Heart rate zone calculator
Your five heart rate zones from the best data you have: heart rate reserve, threshold HR or max HR, using the Tanaka formula.
Updated 16 September 2026
Heart rate zones work across all four endurance sports: they are the only marker still valid when pace stops meaning anything — uphill, in the water, in heat, or on the bike.
Provided they are built on the right anchor. Three methods exist and they are not equivalent: the best data you have determines which one to use.
Average HR over an all-out 30 to 60 minute race
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How it is computed
If you know your threshold heart rate (average HR over an all-out 30 to 60 minute race), that is the best anchor: zones are set as a percentage of it. It is the most reliable method, because threshold moves with training while max HR does not.
If you know your max HR and resting HR, the Karvonen formula uses heart rate reserve — the difference between the two. It is more accurate than a plain percentage of max HR, especially for the low zones, because it accounts for your actual resting rate.
If age is all you have, we use Tanaka: 208 − 0.7 × age. Not “220 − age”, which comes from a 1971 eyeball fit never meant as a predictive formula and is off by 10 beats on a 50-year-old. Either way the standard deviation is around 7 beats: a measured max HR always beats an estimate.
The plans built from this number
Now the plan that goes with it
These numbers are exactly the ones Endu uses to build a full preparation: phases, volume, detailed sessions, exported to your watch. 14-day trial, cancel any time.
Create my planFrequently asked questions
- How do I actually measure my max HR?
- On a hill, after a full warm-up: 3 all-out 3-minute climbs with 2 minutes recovery, then read the highest value of the last one. An all-out 5 or 10 km race also gives a good approximation over the final kilometre. Avoid it if you have any cardiac doubt.
- Does my max HR drop with training?
- No — it declines with age, very slowly, and training barely changes it. What improves is your ability to hold a high percentage of it, and your resting rate coming down. That is why threshold-anchored zones are more useful to track.
- Why is my HR lower on the bike than running?
- It is normal: 5 to 10 beats lower for the same effort, because you are seated and less muscle mass is working. In swimming the gap is larger still, up to 15 beats, due to the horizontal position and immersion. A triathlete therefore has three sets of zones, not one.
- Should I train in zone 2 all the time?
- Around 80 % of the volume, yes. But cardiac “zone 2” is not the zone 2 social media talks about: it is simply easy endurance, the pace at which you can hold a conversation. The remaining 20 % must be genuinely hard, otherwise polarisation achieves nothing.