Last updated: 31 July 2026
Training zones tell you how hard a run was and how hard the next one should be. Most calculators derive them from your age. Runnerd computes them from your pulse — in two ways, with different precision. The calculator below runs the same maths as the app.
Without a usable resting heart rate Runnerd computes with % HRmax — which is what is happening here.
The maths runs in your browser. Your values never leave the page.
The defaults are 180 and 60. Those are the same values Runnerd computes with as long as it knows nothing better about you.
Karvonen does not compute from your maximum heart rate but from your heart rate reserve — the span between resting and maximum. That is the range your training actually happens in:
An example shows what that does. Take a maximum heart rate of 186. The boundary at 70 % then sits:
16 beats of difference for the same runner — purely because one method knows their resting heart rate and the other does not. In Runnerd, that 70 % boundary is exactly the line between easy and hard. So the choice of method helps decide how many of your runs count as easy.
The formula goes back to Martti Karvonen, 1957.
The rule of thumb comes from a regression across many people. As an average it holds up. For an individual it barely does: the scatter is around 10 beats, and considerably more for some.
A 40-year-old with a true maximum of 195 gets 180 out of the formula. Every zone then slides 15 beats down. In practice that means easy runs get too fast and hard runs too slow. Together, those two are the most reliable way to run a lot and stay slow.
This is why Runnerd derives your maximum heart rate from your runs, not from your year of birth.
Runnerd counts Z1 and Z2 together as easy — everything below 70 %. That is the basis for checking whether your ratio of easy to hard runs holds up.
Both methods use the same percentage bands. They differ only in what the percentage refers to.
% HRmax takes the maximum heart rate as a whole. It works without a resting rate and is enough for most runners. In Runnerd it is the default.
Karvonen takes the reserve. It gets more accurate the fitter you are — because a low resting heart rate is exactly what % HRmax overlooks.
If no usable resting rate exists, Runnerd falls back from Karvonen to % HRmax automatically. And anyone who knows their zones from a lab test enters all 5 by hand. Those boundaries then win over either method.
Three stages, in this order. A value you entered yourself always wins. Otherwise Runnerd takes the highest maximum across your runs of the past 12 months. If that sits below 140, Runnerd discards it as implausible and computes with 180.
That has a consequence worth knowing. If you have never truly run hard, your detected maximum is too low. Every zone then slides down with it. A real race over 5 or 10 km gives the most usable value.
Change your maximum heart rate or the method and Runnerd recomputes the zone distribution of every past run. Otherwise old and new runs would sit on different scales.
Heart rate arrives late. A 400 m rep is over before your pulse is up. By time-in-zone an interval session therefore looks tamer than it was. That is one reason Runnerd rates load with TRIMP rather than zone time alone.
Heart rate drifts. Same pace, higher pulse later in a long run. In heat, more so. The same effort then lands in a higher zone.
And the rest of life counts. Coffee, short sleep, altitude and an infection on its way shift your pulse as well.
Zones steer your effort. Judging it is beyond them.
The share the Karvonen formula uses is exactly the quantity Runnerd computes training load with: heart rate reserve. A run at 0.73 costs exponentially more than one at 0.63. How weeks of that turn into fitness, fatigue and form is on the page about CTL, ATL and TSB.
Download Runnerd and let it read your Apple Health data once. Your zones then sit in settings under heart rate zones, with your real values. The 180 and 60 from this calculator stop mattering. And every run shows how much time sat in which zone.
Runnerd is free. Pro unlocks the full analytical depth, a one-time 8.99 € for Mac and iPhone together. No subscription.
Get Runnerd on the App Store · The readiness score · What your Apple Health data holds
Runnerd is not a medical product and does not replace medical advice. If you have a pre-existing condition or have not trained for a long time, discuss your limits with a doctor first. Apple, Apple Health, Apple Watch, HealthKit and App Store are registered trademarks of Apple Inc.