Cardio
Heart Rate Zone Calculator
Five heart rate training zones from your age and resting heart rate, by the Karvonen heart-rate-reserve method or as a percentage of max.
Result
Your zones (Karvonen)
| Zone 1 (Recovery) | 125–138 bpm |
| Zone 2 (Endurance) | 138–151 bpm |
| Zone 3 (Tempo) | 151–164 bpm |
| Zone 4 (Threshold) | 164–177 bpm |
| Zone 5 (VO2 Max) | 177–190 bpm |
Training zones
Target heart rates across the five training intensity bands.
Formula from Karvonen (1957) and Tanaka HRmax revisited (2001), checked against the source on May 25, 2026.
What does the Heart Rate Zone Calculator calculate, and which formula does it use?
The Heart Rate Zone Calculator builds five training zones with the Karvonen heart-rate-reserve method: max heart rate is estimated as 220 − age, heart-rate reserve is max HR minus resting HR, and each zone adds 50–100% of that reserve back onto resting HR — from Zone 1 recovery (50–60%) up to Zone 5 VO2 max (90–100%).
Last updated .
How to use it
- Measure resting heart rate immediately after waking before getting out of bed (count pulse for 60 full seconds). Average 3 consecutive mornings for the most reliable baseline input for the Karvonen formula.
- Enter your age and resting heart rate, and your measured max heart rate if you know it (otherwise pick 220 − age or Tanaka's 208 − 0.7 × age). Read your five zones: Z1 recovery, Z2 aerobic base (conversational), Z3 tempo, Z4 threshold, Z5 VO2 max. Age-based max estimates are typically off by about 10 bpm, so treat the boundaries as approximate.
- Zone 2 is underused by most recreational athletes. Spending 70–80% of weekly training volume in Zone 2 (you can speak in full sentences) builds aerobic base, improves fat oxidation, and reduces injury risk over the long term.
- High-intensity work (Zone 4–5) should occupy no more than 20% of total training volume. More than this without sufficient Zone 2 base leads to performance plateau and elevated injury risk.
- Re-run this calculator every 2–3 months of consistent training. Improved cardiovascular fitness lowers resting heart rate, which shifts all zone boundaries — keeping your intensity calibrated to current fitness level.
Questions people usually ask
Which formula is used here?
By default the Karvonen method: each zone is resting heart rate plus 50–60%, 60–70%, 70–80%, 80–90% or 90–100% of your heart rate reserve (max minus resting). You can switch to a plain percentage of max. Max heart rate is 220 − age by default, Tanaka's 208 − 0.7 × age as an option, or your own measured max.
Can I use metric or imperial units?
Heart rate is beats per minute in every system, so there is nothing to convert on this tool.
Is this medical advice?
No. This tool provides general fitness estimates and should not replace medical guidance.
Is this tool free and private to use?
Yes. AI Fit Hub tools are free, no-signup browser tools. Inputs stay in your browser unless you choose to share a URL.
Do these tools replace medical guidance?
No. These outputs are general fitness estimates — not medical advice.
Can I switch between metric and imperial units?
Tools that take weights, heights or distances have a Metric/US switch that remembers your choice; heart rate zones are in beats per minute either way.
The formula, worked through
- Formula Heart Rate Zone Formula (Karvonen)
Heart rate zone formula (Karvonen): target_HR = (HRmax − HRrest) × intensity_pct + HRrest. HRmax ≈ 208 − 0.7·age (Tanaka).
- Formula Cycling FTP Power Zones Formula
Computes Coggan cycling power zones as percentages of FTP, from active recovery near 55% up to anaerobic above 120%, with FTP from a 20-minute test.
- Formula Resting Heart Rate Formula and Percentile Chart
Resting heart rate rating: your seated pulse compared with U.S. NHANES percentiles for age and sex, from Athlete (lowest 5%) to Poor (above the 90th percentile).
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By goal
Use it from code
The same calculation as a JavaScript module you can import. It runs where you import it, with no request, key or rate limit.
import { compute } from "https://aifithub.io/engines/heart-rate-zone-calculator.js";Input and output contract, TypeScript types and the guide for agents.