Karvonen Formula Calculator

The Karvonen Formula calculates your target heart rate (THR) training zones using your Heart Rate Reserve (HRR), which is the difference between your maximum and resting heart rates. The formula is: THR = ((MHR − RHR) × Intensity%) + RHR. By factoring in your resting heart rate, it produces more personalized zones than simple percentage-of-max methods.

Measure your resting heart rate first thing in the morning before getting out of bed. Count your pulse for 60 full seconds, or count for 30 seconds and multiply by two. For best accuracy, take readings on 3–5 consecutive mornings and use the average — daily variation of 5–10 bpm is normal due to stress, sleep quality, and training load.

The 220 − age formula is a widely used estimate but has a standard deviation of roughly ±10–12 bpm, meaning your true max HR could differ significantly. A more accurate alternative is 206.9 − (0.67 × age). Athletes and serious exercisers should consider a supervised maximal effort test for the most precise result.

Heart Rate Reserve is simply your Maximum Heart Rate minus your Resting Heart Rate: HRR = MHR − RHR. For example, if your MHR is 190 bpm and your resting HR is 65 bpm, your HRR is 125 bpm. A higher HRR generally indicates better cardiovascular fitness.

For general health and endurance base-building, Zone 2 (light, 20–39% HRR) and Zone 3 (aerobic, 40–59% HRR) are most recommended. Many endurance coaches advocate spending up to 80% of training time in Zone 2 to build aerobic capacity while minimizing recovery demands. Higher zones are reserved for interval and race-pace work.

Basic calculations simply multiply your maximum heart rate by a percentage (e.g. 70% × 190 = 133 bpm). The Karvonen method incorporates your resting heart rate, which adjusts zones upward for fitter individuals who have lower resting HRs. This makes Karvonen zones more individualized and is why it's considered the gold standard by the ACSM.

The fat-burning zone typically corresponds to Zone 2, roughly 20–39% of your HRR using the Karvonen method (or about 50–65% of max HR). At this intensity, your body uses a higher proportion of fat as fuel. However, total calorie burn is lower than at higher intensities, so overall fat loss depends on total energy expenditure and diet.

Yes — heat, humidity, altitude, and fatigue can all elevate your heart rate at a given effort level. In hot or humid conditions, your heart rate may run 5–10 bpm higher than usual. In these cases, you may want to train by perceived effort (RPE) alongside your HR zones, or shift your target zones slightly upward to account for cardiac drift.