Heart Rate Reserve Formula
Reference for the Heart Rate Reserve (HRR) formula and the Karvonen method.
Calculate personalized training heart rate zones for any fitness intensity level.
The Formula
Heart Rate Reserve is the gap between your maximum and resting heart rate — your usable cardiovascular range during exercise.
Karvonen Target Heart Rate
Use this to find the exact heart rate that corresponds to any training intensity percentage.
Maximum Heart Rate Estimate
This is a widely used estimate. For greater accuracy, measure your max HR during an all-out effort test under supervision.
Calculator
Variables
| Symbol | Meaning | Unit |
|---|---|---|
| HRR | Heart Rate Reserve | bpm |
| HRmax | Maximum heart rate | bpm |
| HRrest | Resting heart rate | bpm |
| Intensity% | Desired training intensity as a decimal | 0–1 |
| Target HR | Heart rate to aim for during training | bpm |
Example 1 — Calculate HRR
A 35-year-old athlete with a resting HR of 55 bpm.
HRmax ≈ 220 − 35 = 185 bpm
HRR = 185 − 55 = 130 bpm
Heart Rate Reserve = 130 bpm
Example 2 — Zone 2 Target HR
Using the same athlete, find Zone 2 (65% intensity) target HR.
Target HR = 55 + (0.65 × 130)
Target HR = 55 + 84.5
Target HR ≈ 140 bpm for Zone 2 aerobic training
Karvonen Training Zones
| Zone | HRR % | Purpose |
|---|---|---|
| Zone 1 | 50–60% | Recovery and warm-up |
| Zone 2 | 60–70% | Aerobic base building |
| Zone 3 | 70–80% | Aerobic threshold |
| Zone 4 | 80–90% | Lactate threshold |
| Zone 5 | 90–100% | VO2 Max / max effort |
When to Use It
- Setting personalized training zones for any sport
- Ensuring recovery runs stay truly easy
- Structuring interval and threshold workouts precisely
- Monitoring cardiovascular fitness over time
Key Notes
- Heart Rate Reserve: HRR = HRmax − HRrest: Karvonen formula for target HR: Target = HRrest + (HRR × intensity%). This is more accurate than simple %HRmax because it accounts for individual resting heart rate, giving a personalized training zone.
- HRmax estimation: The classic 220 − age formula has a standard deviation of ~10–12 bpm — large enough to make it unreliable for individuals. The Tanaka formula (208 − 0.7 × age) is more accurate. Direct measurement via a maximal exercise test is most reliable.
- Zone calculation example: A 40-year-old with HRrest = 60 bpm: HRmax ≈ 180, HRR = 120. Zone 2 at 60–70% HRR: target = 60 + (120 × 0.60) to 60 + (120 × 0.70) = 132–144 bpm. Using raw %HRmax gives a different (less personalized) range.
- Cardiac drift: During prolonged exercise, heart rate rises even at constant workload (dehydration, heat, fatigue). Using power or pace as the primary training target and HR as secondary avoids chasing a drifting HR on long sessions.
- Applications: HRR-based zones are used to prescribe rehabilitation exercise, set endurance training intensities, monitor recovery status (elevated resting HR signals incomplete recovery), and personalize fitness programming for athletes and cardiac patients.