Heart Rate Reserve Calculator
Heart rate reserve (HRR) is the range of heart rates available during exercise, calculated as your maximum heart rate minus your resting heart rate. The Karvonen formula uses HRR to set training zone targets that account for individual resting heart rate, making zones more accurate than simple percentage-of-maximum methods. Enter your maximum heart rate (measured or estimated from 220 minus age) and your resting heart rate to calculate your HRR and Karvonen-based training zones from 50 to 90 percent intensity.
Heart rate reserve and Karvonen formulas
HRR = HRmax - HRresting
Target HR = HRresting + (intensity × HRR)
For example, a 70 percent intensity target for an athlete with HRmax = 190 and HRresting = 60: HRR = 190 - 60 = 130. Target HR = 60 + (0.70 x 130) = 60 + 91 = 151 bpm. The Karvonen method was described by Martti Karvonen and colleagues in 1957 and is widely referenced in exercise prescription guidelines.
Using heart rate zones in training
- 50 to 60 percent: Very light recovery. Improves overall health, good for warm-up and cool-down.
- 60 to 70 percent: Light aerobic. Fat burning zone, builds base endurance.
- 70 to 80 percent: Moderate aerobic. Improves cardiovascular efficiency and aerobic capacity.
- 80 to 90 percent: Hard aerobic to threshold. Develops lactate threshold and race pace fitness.
- 90 percent and above: Very hard, anaerobic. Short intervals only, requires longer recovery.
Heart rate reserve calculator: frequently asked questions
What is heart rate reserve?
Heart rate reserve (HRR) is the difference between your maximum heart rate and your resting heart rate: HRR = HRmax - HRresting. It represents the range of heart rates available for exercise. A higher HRR generally indicates better cardiovascular fitness.
How do I find my maximum heart rate?
The most common age-predicted estimate is HRmax = 220 - age. More accurate but effort-intensive methods include a graded exercise test to exhaustion or a field test sprint. The 220 minus age formula has a standard deviation of about 10 to 12 beats per minute, so individual variation can be significant.
What is the Karvonen formula for training zones?
The Karvonen method calculates target heart rate as: THR = HRresting + (intensity fraction x HRR). For example, 70 percent intensity = HRresting + (0.70 x HRR). This method accounts for resting heart rate, making zone targets more personalized than zones based purely on percentage of maximum heart rate.
Why does the Karvonen method give different zones than percentage of HRmax?
Because it incorporates resting heart rate. Two athletes with the same HRmax but different resting heart rates (say, 50 versus 70 bpm) will have different HRRs, and therefore different target zones at the same percentage. The Karvonen method is generally considered more accurate for individual prescription.
What is a normal resting heart rate?
For adults, a normal resting heart rate is between 60 and 100 beats per minute. Well-trained endurance athletes often have resting heart rates of 40 to 55 bpm. Resting heart rate should be measured first thing in the morning before getting out of bed for the most accurate reading.
Official sources
- Karvonen, M.J., Kentala, E., & Mustala, O. (1957). The effects of training on heart rate. Annales Medicinae Experimentalis et Biologiae Fenniae, 35(3), 307-315.
- American College of Sports Medicine (ACSM) Guidelines for Exercise Testing and Prescription: acsm.org.
- Centers for Disease Control and Prevention: Target Heart Rate and Estimated Maximum Heart Rate.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.