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Heart Rate Reserve (Karvonen) Calculator

Traditional heart rate zone calculations rely solely on age-predicted maximum heart rate, ignoring an individual’s resting cardiovascular fitness.

Your biological age in years.

Beats per minute measured at complete rest.

Target percentage of heart rate reserve (e.g. 70–80% for tempo runs).

Measured maximum heart rate from a stress test (leave 0 to use 220 - age).

Calculated Result
154 BPM (75% intensity)

Karvonen Target Heart Rate

Target Workout HR

154 BPM

Heart Rate Reserve

123 BPM

Max Heart Rate

185 BPM

Zone 2 (Aerobic Base)

136 – 148 BPM

Zone 4 (Threshold)

160 – 173 BPM

Calculation Breakdown

  1. Heart Rate Reserve (HRR)Max HR (185 BPM) - Resting HR (62 BPM) = 123 BPM reserve capacity.
  2. Karvonen Formula Target62 + (75% × 123) = 154 BPM.

Karvonen Heart Rate Spectrum (BPM)

Interactive visualization based on your current inputs

Calculated Value
0.04693139185Resting HRTarget HRMax HR

What Is the Heart Rate Reserve (Karvonen) Calculator?

The Heart Rate Reserve (Karvonen) Calculator determines tailored cardiovascular training heart rates for athletes and fitness enthusiasts.

It adjusts training intensity to reflect an athlete’s individual baseline resting pulse.

How Does the Heart Rate Reserve (Karvonen) Calculator Work?

The calculator computes maximum heart rate (220 - age or custom lab value).

It subtracts resting heart rate from max HR to determine Heart Rate Reserve (HRR).

It computes the target training heart rate and models all 5 distinct physiological training zones.

Heart Rate Reserve (Karvonen) Calculator Formula & Variables

The core mathematical equation utilized by this calculator is expressed as:

HR_{\text{target}} = HR_{\text{rest}} + \%\text{Intensity} \times (HR_{\text{max}} - HR_{\text{rest}})

Heart Rate Reserve (HRR) is calculated by subtracting resting heart rate from maximum heart rate, multiplying by desired training intensity, and adding back resting heart rate.

How to Use the Heart Rate Reserve (Karvonen) Calculator

  1. Enter your current age and morning resting heart rate in BPM.
  2. Select your desired workout intensity percentage.
  3. Review target BPM and programming zones for your smartwatch or chest strap.

Step-by-Step Example Calculation

35-Year-Old with 62 BPM Resting Pulse at 75% Intensity

Input Values:

age:35
restingHeartRate:62
intensityPct:75
customMaxHr:0
Worked Steps: Calculates Karvonen training zones for a 35-year-old with a 62 BPM resting pulse.

Understanding Your Result

The primary display reports your exact target workout heart rate in beats per minute.

The summary breaks down Zone 2 Aerobic Base and Zone 4 Lactate Threshold training zones.

Factors That Affect the Result

  • Cardiovascular conditioning: Highly conditioned athletes have lower resting heart rates and wider reserves.
  • Beta-blockers and medication: Blood pressure medications intentionally blunt maximum heart rate response.

When Should You Use This Calculator?

  • When programming marathon, cycling, triathlon, or HIIT cardio workouts.
  • When setting customized heart rate zones in fitness smartwatches.

Assumptions & Limitations

  • The 220 - age formula is a population average with a standard deviation of ±10–12 BPM.

Frequently Asked Questions

Calculation Accuracy & Reference Note

A formal laboratory graded treadmill or cycle ergometer VO2 max test provides the most accurate max HR measurement.

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