Custom Heart Rate Zones: Why 220 Minus Age Misleads You
Asier G. Morato
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KEY TAKEAWAY
The 220 minus age formula was never derived from original research and carries a standard deviation of 10 to 12 beats per minute, enough to place you a full training zone away from your real physiology. Anchoring zones to a measured maximum heart rate, a lactate threshold, or cycling FTP fixes every metric built on top of them. FitWoody added custom heart rate and cycling FTP zones in version 2.6.
Custom heart rate zones are zones anchored to something measured on your own body: a real maximum heart rate from a hard effort, a lactate threshold, or for cycling a functional threshold power. Almost nobody starts there. Most of us start with 220 minus age, and that formula carries a standard deviation of 10 to 12 beats per minute (Robergs and Landwehr, Journal of Exercise Physiology Online, 2002). Zones are usually about 10% of your maximum wide, roughly 18 beats for a maximum of 185. So a two standard deviation miss, which is entirely ordinary in a group of any size, puts you a full zone off.
That matters more than it sounds. Every downstream number you care about (easy versus hard, time in zone 2, how much a session cost you, whether today counts as recovery) is calculated from those boundary lines. Get the lines wrong and the whole readout is wrong in a consistent direction, which is worse than random noise because it never looks obviously broken.
Where did 220 minus age actually come from?
Not from a study. Robergs and Landwehr traced it back to a 1971 paper by Fox, Naughton and Haskell, who plotted data points from around eleven previously published sources and drew a line through them. It was a rule of thumb for a clinical context, and it escaped into the world as a law. Their review concluded the equation has no scientific merit for use in exercise physiology, which is an unusually direct thing for a journal paper to say.
The better known replacement comes from Tanaka, Monahan and Seals (Journal of the American College of Cardiology, 2001), a meta-analysis of 351 studies covering 18,712 people. They proposed 208 minus 0.7 times your age, and showed that the old formula systematically overestimates maximum heart rate in young adults and underestimates it in older ones. Tanaka is a better average. It is still an average, with a similar individual spread around it.
How far off can a formula put your zones?
Run the arithmetic on yourself. At 40, both formulas agree: 220 minus 40 is 180, and 208 minus 28 is also 180. That agreement looks reassuring until you remember the spread. Roughly a third of people sit more than one standard deviation from a predicted value, so a real maximum of 168 or 192 at that age is unremarkable, not exotic.
Take the person whose real maximum is 192 but who trains off 180. Their zone 2 ceiling gets drawn near 126 when it belongs closer to 134. Their easy sessions are genuinely easy, maybe too easy, and their tempo work lands where threshold work should be. The person on the other side of the distribution has the opposite problem: they push into what the screen calls zone 2 while their body is in zone 3, which is the most common way an aerobic base plan quietly becomes a fatigue plan. If you want the physiology behind that, we wrote about what zone 2 training actually does.
Set your own zones in FitWoody
FitWoody reads your sleep, recovery and training load from your Apple Watch and tells you what each workout actually cost your body. Since version 2.6 you can set your own heart rate and cycling FTP zones, so every session is scored against your physiology instead of a formula from 1971. Free on the App Store, with a 7-day free trial of Plus.
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What should you anchor your zones to instead?
Three anchors, in rough order of how easy they are to get.
A measured maximum heart rate
The highest number your watch has genuinely recorded during a hard sustained effort, not a spike from a signal dropout on a cold morning. A field test gets most people close: a long uphill, or a set of hard repeats after a full warm up. It is unpleasant by design. If you have any cardiac risk factors, or any symptoms at all during exercise, that is a conversation for your doctor before it is a conversation for an app.
Lactate threshold
Threshold based zones anchor to the point where lactate starts accumulating faster than you can clear it. Coaches including Joe Friel, whose zone guide on TrainingPeaks is one of the most widely used references in endurance sport, build zones from lactate threshold heart rate rather than from maximum, because threshold moves as you train while maximum barely moves at all. You can estimate it from a 30 minute time trial, or measure it properly in a lab.
Functional threshold power, if you ride
On a bike, power is the cleanest anchor available. FTP is approximately the power you can hold for an hour, and unlike heart rate it does not drift with heat, caffeine, sleep debt or what you ate two hours ago. Heart rate tells you what a session cost you. Power tells you what you actually did. Both are worth having, which is why a good cycling setup keeps both sets of zones rather than picking a side.
What changes when the zones are actually yours?
Zone boundaries are not decoration on a chart. They feed time in zone, training load, workout scoring, and whether a day gets counted as recovery. Move the lines and every one of those numbers moves with them. This is the part people underestimate: setting zones is not a display preference, it is the definition of the units everything else is measured in.
It also changes the comparison you are making. Zones from a formula invite you to measure yourself against a population average. Zones from your own data let you measure yourself against yourself, which is the only comparison that leads anywhere useful. We have made the same argument about resting heart rate and HRV: your own baseline beats the normal range.
And it changes what cost means. The same 45 minutes at 150 bpm is a light aerobic session for one person and a threshold grind for another. Once the boundaries are right, what a workout actually cost you stops being a guess dressed up as a number.
How do you set custom heart rate zones in FitWoody?
FitWoody is an iOS app for iPhone, iPad and Apple Watch that turns the data your watch collects into a clear read on how your body is actually doing. In version 2.6, shipped in July 2026, we added custom zones: you set your own heart rate zones and your own cycling FTP zones instead of accepting a default. From that point on, your boundaries are the ones the app works from.
That was the point of building it. FitWoody already analyses workouts against your individual cardiac load rather than a generic template, and custom zones close the last place where a population formula was still doing the talking. It takes a couple of minutes to set, once.
What if you never do a maximum effort test?
Then use the best anchor you have and improve it later. Start from the highest heart rate your watch has genuinely recorded in the past year. Sanity check the zones it produces against how they feel: zone 2 should let you hold a conversation in full sentences, zone 4 should not. Adjust by a few beats when reality and the label disagree. Zones set from a real effort and refined by feel will beat a formula every time, and nobody needs to get this perfect on day one. Roughly right, then adjusted as you learn, is how almost everyone gets there.
Frequently asked questions
Is 220 minus age ever good enough?
As a first guess when you have no data at all, yes. As the foundation of a training plan, no. The 220 minus age formula was never derived from original research (Robergs and Landwehr, 2002) and carries a standard deviation of 10 to 12 beats per minute, so a large minority of people end up close to a full training zone away from where it places them. Use it for a week, then replace it with something you measured.
Do I need a lab test to set custom heart rate zones?
No. A lab lactate test is the most precise option, but a hard field effort after a proper warm up, or a 30 minute time trial used to estimate threshold heart rate, gets most people close enough to train off confidently. Nearly all of the accuracy gain comes from moving off an age formula onto your own measured number, not from lab grade precision.
How often should I update my heart rate zones?
Threshold based zones shift as fitness changes, so review them every few months or after a training block that clearly moved things. Maximum heart rate declines slowly with age and rarely needs adjusting more than once a year. The practical cue is feel: if easy sessions start feeling harder or easier than the zone label suggests, it is time to recheck the boundaries.