Heart Rate Reserve Calculator

Heart rate reserve (HRR) is the gap between your maximum heart rate and your resting heart rate. It shows how much room your heart has to speed up during exercise. The Karvonen method uses that gap to set target heart rates, so the numbers fit your own resting heart rate.

What Heart Rate Reserve Measures

HRR is the number of beats per minute (bpm) between rest and your top effort. A person with a lower resting heart rate has a bigger reserve at the same age. HRR is not a fitness score and it does not diagnose anything. A normal resting heart rate for adults is 60 to 100 bpm when calm, and lower rates are common in athletes¹.

The Formula

HRR = HRmax - resting heart rate

Target heart rate = (HRR x intensity) + resting heart rate

The target heart rate method is named after Martti Karvonen, whose 1957 training study found that fitness gains began at around 60% of heart rate reserve². If you do not know your max heart rate, the calculator estimates it with one of three age formulas: Fox (220 - age), Tanaka (208 - 0.7 x age) or Gellish (207 - 0.7 x age)³ ⁴.

How This Calculator Computes Your Result

Enter your age and resting heart rate. Optionally, enter a max heart rate you measured in a hard test, or pick one of the three formulas. Tanaka is the default. If you enter a measured max, the formula is not used. The calculator rounds your max heart rate to a whole number, subtracts your resting heart rate to get HRR, then shows a target range in bpm for each intensity band. All values are in beats per minute.

What Your Result Means

Your result is your HRR in bpm plus a target heart rate range for each band. The bands below come from the American College of Sports Medicine (ACSM) and are based on percent of heart rate reserve⁵. The example column is for a 40-year-old with a resting heart rate of 60 bpm and a Tanaka max of 180 bpm (HRR of 120 bpm).

Moderate and vigorous bands are the ones ACSM recommends for most adults⁵.

Why Resting Heart Rate Changes Your Zones

A plain percent of max heart rate ignores resting heart rate. The Karvonen method does not. Take two 40-year-olds with the same max of 180 bpm. At 60% intensity, a person with a resting rate of 50 bpm gets a target of 128 bpm. A person with a resting rate of 80 bpm gets 140 bpm. The ACSM position stand notes that heart rate reserve methods may be preferable, because exercise intensity can be underestimated or overestimated when using percent of max heart rate alone⁵.

Percent of HRR is also not the same number as percent of max. For the 40-year-old above, 60% of HRR is 132 bpm, while 60% of max would be only 108 bpm. Do not compare a Karvonen target with a percent of max chart.

How Accurate Is the Max Heart Rate Estimate?

The formulas are averages, so they miss for individuals. The 220 minus age rule traces to a 1971 paper by Fox and colleagues, and Robergs and Landwehr found it was not derived from original research⁶. They reported an error of 7 to 11 bpm in max heart rate estimates⁶. Tanaka and colleagues built their formula from 351 studies covering 18,712 people, plus lab tests on 514 people. They found it held across sex and activity level, and that 220 minus age underestimates max heart rate in older adults³. Gellish and colleagues, tracking 132 people through 908 tests over 25 years, reached almost the same line⁴.

In a 2025 test of 230 adults who did a maximal treadmill test, all three formulas had an average error near 9 bpm (RMSE), and the range for most individuals was about plus or minus 18 to 24 bpm⁷. In plain terms, the standard deviation is around 10 bpm. Your real max could be 10 bpm higher or lower than the formula says, and sometimes more. If you want more precision, use a measured max from a supervised maximal test.