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 far off can this be?
In 3,320 healthy adults who reached a verified maximum on an exercise test, age alone predicted maximal heart rate with a standard error of 10.8 beats a minute, whatever their sex, fitness or BMI, and the older formulas underestimated it for people over 30.
For a 30-year-old, the calculator's default 220 − age gives 190 bpm. With a standard error of 10.8 bpm, about two in three people of that age have a maximum between 179 and 201 bpm, and every zone shifts with it.
If you know your own maximum from a hard effort or a lab test, enter it: that removes this error from every zone.
Source: Nes et al. 2013, Scand J Med Sci Sports, “Age-predicted maximal heart rate in healthy subjects: The HUNT fitness study” .
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.
- Elite endurance athletes do about 80% of their sessions at low intensity (Seiler 2010). Easy Zone 1-2 work, where you can speak in full sentences, builds the aerobic base and is easy to recover from.
- Keep hard Zone 4-5 work to a minority of sessions, around 20% in the elite pattern, so each hard session gets full effort and the easy days stay easy.
- 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.
How accurate is 220 minus age?
It is a population average. In a meta-analysis of 351 studies, Tanaka and colleagues found 208 − 0.7 × age fitted adults better, especially over 40, and individual maximums still scatter around any formula by about 10 bpm. A measured max from a hard, all-out effort makes every zone more accurate.
Should I use Karvonen or percent of max?
Karvonen uses your resting heart rate as well, so the zones shift as you get fitter and your resting rate falls; percent-of-max zones are simpler and ignore it. For most people training by feel and heart rate together, Karvonen gives the more individual bands.
Do I need to convert units?
No. 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.
The formula, worked through
- Formula Resting Heart Rate Formula and Percentile Chart
Resting heart rate rating: your seated pulse against 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 an agent or code
Any agent can run this calculator by URL: put the inputs in the query string and get JSON back, with the inputs that used defaults and a line to cite (add format=md for markdown). MCP clients reach it through https://aifithub.io/mcp.
In code, import the same module; it runs where you import it, with no request or key.
import { compute } from "https://aifithub.io/engines/heart-rate-zone-calculator.js";Input and output contract, TypeScript types and the guide for agents.