The formula
How to calculate target heart rate
Target heart rate zones translate training intensity into a number you can see on a watch. The three shown here cover the range most endurance plans are built around: easy aerobic work, steady aerobic work, and threshold effort.
The zones use heart rate reserve rather than a flat percentage of maximum, which accounts for your resting rate and produces figures that suit your current fitness.
What to enter:
- Age (years)
- Resting heart rate (bpm)
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 target heart rate matters
This kind of calculation gets used both out of general interest and ahead of a specific conversation — with a trainer, a midwife or a GP — where having an actual number ready, rather than a description, makes that conversation more concrete and specific.
Because the calculation depends on a formula rather than a device, it is useful anywhere a scale, a tape measure or a stopwatch is available, without needing specialist equipment — which is also exactly why it should be treated as an estimate rather than a clinical measurement.
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: 38 years
- Resting heart rate: 60 bpm
That gives:
- Easy, 60% of reserve: 133 bpm
- Aerobic, 70% of reserve: 145 bpm
- Threshold, 85% of reserve: 163 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
Most endurance training should sit at or below the easy figure — roughly 80% of sessions in a well-structured week. The common mistake is spending most of the week between the aerobic and threshold numbers, which is hard enough to tire you and not hard enough to drive adaptation.
Where this goes wrong. Heart rate lags effort by a minute or two and drifts upward during long sessions in heat. For short intervals, pace or power is a better guide than heart rate, which simply cannot respond fast enough.
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.
Around 60–70% of heart rate reserve, where fat supplies the largest share of energy. Higher intensities burn more fat in absolute terms per minute despite using a smaller proportion, so for weight loss total calories matter more than the zone.
The talk test is a reasonable check. Easy means full sentences comfortably; aerobic means short sentences; threshold means a few words at a time.
It returns easy, 60% of reserve. With 38 years age and 60 bpm resting heart rate, that comes to 133 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.