Use this free Heart Rate Reserve (HRR) calculator to estimate your target training heart rate with the Karvonen method. Enter your age, resting heart rate, and desired workout intensity.
What is heart rate reserve?
Heart Rate Reserve (HRR) is the difference between your maximum heart rate and your resting heart rate. It is one of the most practical ways to personalize cardio training, because it accounts for your current fitness level better than simple “percent of max heart rate” formulas.
If two people are the same age, they may have similar estimated maximum heart rates. But if one person has a resting heart rate of 50 bpm and the other has 75 bpm, their cardiovascular systems are not the same. HRR captures that difference.
HRR formula (Karvonen method)
Step 1: Estimate max heart rate
Most calculators use:
Max HR = 220 − age
If you have a lab-tested max heart rate or reliable field test result, use that instead.
Step 2: Calculate reserve
HRR = Max HR − Resting HR
Step 3: Find target training heart rate
Target HR = Resting HR + (Intensity × HRR)
Intensity is written as a decimal. For example, 70% = 0.70.
Why coaches use HRR zones
Heart rate reserve zones are useful for endurance training, general fitness plans, and return-to-exercise programs. They help you avoid two common mistakes:
- Going too hard on easy days
- Staying too easy on days intended for threshold or interval work
In simple terms, HRR zones make your effort targets more realistic for your body.
Typical HRR training zones
- Zone 1 (50–60%): Recovery, very easy movement
- Zone 2 (60–70%): Aerobic base building, conversational pace
- Zone 3 (70–80%): Moderate tempo effort
- Zone 4 (80–90%): Hard work near threshold
- Zone 5 (90–100%): Very hard intervals, short durations
How to measure resting heart rate correctly
For best accuracy, measure resting heart rate first thing in the morning before caffeine, stress, or activity changes your pulse.
- Take your pulse for a full 60 seconds (or use a wearable)
- Repeat over 3–7 mornings
- Use the average value in this calculator
Example calculation
Suppose you are 40 years old with a resting heart rate of 60 bpm, and you want a 75% intensity target:
- Estimated Max HR = 220 − 40 = 180 bpm
- HRR = 180 − 60 = 120 bpm
- Target HR = 60 + (0.75 × 120) = 150 bpm
So your 75% effort target is approximately 150 bpm.
HRR vs. percent max heart rate
Percent max heart rate uses only age-based max HR. HRR includes your resting pulse, making it more individualized. For many people, that means better workout pacing and less guesswork.
Important safety notes
This calculator is for educational and general fitness planning purposes. It is not a diagnostic tool and does not replace medical advice.
- If you have heart disease, blood pressure concerns, chest pain, or dizziness, talk to a clinician before training with heart rate zones.
- Medications such as beta blockers can affect heart rate response.
- Hydration, heat, stress, sleep, and illness can all alter heart rate on a given day.
Bottom line
A heart rate reserve calculator gives you a smarter cardio target by combining resting and maximum heart rate. Use it to train with purpose: easy days easy, hard days hard, and better long-term progress.