Health & Medicine · Fitness
Heart Rate Zone Calculator
Calculate your five personalized heart rate training zones based on your age and resting heart rate using the Karvonen heart rate reserve method.
Calculator
Formula
HR_target is the target heart rate in bpm, HR_max is the maximum heart rate (220 minus age), HR_rest is the resting heart rate in bpm, and intensity is the desired training zone percentage expressed as a decimal (e.g., 0.50 to 0.60 for Zone 1).
Source: Karvonen, M., Kentala, K., & Mustala, O. (1957). The effects of training on heart rate: A longitudinal study. Annales Medicinae Experimentalis et Biologiae Fenniae, 35(3), 307–315.
How it works
The Karvonen method begins by estimating your maximum heart rate (MHR) using the widely validated formula MHR = 220 − age. While this is a population-level estimate with a standard deviation of roughly ±10–12 bpm, it provides a reliable starting point for most healthy individuals. Athletes or older adults who know their true maximum heart rate from a graded exercise test (GXT) or field test can substitute that figure for greater accuracy.
The next step is calculating your Heart Rate Reserve (HRR), defined as the difference between your maximum and resting heart rate: HRR = MHR − HR_rest. Your resting heart rate should be measured first thing in the morning while still lying down for the most accurate reading. A lower resting heart rate generally indicates better cardiovascular fitness — elite endurance athletes often have resting heart rates below 40 bpm. The HRR reflects your functional cardiac output capacity and is the key variable that makes the Karvonen formula more personalized than simple percentage-of-max methods.
Each of the five training zones is then calculated by applying a lower and upper intensity percentage to the HRR and adding back the resting heart rate. Zone 1 (50–60% HRR) promotes active recovery and light aerobic conditioning. Zone 2 (60–70% HRR) is the foundational aerobic base zone, critical for endurance athletes. Zone 3 (70–80% HRR) improves aerobic efficiency and cardiovascular strength. Zone 4 (80–90% HRR) targets the lactate threshold — the intensity at which lactic acid begins to accumulate faster than it can be cleared. Zone 5 (90–100% HRR) represents maximal anaerobic effort, stimulating VO2 max adaptations and fast-twitch muscle fiber recruitment.
Worked example
Consider a 35-year-old individual with a resting heart rate of 62 bpm.
Step 1 — Maximum Heart Rate: MHR = 220 − 35 = 185 bpm
Step 2 — Heart Rate Reserve: HRR = 185 − 62 = 123 bpm
Step 3 — Zone Calculations (Karvonen formula applied):
- Zone 1 (50–60%): (123 × 0.50) + 62 = 123.5 ≈ 124 bpm | (123 × 0.60) + 62 = 135.8 ≈ 136 bpm
- Zone 2 (60–70%): 136 bpm – 148 bpm
- Zone 3 (70–80%): 148 bpm – 160 bpm
- Zone 4 (80–90%): 160 bpm – 173 bpm
- Zone 5 (90–100%): 173 bpm – 185 bpm
This individual should target Zone 2 (136–148 bpm) for the majority of their endurance training runs, and incorporate Zone 4 intervals (160–173 bpm) one to two times per week to raise their lactate threshold. Zone 5 efforts above 173 bpm should be used sparingly in structured high-intensity interval training (HIIT) sessions.
Limitations & notes
The formula MHR = 220 − age carries a standard deviation of approximately ±10–12 bpm, meaning the true maximum heart rate of any given individual can differ significantly from the estimate. Factors such as genetics, cardiovascular medications (particularly beta-blockers), altitude, heat, dehydration, and emotional stress can all shift heart rate responses independently of exercise intensity. The Karvonen formula also assumes a linear relationship between heart rate and oxygen consumption, which may not hold at the extremes of exercise intensity or in individuals with cardiac conditions. For clinical or high-performance athletic applications, a laboratory-measured VO2 max test or a physician-supervised maximal exercise test is strongly recommended to establish true MHR and lactate threshold zones. Additionally, resting heart rate should be measured consistently over several mornings and averaged for the best result.
Frequently asked questions
What is the most accurate way to measure my resting heart rate?
Your resting heart rate should be measured immediately upon waking, before getting out of bed or consuming caffeine. Use a chest-strap heart rate monitor or manually count your pulse at your wrist or neck for 60 full seconds. Averaging readings taken on three to five consecutive mornings will give you the most reliable baseline figure to use in the Karvonen calculation.
Which training zone is best for burning fat?
Zone 2 (60–70% HRR) is commonly referred to as the 'fat-burning zone' because the body relies predominantly on fat oxidation as a fuel source at this intensity. However, it's important to note that total caloric expenditure — which increases with intensity — is often more relevant to body composition goals. Combining Zone 2 long sessions with higher-intensity Zone 4 intervals yields optimal results for most individuals.
How is the Karvonen formula different from simply using a percentage of max heart rate?
Simple percentage-of-MHR methods (e.g., targeting 70% of 185 bpm = 130 bpm) ignore your resting heart rate entirely, producing the same zone for a sedentary person and a trained athlete of the same age. The Karvonen formula uses Heart Rate Reserve — the range between resting and maximum — to scale zones relative to your individual fitness level, resulting in meaningfully different and more personalized targets.
How much time should I spend in each zone per week?
Most endurance training frameworks recommend the 80/20 rule: approximately 80% of training volume in Zones 1 and 2, and 20% in Zones 3 through 5. This polarized distribution maximizes aerobic adaptation while minimizing injury risk and accumulated fatigue. Beginners may spend even more time in Zone 1 and Zone 2 before introducing higher-intensity work.
Can I use these zones for all types of exercise, including cycling and swimming?
Heart rate zones are generally applicable across all continuous aerobic activities, but there are modality-specific considerations. Swimming typically produces lower heart rates than running at the same perceived effort due to the horizontal body position and water cooling effect, and cycling produces slightly lower rates than running due to reduced muscle mass involvement. Some athletes establish separate zone sets for each sport using modality-specific max heart rate tests.
Last updated: 2025-01-15 · Formula verified against primary sources.