Heart rate zone calculator

Enter your age (or a known max heart rate), your resting heart rate and, if you have one, your lactate threshold heart rate. The calculator shows Zone 1–5 in beats per minute under three common methods: percent of max heart rate, heart-rate reserve (Karvonen) and lactate threshold heart rate (Friel). These are the same formulas the Just Zones app uses.

Age Estimates max HR

Max HR (optional) Replaces the age estimate

Resting HR Used by Karvonen

LTHR (optional) Used by the LTHR method

Ranges are in bpm. Each zone runs from its lower bound up to one beat below the next zone's lower bound, and Zone 5 has no upper limit. A heart rate below Zone 1 falls outside every zone.

Track time in these zones from your Apple Watch

Just Zones applies these same zones to the heart-rate data from your Apple Watch workouts in Apple Health and shows how many minutes of each workout and each week you spent in every zone. Resting heart rate can come straight from Apple Health; age, max HR and LTHR are typed in, and you can set any zone's bound by hand.

How the calculator works

Max heart rate. When you enter a max HR, the calculator uses it as is. Otherwise it estimates max HR from age with the Tanaka formula:

% of max HR. Each zone's lower bound is a percentage of max HR: 50% for Zone 1, then 60, 70, 80 and 90%. This is the only method that needs no resting heart rate.

Karvonen (heart-rate reserve). Heart-rate reserve is max HR minus resting HR. Each zone starts at a percentage of that reserve added on top of resting HR, with the same 50/60/70/80/90% split.

LTHR (Friel). Zones are percentages of lactate threshold heart rate, following Joe Friel's run zones: Zone 2 starts at 85% of LTHR, Zone 3 at 90%, Zone 4 at 95% and Zone 5 at 100%. Friel leaves Zone 1 as "below Zone 2"; Just Zones uses 65% of LTHR as the Zone 1 floor.

Bounds are rounded to the nearest whole beat. The same heart rate can land in different zones under different methods, which is why each result above names its method. More detail and a worked example: how heart rate zones are calculated.