Garmin heart rate zones calculator
Garmin Connect can build your five zones from three different bases, and they produce genuinely different numbers. This works out all three so you can see what your watch is using and whether it's the right one.
The three bases, and which one to use
Percentage of maximum heart rate
Garmin's default, and the one you're almost certainly on. Your range is split 50-60-70-80-90-100, straight percentages of whatever maximum sits in your user profile. Simple, and only as good as that maximum.
The catch: unless you've corrected it, Garmin filled that field with an age estimate. Every zone you've trained in since is built on a guess.
Percentage of heart rate reserve
Reserve is your maximum minus your resting heart rate, the span you actually have to work with. Zones are the same percentages applied to that span and then added back to your resting rate, which is the Karvonen method.
This is the better choice if you know both numbers. It accounts for the fact that a fit person with a resting rate of 45 and an unfit person at 70 are doing different amounts of work at the same percentage of max. Expect the numbers to come out higher than the percentage-of-max version.
Percentage of lactate threshold
The most useful basis if your watch has detected a threshold, because it's anchored to a real physiological event rather than an estimate. Garmin splits it tightly: everything under 85% is zone 1, and zone 5 starts at your threshold itself.
Compatible Garmin watches detect lactate threshold automatically during a hard run with a chest strap, or you can run a guided test. If you have the number, use it.
Where to change this on your watch
In Garmin Connect, open the menu, then User Settings, then Heart Rate Zones. You can set the basis there, edit the maximum, and choose whether zones apply to all activities or differ per sport. Running, cycling and swimming can each carry their own set, which is worth doing: your cycling maximum typically runs about 5 to 10 beats below your running maximum.
If you change your max heart rate, previous activities keep the zone breakdown they were recorded with. Only new activities use the new zones.
Getting a real maximum heart rate
An age formula is a population average with a standard deviation of 10 to 12 beats, so yours could sit well either side. Two ways to do better.
- Look at your own data. The highest heart rate Garmin has ever recorded for you during a hard effort is usually closer to the truth than any formula, as long as it isn't a strap glitch. A single spike 30 beats above everything else is an artefact, not a maximum.
- Run a test. After a thorough warm-up, three hard hill repeats of about three minutes, going all out on the last one. The highest number you see is close to your maximum. Don't do this without a decent training base.
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Ask your watch instead of estimating.
Connect Garmin to Claude or ChatGPT and ask for your real maximum, your detected threshold, and how your time in each zone has actually broken down over the last month.