Karvonen Formula Calculator

The Karvonen Formula is a method for calculating target heart rate that accounts for your individual fitness level by using your heart rate reserve (HRR) — the difference between your maximum and resting heart rate. The formula is: THR = ((MHR − RHR) × Intensity) + RHR. This makes it more personalized than simple percentage-of-max-heart-rate methods.

Heart rate reserve (HRR) is simply your maximum heart rate minus your resting heart rate. For example, if your max HR is 190 bpm and your resting HR is 65 bpm, your HRR is 125 bpm. The Karvonen Formula uses this reserve to scale your target heart rate based on effort intensity.

The 220 − Age formula is a common estimate but can vary by ±10–20 bpm for individuals. It's a convenient starting point, especially if you haven't done a max effort test. For greater accuracy — particularly for serious athletes — a supervised maximum exercise test or a 3-minute all-out field test is recommended.

Measure your resting heart rate first thing in the morning before getting out of bed. Count your pulse for 60 seconds (or 30 seconds and double it). For best accuracy, take readings on 3–5 consecutive mornings and use the average, as stress, training load, and sleep can cause day-to-day variation of 5–10 bpm.

For general health and aerobic fitness, most experts recommend spending the majority of your training time in Zone 2 (moderate intensity, 40–59% HRR). This builds aerobic base, improves fat metabolism, and aids recovery. Higher zones (4–5) are reserved for interval training and should make up a smaller portion of weekly volume.

The fat-burning zone is generally considered to be around 50–70% of your heart rate reserve using the Karvonen Formula. At this intensity, your body relies more heavily on fat as a fuel source. However, total calorie burn and training consistency matter more for fat loss than staying exclusively in this zone.

Basic methods calculate target HR as a percentage of maximum heart rate only (THR = MHR × Intensity%). The Karvonen Formula applies the intensity percentage to your heart rate reserve and then adds back the resting heart rate. This means two people with the same max HR but different resting heart rates will get different training zones, making the Karvonen approach more individualized.

Yes. Heat and humidity increase cardiovascular strain, causing your heart rate to rise at any given effort level. At altitude, reduced oxygen availability also elevates heart rate. In these conditions, consider working at the lower end of your target zone or using perceived exertion alongside heart rate to avoid overtraining.