Target Heart Rate Calculator

The Karvonen Formula Explained

The Karvonen formula calculates a target heart rate using heart rate reserve (HRR) — the gap between your estimated maximum heart rate and your resting heart rate — rather than a percentage of maximum heart rate alone:

$$\text{THR} = ((220 - \text{age} - \text{RHR}) \times \%\text{Intensity}) + \text{RHR}$$

Why Karvonen Is More Personalized Than the Simple Percentage Method

A simpler, older method calculates target heart rate as a straight percentage of estimated maximum heart rate: Target HR = (220 − age) × %Intensity. That formula treats two people of the same age identically, regardless of fitness level. Karvonen's heart rate reserve approach instead starts from (220 − age − RHR) — a fitness-adjusted range — before applying the intensity percentage and adding resting heart rate back in. Two 35-year-olds with resting heart rates of 55 and 75 bpm will get meaningfully different target zones from Karvonen, but the same target zone from the simple percentage method, even though the lower resting heart rate typically signals better cardiovascular conditioning and a different appropriate training zone.

Worked Example

For a 35-year-old with a resting heart rate of 65 bpm, training at 70% intensity: Heart Rate Reserve = 220 − 35 − 65 = 120. Target HR = (120 × 0.70) + 65 = 84 + 65 = 149 bpm. At the top of a 70-84% cardio zone (84% intensity): Target HR = (120 × 0.84) + 65 ≈ 166 bpm. So this person's cardio-zone target heart rate range is roughly 149 to 166 bpm.

Understanding Heart Rate Zones

Lower-intensity zones (roughly 50-69% of heart rate reserve) are commonly labeled "fat burn," since a higher proportion of calories burned at that intensity comes from fat stores, though total calorie burn per minute is lower than at higher intensities. Mid-range zones (70-84%) are typically labeled "cardio," building cardiovascular endurance while remaining sustainable for extended periods. The "peak" zone (85% and above) is high-intensity training, generally sustainable only in short intervals and typically reserved for well-conditioned individuals.

Common Target Heart Rate Mistakes

Using a stale or estimated resting heart rate rather than an actual morning measurement is a common source of error — resting heart rate can shift meaningfully as fitness improves, so a number from months ago may no longer reflect current fitness. Confusing heart rate reserve percentage with percentage of maximum heart rate is another — the two methods produce different numbers for the same stated "intensity," and mixing them up can lead to training in the wrong zone. Ignoring individual variation in maximum heart rate is a third: the 220-minus-age estimate is a population average with meaningful person-to-person variation, so anyone doing serious performance training may want a lab-tested maximum heart rate instead.

Target Heart Rate Terms You Should Know

Heart Rate Reserve (HRR) — the difference between estimated maximum heart rate and resting heart rate; the basis of the Karvonen formula.

Resting Heart Rate (RHR) — heart rate at complete rest, best measured immediately upon waking before any activity.

Maximum Heart Rate (MHR) — the highest heart rate a person can safely achieve during exercise, commonly estimated as 220 minus age.

VO2 Max — a related, more precise measure of cardiovascular fitness based on oxygen consumption during exercise, typically requiring lab testing to measure directly.