Heart Rate Reserve Calculator (Karvonen)
This calculator shows your personalized training zones and target heart rate using Heart Rate Reserve (HRR). It’s useful whenever you want intensity targets that account for your resting heart rate rather than using crude % of max alone.
The Heart Rate Reserve (Karvonen) Calculator allows you to build a complete zone table from your resting and maximum heart rate (or your age if you don’t know max). The goal is to tailor workout intensity to your physiology so you can train precisely—easy days truly easy, threshold days on point, and hard sessions structured to your objectives. Enter your numbers below to get started.
Enter your resting heart rate and either an age-based estimate of max heart rate or a measured max. We’ll build Karvonen (HRR) zones and compute a specific target heart rate for any intensity you choose.
Morning resting value is best.
Common aerobic work ~60–75% HRR.
Tanaka often fits adults better.
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Karvonen Zone Table
Ranges use Heart Rate Reserve percentages. Train by zone to target specific adaptations.
Heart Rate Reserve results interpretation
How it works
Show formulas
Max HR (age-based): Fox: 220 − age; Tanaka: 208 − 0.7×age.
Heart Rate Reserve: HRR = HRmax − HRrest.
Target HR: THR = HRrest + %×(HRmax − HRrest).
Formulas, assumptions, limitations
Personalization. HRR accounts for your resting HR; two athletes with the same max can have different targets.
Zone model. We display 5 common zones: 50–60, 60–70, 70–80, 80–90, 90–100% HRR.
Specific target. Use the intensity slider to get a single-session target HR.
Methods. Choose Tanaka or Fox for age-based max, or enter a measured max HR.
Limitations. Medications, dehydration, heat, and fatigue can shift HR. Use perceived exertion and pace too.
Use cases & examples
Select 65% HRR and hold the target HR for aerobic base building.
Target 75–80% HRR for sustained threshold efforts.
Work at 90–95% HRR with full recovery back toward Z1–Z2 between reps.
Karvonen / HRR FAQs
Is HRR better than % of max HR?
Often, yes. HRR incorporates resting HR, giving more individualized targets than raw % of max HR.
Which max HR formula should I use?
Tanaka (208 − 0.7×age) tends to fit many adults better than 220 − age, but a measured max is best.
What if my resting HR changes?
Update your resting HR periodically (e.g., morning values). Lower resting HR will reduce target HR at the same %HRR.
Can medications affect training HR?
Yes. Beta blockers and other agents can lower HR response. Consult your clinician for guidance.
Should I train only by HR?
Combine HR with pace/power and perceived exertion. Heat, hydration, and drift can move HR during long efforts.
Heart Rate Reserve (Karvonen): A Complete Guide to Personalized Training Zones
Training by heart rate can be as simple or as sophisticated as you make it. The simplest approach— using a flat percentage of maximum heart rate—ignores one critical piece of information: your resting heart rate. Heart Rate Reserve (HRR), also known as the Karvonen method, explicitly incorporates resting heart rate to personalize the intensity zones you use in training. In this guide we’ll unpack why HRR is helpful, how to measure the inputs, how to set zones for different sports, and how to put the numbers to work through common workouts.
Why use HRR instead of raw % of max?
Two athletes can share the same max heart rate yet have very different resting values. If Athlete A has a resting HR of 45 bpm and Athlete B rests at 65 bpm, then “70% of max” will land them at very different relative intensities. HRR aligns the prescription with the gap between resting and max, so the same %HRR represents a similar physiological load for both athletes. That precision helps keep easy days easy and hard days appropriately hard, improving recovery and consistency.
Inputs: resting and max heart rate
- Resting HR: Measure in the morning, after waking, before caffeine. Use the lowest stable reading across several mornings. Changes over weeks can indicate fitness or fatigue.
- Max HR: Best from a lab test or hard field test (e.g., graded hill reps). If you don’t have one, estimate from age. Tanaka’s 208 − 0.7×age often fits adults better than 220 − age.
A practical five-zone model
There are many zone systems. A widely used five-zone HRR scheme is:
- Z1 (50–60% HRR): Very easy. Recovery and long conversational aerobic work.
- Z2 (60–70% HRR): Endurance. Aerobic base, fat oxidation emphasis.
- Z3 (70–80% HRR): Tempo. “Comfortably hard” steady efforts; strong aerobic stimulus.
- Z4 (80–90% HRR): Threshold. Lactate threshold work; sustained intervals.
- Z5 (90–100% HRR): VO₂ developments; short intervals and hill reps.
Workouts by zone
HR is slow to ramp compared with pace or power, but it remains a valuable anchor for steady-state sessions, long intervals, and heat/humidity management. Combine HR targets with RPE and, if available, pace or power for a robust, real-world prescription.
- Endurance run/ride: 45–120 minutes in Z2.
- Tempo set: 2×20 minutes in high Z3 with short recoveries.
- Threshold intervals: 4×8 minutes at Z4, 2–3 minutes easy between.
- VO₂ reps: 6×3 minutes in Z5, recoveries equal to work.
- Recovery day: 20–40 minutes in Z1, truly easy.
Cardiac drift, heat, and hydration
During long efforts, HR can rise at a constant pace due to heat, dehydration, and fatigue—known as cardiac drift. In hot environments, a pace or power that’s easy on a cool day might push HR into higher zones. Use HR to keep the session’s stress aligned with the plan; if drift is large, slow down, take fluids, and seek shade.
Measuring resting HR and tracking trends
Wearables can report overnight lows; manual spot checks work too. Watch for persistent drops (often fitness) or rises (possible stress or illness). Update the calculator when your resting HR changes by more than ~3–5 bpm over several weeks.
Different sports, different HR response
Running generally elicits higher HR for a given metabolic cost than cycling or swimming. If you train across sports, build sport-specific zones or at least sanity-check with RPE and performance metrics for each discipline.
Field testing max HR (caution)
A safe field protocol might include a progressive warm-up followed by repeated uphill efforts, ending with a hard final rep. However, testing to true maximum is physically demanding. If you have cardiovascular risk factors or are new to training, consult a clinician first.
Medications and medical considerations
Beta blockers and other medications can blunt heart-rate response; patients should follow medical guidance. In such cases, perceived exertion and talk test may be more reliable than numeric HR targets alone.
Putting it together
HRR-based zones anchor day-to-day training with a personal baseline. Pair them with a weekly mix of intensities, adequate recovery, and progressive volume to see steady improvement over months.
Quick answers
- How often should I update resting HR? Every few weeks or when it changes by ~3–5 bpm.
- Can HR zones replace pace or power? No—use them together. HR shines for steady efforts and heat management.
- Is Tanaka always better? Not always, but it’s often closer for adults. A measured max is best.
Key takeaways
- HRR personalizes intensity using your resting HR.
- Use five practical zones for clarity and consistency.
- Combine HR with RPE and pace/power to handle drift and conditions.
- Update inputs as your fitness and resting HR evolve.