one 43-year-old female marathoner needed to build up her aerobic base.

She bought smart gadgets to track her heart rate and started the HR training. Those gadgets calculated her heart rate range for zone two as 108–125 beats per minute (bpm). Two months later, the marathoner found that she can only stay within the range if she is walking briskly or jogging at 12–13 min/mile.

This "HR training" made her suffer a lot because the HR zone was too low for her fitness level. Besides, those two painful months destroyed her previous efforts, and now she finds it hard to run faster.

Out of despair, she turned to other runners asking for help:

Moreover, the marathoner had to calculate the appropriate HR zones on her own. It turned out that the HR range for zone two is 128–139 bpm for her, which is drastically higher than those calculations provided by Polar and Garmin.

We don’t know her recent resting HR and can't get her maximum HR within the last year, but we can calculate the zones using our formula.

The calculations would look as follows:

55 + (0.6 [208 − 43*0.7 − 55]) = 128 bpm and

55 + (0.75 [208 − 43*0.7 − 55]) = 147 bpm.

So, the intensity of our zone two is way higher than 108–125 bpm calculated by Polar and Garmin.

If the marathoner had worked out with Welltory, she wouldn’t have had to calculate the zones on her own, lose all her progress, and wonder what had gone wrong. We’d have taken care of all these things.

She wouldn’t have had to torture herself with the exhaustingly slow pace either because our HR zones are higher, so the running speed would have been more comfortable, too.

We take your age, resting HR, fitness level, and then follow these six steps to calculate your zones. Note that HR zones have nothing to do with your gender.

1. First, we determine your maximum heart rate using the formula:

2. After that, we compare the result with your maximum HR within the last year (if we have it) and use the greater value.

3. Then, we figure out your resting HR as follows:

3. Then, we calculate the lower HR value for the light zone (40 percent) using the formula:

Resting HR + (0.4 [maximum HR − resting HR]), where 0.4 stands for 40% of your functional capacity.

And the upper value for the light zone (50 percent):

Resting HR + (0.5 [maximum HR − resting HR])

4. Now, we’re going to find your target heart rate for the fat burn zone:

Your lower HR value is:

Resting HR + (0.5 [maximum HR − resting HR])

And the upper HR value is:

Resting HR + (0.6 [maximum HR − resting HR])

5. Finally, we use the same formula to calculate your HR ranges for other zones with the functional capacity factors of 0.75 and 0.85.

Let’s say you are a 30-year-old man, and your resting HR is 50 bpm, and maximum HR is 190 bpm. Your HR ranges for zones 1–5 will then be as follows:

* Note that each person is unique. If these explanations do not match how you feel, keep a log of your symptoms — you might want to discuss them with your doctor at your next appointment.

We’ve decided to combine the last two zones starting at 80% of intensity for several reasons.

First, if you are looking for a challenge, the best way to improve your anaerobic threshold is to train at about your anaerobic threshold heart rate. This threshold heart rate sticks around 80–85% of your functional capacity, which is also known as the "lactate tolerance zone". This zone conditions the body to buffer or withstand the high acidosis and shuttle away the lactic acid to be resynthesized.

Second, the presence of lactic acid leads to high levels of acidosis and subsequently affects muscle cell enzymes. That is, the enzymes that are responsible for aerobic metabolism are sabotaged, and your aerobic endurance capacity is hurt. Repeated days of high-intensity red lining results in damage to these enzymes, and you simply can’t train aerobically without problems.

Third, the "pure" Red Line zone of 90–100% is a pretty dangerous place to hang out. The feeling of dizziness, or feeling close to hyperventilating, may creep up on you out of nowhere. This study found evidence that extremely high-intensity exercise can acutely increase the risk of sudden cardiac arrest or heart rhythm disorders, especially for those who have heart diseases.

If you are still not convinced, check out this story of John Mandrola. He is a 46-year-old athlete who was training like a demon for the USA Cycling Championships and ended up with atrial fibrillation because of exercising to extremes.

Plus, high zone training can downgrade the immune system because it results in the body's physiological response, which produces an increase in stress hormones such as cortisol. Stress hormones decrease the activity of certain immune cells (T cells and NK cells), which are responsible for directly killing invading microorganisms. Therefore, your resistance against infectious agents is compromised by high-zone training.

To help you make your workouts as effective as possible, we offer one Peak zone starting at the most advantageous high-intensity level — 80% of your functional capacity. However, we’d like you to remember that moderate exercise is still the best prescription for good physical and mental health.

Some Garmin devices allow to customize your heart rate zones. For example, you can enter your maximum and resting heart rates manually and select the base to view and edit your heart rate zones as a percentage of your maximum heart rate, a percentage of your heart rate reserve (maximum heart rate minus resting heart rate), or a percentage of your lactate threshold heart rate. It's important to note that the manual input of maximum and resting heart rates increases the possibility of making a mistake. The results will be more accurate if these metrics are calculated automatically on the basis of your data.

Polar uses the following formula by default:

For a 30-year-old man with a resting HR of 50 bpm, it will calculate your bpm range for zone two (60–70%) as follows:

(220 − 30)*0.6 = 114 bpm — your lower HR value

(220 − 30)*0.7 = 133 bpm — your upper HR value

Thus, your HR range for zone two will be 114–133 bpm.

Let’s do the same thing with the Karvonen formula and the regression equation we use at Welltory:

50 + (0.6 [208 − 30*0.7 − 50]) = 132 bpm — your lower HR value

50 + (0.75 [208 − 30*0.7 − 50]) = 153 bpm — your upper HR value

And your HR range for zone two will be 134–148 bpm.

As you can see, the difference is enormous: 114–133 bpm by Polar vs. 132–153 bpm by Welltory. Plus, Welltory’s zones are self-adjustable to your resting HR. As your fitness improves, the intensity of each zone will increase automatically. Thus, Welltory gives you the HR zones that work best for your current fitness level, so your workouts could pay off faster.

If you are an athlete, the wrong intensity of your zones can ruin all the progress you’ve made — just like it happened with that marathoner above.

If you want to exercise at the right intensity adjusted daily, track your zones in our app. And let these fitness trackers and other apps keep an eye on something else: your heart rate, blood pressure, and breathing cycles.

If you use an Apple Watch model running a watchOS 9 or newer to track your workouts, the Welltory app can show not only time, heart rate, calories, and other standard metrics but also your personalized heart rate zones adjusted in real time. You can read more about it here.