Knowing your max heart rate can help you in dial in your training, as it guides your target training zones, cluing you in on when to step on the gas and when to pull back on your efforts.

“Heart rate training allows you to monitor your effort, to keep the easy days easy, the hard days hard, and the tempo sessions in the right ‘effort,’” says Terra Castro, the owner and founder of Detroit Body Garage. Without heart rate data, “many people spend time in this ‘gray zone,’ not getting the full benefit of the training effect,” she says. “Plus, heart rate training is also a way to make sure you aren’t overtraining and are recovering well.”

In order to execute heart rate training properly, you have to get to know your max heart rate or the highest heart rate you can attain during exercise. The catch, of course, is that knowing your max heart rate can be a little elusive to pin down.

How to Calculate Maximum Heart Rate
The most common way to find your maximum heart rate is by using one of the many age-based equations. The most well-known of these is the very simple Fox formula:

220 – age = maximum heart rate (MHR)

This means that for a 30-year-old runner, the estimated maximum heart rate would be 190. Then, heart rate zones can be determined by calculating a given percentage of the 190 MHR.

The trouble with the Fox formula is that it’s not the most accurate formula, as numerous variables affect MHR including genetics, the specific activity (MHR varies between running and cycling due to the involvement of upper body musculature), medications, body size, altitude, and yes — even age. Runners of the same age can have drastically different max heart rates depending on genetics or how well-trained they are.

Because of this, there are at least six other formulas, all claiming bragging rights for being the “most accurate” for predicting maximal heart rate.

Researchers are doing their best to validate the different formulas, but that gets tricky, too. For example, a study published in the Journal of Strength and Conditioning Research determined that in college-aged subjects, the Gellish2 and Fairburn equations seemed to be the most accurate options.

Here’s are break down on what those max heart rate formulas look like:

• Gellish2: 191.5 – 0.007 x age^2 = MHR
• Fairburn: 201 – 0.63 x age for women = MHR
  OR 208 – 0.80 x age for men = MHR
• Gellish: 206.9 – (o.67 x age) = MHR
• Tanaka: 208 – (0.7 x age) = MHR

But there’s still a problem for the general public when it comes to using these formulas: They’re just a rough estimate of MHR because differences between individuals can vary widely. For instance, a longitudinal study in the Journal of Medicine and Science in Sport and Exercise found that the older a person and the higher the person’s body mass index (BMI), the less likely it is for age-predicted maximal heart rates (like all of the formulas above) to be accurate. So studies that look at healthy, college-aged subjects, or trained athletes, or really anyone under 50 years old, may not be good predictors for other people in the general population.

So what are you to do? It never hurts to get an estimate of your heart rate max based on any of the above formulas. But from there, just start paying attention to where your heart rate tracks during workouts to see if the estimates feel accurate.

“The heart rate tolerance is specific to each individual and is best determined by experience,” says Professor William O. Roberts, a professor in the Department of Family Medicine and Community Health at the University of Minnesota. “The role of MHR for runners is to provide a guide for training. The closer you are to your MHR during your workouts and races, the shorter the duration of exercise that you’ll be able to maintain at that pace. So, if you can maintain a rate of 160 during your workouts and races, your MHR is well above that.”

Just about any GPS-tracking watch will also track heart rate with at least moderate accuracy, but if you’re looking for the most accurate option available, studies show you’ll be best served by opting for a chest-strap monitor. However, more recent research, published in 2023, found that the accuracy of a chest strap versus a wrist-worn heart rate monitor may depend on the activity, as the accuracy was similar between activities like walking and jogging, but not more intense walking (in which the chest strap is the way to go).

Another study, also published in 2023, found that popular wrist-worn heart rate monitors — including Apple Watch, Fitbit Charge, TomTom Runner Cardio, and Samsung G2 — were “reasonably accurate” at lower intensity levels, but when pushing high-intensity efforts, that accuracy went down (for efforts above 150 heart beats per minute).

How to Use Heart Rate in Training
Once you’ve selected a heart rate monitor, the trick is putting the information you glean from the watch or strap to use. After calculating your estimated MHR, determine your different target heart rate zones by multiplying your MHR by the percentage for each zone. For example, if you wanted to find 55 percent of your maximum, you multiple your MHR by 0.55.

This corresponds to different effort zones:

• Zone 1: 55 to 65 percent MHR: This is a very comfortable effort used for warmup and cooldown.
• Zone 2: 65 to 75 percent MHR: Used for the bulk of training, this relaxed effort allows you to hold a conversation.
• Zone 3: 75 to 85 percent MHR: This is a comfortably hard effort during which you can only say short, broken sentences.
• Zone 4: 85 to 95 percent MHR: Often a 5K pace, this is a very hard effort that’s sustainable, but only lets you speak a few words at a time.

Luckily, many apps help manage this calculation for you. “I love using Garmin Connect Software and Strava,” says Castro, as you’ll get zone data right in the apps.

Just remember, because heart rate maximums using age-predicted formulas are estimates, you may need to adjust your zones over time based on your own results and how each run feels. For example, if you calculate your 90-percent zone (a nearly all-out effort) to be 175, but you’re able to maintain 175 beats per minute comfortably for several minutes, your estimated max heart rate has probably been underestimated.

You may need to adjust your zones based on perceived effort at each level of intensity as time goes on and as you adapt to training, too.

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