What this calculator does
Simple percentage-of-maximum training zones ignore resting heart rate, which means a fit person and an unfit one of the same age get the same target despite very different capacities. The Karvonen method fixes that by working from heart rate reserve.
Reserve is the gap between resting and maximum, and it is what training intensity should be a percentage of. A 35 year old with a resting rate of 65 has a reserve of 120 bpm, giving a 50 to 75 per cent zone of 125 to 155 bpm.
The formula
Maximum heart rate is estimated as 220 less age. Resting heart rate is subtracted to give the reserve, the intensity percentage is applied to that, and the resting rate is added back.
| Term | Meaning |
|---|---|
| Heart rate reserve | Maximum heart rate less resting heart rate: the range available for exercise. |
| Karvonen method | Applying intensity to the reserve rather than to maximum heart rate. |
| 220 minus age | The conventional maximum heart rate estimate, which carries a wide margin of error. |
The inputs explained
| Field | What to enter |
|---|---|
| Age (years) | Age in years, used for the maximum heart rate estimate. |
| Resting heart rate (bpm) | Resting heart rate in bpm, best measured on waking before getting up. |
| Lower intensity (%) | Lower intensity bound as a percentage of reserve. |
| Upper intensity (%) | Upper intensity bound as a percentage of reserve. |
When to use it
Setting training zones
The reserve method accounts for fitness in a way percentage-of-maximum does not.
Comparing two people of the same age
A lower resting rate produces a different zone for the same intensity.
Planning an endurance programme
Different sessions target different percentages of reserve.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How does age change the training zone?
The same resting rate at three ages.
| Age | Target heart rate zone | Heart rate reserve |
|---|---|---|
| 25 years | 130 - 163 bpm | 130 bpm |
| 35 years | 125 - 155 bpm | 120 bpm |
| 55 years | 115 - 140 bpm | 100 bpm |
Questions
Why use reserve rather than maximum heart rate?
Because the resting rate is the floor that exercise builds from, not zero. A fit person with a resting rate of 45 has far more reserve than someone at 75, and applying a percentage to maximum alone ignores that difference entirely.
How accurate is 220 minus age?
As a population average it is reasonable, but the standard deviation is roughly 10 to 12 bpm, so an individual can be well above or below it. A measured maximum from a supervised test is considerably more reliable.
How should resting heart rate be measured?
On waking, before getting out of bed, ideally averaged across several mornings. A reading taken during the day after coffee or activity will be too high and will shift the whole zone.
Should I train within these zones?
They are a general guide rather than a prescription. Anyone starting exercise after a period of inactivity, or with a heart condition or on medication affecting heart rate, should discuss training intensity with a doctor first.
For cardiac workload during exercise, see the rate pressure product calculator. For total daily energy needs, see the TDEE calculator.