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)
Results appear immediately — there is nothing to submit. Changing a field rewrites the link, so you can share the exact scenario you are looking at.
If an exact figure for one of the fields is not available, a careful estimate is a reasonable starting point, since the calculator recomputes instantly the moment a more accurate number is available — nothing here depends on getting every field exact on the first pass.
Why target heart rate matters
People usually look up a target heart rate 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.
This tends to get checked before or after a change in routine — a new training block, a change in diet, a different stage of a pregnancy — as a way of putting a figure on something that would otherwise only be felt rather than measured.
A single number like this is most useful placed in context rather than read in isolation. Reference ranges exist because bodies vary considerably and still count as healthy across a wide spread of values, so a result sitting outside a commonly quoted range is a prompt to look more closely rather than a verdict on its own. The same figure, tracked consistently over time, tends to say more than any single reading ever will.
In practice, this kind of figure is often calculated more than once with slightly different inputs to see how sensitive it is — trying a measurement taken this morning against one taken yesterday evening, for instance, to see how much normal daily variation actually moves the result. That habit is a good one: it builds a feel for how much a single reading can be trusted on its own before drawing any conclusion from it.
Worked example
Work through the defaults on this page:
- 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.