Is 220 Minus Your Age Actually Your Max Heart Rate?
The number your watch flashes during a hard interval has a surprisingly shaky origin story.
This piece covers what research on age-predicted maximal heart rate formulas (220 minus age, and alternatives like Tanaka's equation) has found when tested against directly measured max heart rate, mainly in recreational runners and in exercise stress testing contexts. It does not cover wearable heart rate sensor accuracy itself, which is a separate question addressed elsewhere on this site.
Research testing the 220-minus-age formula against directly measured maximal heart rate in recreational marathon runners found the formula does not hold precisely: measured max heart rate ran lower than the formula predicted in women and higher than predicted in men. A separate look at how these age-based formulas are used in clinical stress testing raises similar doubts about treating 85% of the predicted number as a reliable checkpoint. The formula is a population-level estimate, not a measured personal ceiling.
Why that number on the treadmill display never quite feels right
You've probably seen it: punch your age into a gym console or a fitness app, and it spits back a single number, your supposed max heart rate, as if it were etched into your biology. Some people hit that number on an easy run and wonder if their heart is working too hard. Others push into a genuinely brutal interval and never get close to it. Both experiences raise the same quiet question, does a formula built on age alone actually describe what one specific chest is capable of.
That tension, between a tidy formula and a body that doesn't always cooperate with it, is exactly what researchers have gone looking for when they put the equation next to a treadmill and a heart rate monitor.
2 studies
- In a sample of recreational marathon runners who completed a graded treadmill test to measure actual maximal heart rate, the Fox formula (220 minus age) and the Tanaka formula both showed a significant difference from measured values: women's measured max heart rate ran below what both formulas predicted, while men's measured max heart rate ran above the Fox prediction.
- A review of target heart rate formulas used in exercise stress testing raises questions about the accuracy of the 220-minus-age formula and about using 85% of that predicted number as a fixed endpoint, suggesting other measurements taken during testing may carry more diagnostic weight.
What 'age-predicted' actually means in practice
The phrase age-predicted is doing a lot of quiet work in that formula. It's a population-level estimate, built to describe a general downward trend as people get older, not a personal measurement of any one heart. The marathon runner data makes that distinction concrete: heart rate did correlate with age in the group studied, but the correlation was moderate. Not tight enough that knowing someone's age lets you state their ceiling with confidence. The direction of the formula's error wasn't even consistent between men and women in that sample, and that undercuts the idea of a single universal correction factor.
Stress testing adds a separate wrinkle. Some testing settings use 85% of the age-predicted number as a stopping point or benchmark, but the review of that practice points out that failing to reach that threshold can itself be clinically meaningful in ways the simple formula doesn't capture. Other measurements taken during a test may say more about cardiovascular status than whether someone hit a percentage of a predicted number.
None of this is about whether a wearable can measure heart rate accurately in the moment, that's a different question covered in Apple Watch's heart rate accuracy. This is specifically about whether the formula being measured against is itself a solid target.
The marathon runner data comes from recreational runners with an average age in the low-to-mid 40s, a specific and fairly fit population. It doesn't establish how well the formula performs in untrained adults, adolescents, older sedentary populations, or elite athletes, groups where the age-heart rate relationship could look entirely different.
So what does that flashing number on a workout mean
Put together, the two studies here don't say the 220-minus-age formula is meaningless, the underlying trend of declining max heart rate with age was real in the runner sample. What they complicate is the idea that the formula's output is a precise personal number rather than a rough population average, one with a margin of error that seems to run in different directions for different people. A number that's off by several beats in one direction for one sex and the opposite direction for another isn't a small rounding error. It's a sign the formula is describing a group, not an individual.
A wrist sensor reading heart rate correctly in the first place is its own separate validation question, worth keeping apart from this one.
Common questions
Is the 220 minus age formula wrong?
Research testing it directly against measured maximal heart rate in recreational marathon runners found it didn't match precisely, with measured values running lower than predicted in women and higher than predicted in men. The formula reflects a general age-related trend rather than a precise individual figure.
Is Tanaka's formula more accurate than Fox's 220 minus age formula?
In the marathon runner study, both formulas showed a significant difference from measured maximal heart rate, and the two formulas produced different predicted values from each other. Neither was shown to match measured values exactly in that sample.
Why do stress testing labs use 85% of the predicted max heart rate?
Some exercise stress testing settings use that threshold as an endpoint, but a review of the practice questions its accuracy and notes that other measurements taken during testing, along with the significance of not reaching that threshold, may carry additional diagnostic information. Questions about what a specific test result means are a conversation for the clinician administering it.
Does age-predicted max heart rate work the same for men and women?
In the marathon runner study, the formula's error ran in opposite directions by sex, underestimating measured max heart rate in men and overestimating it in women, which suggests a single formula does not fit both groups equally.