The formula
How to calculate heart rate zones
Zone 2 is the low-intensity aerobic zone that forms the bulk of most endurance training plans — easy enough to hold a conversation, hard enough to build the aerobic base faster sessions depend on. This estimates it from age and resting heart rate using the Karvonen method.
The 220 − age rule used here is the older, rougher estimate of maximum heart rate — it was never derived from a formal study, just fitted to scattered 1970s data, and individual variation runs around 10-12 bpm either way. A 30-year-old's estimated 190 bpm max could genuinely be anywhere from about 178 to 202 in reality.
What to enter:
- Age (years)
- Resting heart rate (bpm) — measured on waking, before getting out of bed, for the most accurate figure
Everything recalculates as you type, and the numbers in the address bar update with it, so a link to this page carries your figures with it.
None of the fields above need specialist equipment to fill in — the inputs are the kind of measurements that can be taken at home with a tape measure or scale, which is exactly why this style of calculation is widely used as a first, approximate check rather than a diagnostic one.
Why heart rate zones matters
People usually look up a heart rate zones calculation to put a number on something they can already sense but cannot quite quantify — how their fitness compares with a reference range, how a measurement is trending, or what a change actually means. A calculator turns that vague sense into a concrete figure, which is useful even though the figure itself is only ever an estimate.
It is most useful tracked over time rather than read once — a single reading tells you where you are today, while the same calculation repeated weeks or months apart, using the same method each time, shows the direction things are actually moving in.
It is also worth being honest about what a formula like this is actually built from. Most of the equations behind calculators like this one were derived from population studies — averages taken across large groups of people — and applied here as a general-purpose estimate rather than a measurement tailored to any one individual. That is a reasonable trade-off for a quick, free estimate, and it is also exactly why a result that looks unusual is worth discussing with a professional rather than acted on alone.
Where a result depends on more than one measurement, small errors in each input tend to compound rather than cancel out — a slightly mismeasured waist and a slightly mismeasured height, taken together, can shift a derived figure more than either error would on its own. Taking each measurement carefully, and ideally twice, is worth the extra minute it takes.
Worked example
Take the figures the calculator starts with:
- Age: 30 years
- Resting heart rate: 60 bpm
That gives:
- Estimated maximum heart rate: 190 bpm
- Heart rate reserve: 0 bpm
- Zone 2, low end: 0 bpm
- Zone 2, high end: 0 bpm
Those starting figures exist only to show the calculation working, not as a target or a reference value to compare yourself against — replace them with your own measurements in the calculator above and the same formula applies exactly as shown.
Reading the result
Commonly cited training guidance suggests 70-80% of weekly volume should sit in this zone rather than harder ones. Drifting above the high end on a session meant to feel easy is the most common sign of running it too hard.
Where this goes wrong. Because this uses the 220 − age formula rather than a measured maximum, the zone can be off by 10+ bpm for anyone whose real max is unusual for their age — if you know your actual max heart rate from a supervised test, use it directly instead. This is general fitness information, not medical advice; check with a doctor before starting new high-intensity training.
As with any general-purpose formula, the result here is an estimate derived from population averages, not a measurement specific to you — a reasonable starting point for a conversation with a qualified professional, not a replacement for one. Nothing on this page is medical advice.
Zone 2 is low-intensity aerobic exercise, roughly 60-70% of heart rate reserve, where the body relies heavily on fat for fuel. Its popularity follows research showing elite endurance athletes spend 70-80% of training time at this intensity.
The talk test is a simple check — you should be able to hold a full conversation without gasping. If you can only manage short phrases, you have drifted into Zone 3.
The headline figure is estimated maximum heart rate. With 30 years age and 60 bpm resting heart rate, that comes to 190 bpm. Change any field and the figure moves with it.
It uses a published formula applied exactly as defined, so the arithmetic itself is precise — but the formula is a population-level estimate, and individual results can vary from it for reasons the formula has no way to account for. Treat the output as a reasonable estimate rather than a measured or diagnostic value.
For most people, yes — a single reading is a snapshot, while the same measurement repeated consistently over weeks or months shows a trend, which is generally more informative than any one figure taken in isolation.
Small differences between calculators usually come down to which published formula or reference dataset each one uses — several equations in this area exist in more than one accepted version. This page states the specific formula used in the section above, so it is possible to check directly whether another source is using the same one.