How the calculation works
First the calculator estimates your maximum heart rate from your age, or takes the value you entered. Then it splits it into five zones of 10 percentage points each, starting at 50%.
Maximum heart rate = 208 − 0.7 × age (Tanaka), or 220 − age (Fox)
Zone, share of maximum = maximum × share
Zone, heart rate reserve = resting + (maximum − resting) × share
Values are rounded to whole beats per minute. The upper limit of one zone is the lower limit of the next.Worked example
Age 50, Tanaka formula, share of maximum.
- Maximum heart rate: 208 − 0.7 × 50 = 173 beats per minute.
- Zone 1 (50 to 60%): 86.5 to 103.8, shown as 87 to 104.
- Zone 3 (70 to 80%): 121.1 to 138.4, shown as 121 to 138.
- Zone 5 (90 to 100%): 155.7 to 173, shown as 156 to 173.
With a resting heart rate of 60 and the reserve method, zone 3 becomes 60 + (173 − 60) × 0.70 = 139.1 to 60 + (173 − 60) × 0.80 = 150.4, shown as 139 to 150.
What this calculator does not include
- Your real maximum heart rate, which differs from the formula by 10 beats a minute or more for many people.
- Fitness level, heat, sleep, caffeine, illness and medicine, which all change your heart rate.
- Medical conditions. This is not a substitute for a stress test or advice from a doctor.
Results are estimates for information, not medical advice. Last updated: 12 November 2026.
Frequently asked questions
What are heart rate zones?
Heart rate zones split your effort into ranges of beats per minute. Low zones feel easy and build basic endurance, higher zones feel hard and train speed and power. Many training plans use five zones.
How is my maximum heart rate estimated?
The calculator uses the Tanaka formula, 208 minus 0.7 times your age, by default. You can also use the older formula, 220 minus your age, or enter a maximum you measured yourself. Both formulas are averages.
What is the difference between the two zone methods?
The simple method takes shares of your maximum heart rate. The heart rate reserve method, also called Karvonen, takes shares of the gap between your maximum and your resting heart rate and adds your resting heart rate. It needs your resting heart rate, and it suits people with a very low or high resting heart rate better.
How do I measure my resting heart rate?
Check your pulse for a full minute when you wake up, before getting out of bed, on a few mornings, and take the average.
Is this suitable for everyone?
No. It is for healthy adults aged 18 and over. If you have a heart condition or take medicine that changes your heart rate, such as beta blockers, ask a doctor how to train. The formulas also miss by 10 beats a minute or more for many people, so use how you feel as a second check.