How this instrument works
This calculator returns a training range, not a single number: pick a low and high intensity percentage, and it applies the Karvonen heart-rate-reserve formula to both ends to produce a floor and ceiling in beats per minute. That range format is what makes it suited to structured zone training, where the goal is staying inside a band for the duration of a session rather than hitting one exact target pulse.
The Karvonen method itself, published by Finnish researcher M.J. Karvonen and colleagues in 1957, calculates heart rate reserve as the gap between maximum and resting pulse, then adds a percentage of that reserve back onto the resting rate. That construction means two people who share an identical maximum heart rate but differ in fitness — and therefore in resting pulse — get different zone boundaries for the same intensity percentage, which a flat percentage-of-maximum method can't distinguish.
Common zone bands used in coaching, loosely: 50-60% for easy recovery days, 60-70% for aerobic base-building, 70-85% for tempo or threshold efforts, and 85% and above for short, hard intervals. These aren't fixed physiological boundaries so much as widely used coaching conventions — treat them as a starting framework to adjust against how sessions actually feel and how well you recover from them.
- Enter Maximum heart rate — from a measured max-effort test, a wearable's recorded peak, or an estimate from this site's max-heart-rate calculator.
- Enter Resting heart rate — ideally measured first thing in the morning before getting out of bed.
- Set Target intensity, low end and high end — the percentage band you want to train within, for example 60 to 70 for an aerobic-base session.
- Read Target heart rate, low end and high end — the beats-per-minute range to stay inside during the session.
- Low-end intensity must be at or below high-end intensity, and max heart rate must exceed resting heart rate, or the instrument will flag the inputs.
Worked example — max 185, resting 60, a 60-70% zone
Enter a maximum heart rate of 185 bpm, a resting heart rate of 60 bpm, and a 60-70% intensity band. Heart rate reserve is 185 - 60 = 125 bpm. The low end of the zone is (125 x 0.60) + 60 = 135 bpm, and the high end is (125 x 0.70) + 60 = 147.5 bpm, so the target zone for this session is 135 to 147.5 bpm.
Widen the band to 50-85% instead, with a max of 170 and a resting pulse of 70, and the range stretches much further: reserve is 170 - 70 = 100 bpm, giving a low end of (100 x 0.50) + 70 = 120 bpm and a high end of (100 x 0.85) + 70 = 155 bpm — a 35-beat-wide zone appropriate for a session mixing easy and hard efforts rather than one steady intensity.
Questions
What's the advantage of a range over a single target heart rate?
A range gives real-time flexibility during a session — you can drift between the floor and ceiling as terrain, fatigue or pacing change, without constantly chasing one exact number. It also matches how most structured training plans are actually written, describing sessions as 'stay in zone 2' rather than 'hold exactly this one pulse,' which is easier to sustain in practice.
How do the common training zone bands map to training goals?
As a rough coaching convention: 50-60% intensity suits easy recovery days, 60-70% builds aerobic base at a comfortable, sustainable pace, 70-85% covers tempo and threshold work, and 85% or above is reserved for short, hard interval efforts. These bands are common practice rather than fixed physiological cutoffs, so adjust them against how your own sessions feel and recover.
Where do I get accurate numbers for max and resting heart rate?
Maximum heart rate ideally comes from a supervised max-effort test or a genuinely hard race/interval effort recorded on a chest strap; this site's max-heart-rate calculator offers an age-based estimate if you don't have a measured number. Resting heart rate is easiest to get accurately first thing in the morning, before sitting up, over a few consecutive days to average out day-to-day noise.
Is this the same calculation as the site's Karvonen Formula calculator?
Yes, identical underlying math. The Karvonen Formula calculator, in this site's health section, goes deep on the formula's 1957 origin and compares it against the common 220-minus-age heart-rate estimate. This page applies the same formula but is built specifically around a low-to-high training-zone range rather than a single number, for structured zone-based training.
How is this different from the target-heart-rate calculator?
Same Karvonen reserve formula, different output shape. The target-heart-rate calculator returns one single beats-per-minute number for a single intensity percentage, useful when you just want one number to aim for during a session. This calculator instead takes a low and a high percentage and returns a full range, better suited to zone training where staying inside a band matters more than hitting one exact figure.