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Tool No. 05

HR Zone
Calculator

Enter your max and resting heart rate to calculate your five personalized training zones using the more accurate Karvonen (Heart Rate Reserve) method. Stop guessing whether you’re training easy or hard.

Your Heart Rate Data
bpm max
Best found via a hard field test — 220 minus age is a rough estimate only. A maximal 1-mile effort or the last 400m of a 5K gives a more accurate number.
bpm rest
Measure first thing in the morning before getting out of bed. Average over 3 days for best accuracy.
Heart Rate Reserve accounts for your resting HR, producing more personalized zones — especially accurate for well-trained runners with a low resting HR.
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Enter your heart rate data
to calculate your zones

Your 5 Training Zones
How It Works
The Karvonen Method,
Explained

Most generic HR zone calculators just multiply your max heart rate by a percentage. A runner with a resting HR of 40 and one with a resting HR of 70 get identical zones — which is wrong. The Karvonen method fixes this by using your Heart Rate Reserve (HRR): the difference between your max and resting HR.

The formula is: Target BPM = Resting HR + (Intensity% × HRR). A well-trained runner with a low resting HR gets zones that are meaningfully higher than a beginner at the same max HR — because they've built a bigger cardiovascular engine.

For the most accurate max HR, skip the 220-minus-age formula. Run a hard mile all-out or note your highest recorded HR in a recent 5K. That number is more reliable than any estimate.

Common Questions

What heart rate zone should most of my running be in?

Zone 2 — aerobic base. Most serious runners should be doing 70–80% of their weekly mileage here. It feels almost embarrassingly easy. That's the point. Zone 2 builds the fat-burning aerobic engine that makes every other zone more sustainable.

What zone is a half marathon run at?

For most trained runners, a half marathon sits in Zone 4 — threshold effort. Elite runners may dip into high Zone 3. If you're spending significant time in Zone 5 during a half, you went out too fast.

Why is my heart rate so high on easy runs?

This is one of the most common issues for newer runners. Your cardiovascular system hasn't adapted yet to deliver oxygen efficiently at lower intensities. The fix is consistent easy running over months — not weeks. Slow down more than feels necessary. It works.

How do I find my true max heart rate?

The most reliable field test: after a proper warm-up, run a hard 800m or 1 mile at max effort. Your peak HR reading near the end of that effort is close to your true max. Do this on a flat surface and check the peak number on your watch afterward — not during.

Karvonen vs percentage of max — which should I use?

Karvonen for anyone with a resting HR below 55 or above 65 — those are the runners where the difference matters most. Percentage of max is fine as a starting point if you don't know your resting HR, but it systematically undercalculates zones for fit runners and overcalculates them for beginners.
Field Note
One Watch Metric That Actually Matters — why running power beats pace and HR in the moments that count.
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