Recovery

Heart Rate Zone Calculator

Calculate personalized heart rate training zones with the Karvonen method.

Karvonen Zones

Max HR: 190 bpm · HRR: 130 bpm

Training Zone Ladder

Each zone occupies a target heart-rate band between recovery and VO₂ max work.

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

125 bpm190 bpm

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

Formula: Karvonen method (target HR = resting HR + intensity × HRR).

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.
Read your five zones: Z1 (recovery), Z2 (aerobic base — conversational), Z3 (tempo — challenging), Z4 (threshold — hard), Z5 (VO2 max — maximum). Zone boundaries are estimates ±5 bpm.
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.

AI Integrations

Contract, discovery endpoints, and developer notes for agent use.

Always available for agents

Tool contract JSON

https://aifithub.io/contracts/heart-rate-zone-calculator.json

Stable input and output contract for this exact tool.

Human review

People can use the browser page to sense-check outputs and charts, but agents should still execute against the contract and discovery endpoints.

/agent-tools.json - machine-readable tool index.
/llms.txt - human-readable model discovery guide.
/.well-known/webmcp.json - WebMCP capabilities manifest.
/.well-known/ai-plugin.json - plugin-style discovery manifest.

{
  "tool": "heart_rate_zones",
  "age": 30,
  "resting_hr": 60,
  "method": "karvonen"
}

Open tool contract JSON Open AI integrations guide

Expand developer notes

Agent playbook

Resolve Heart Rate Zone Calculator from /agent-tools.json and open its contract before execution.
Validate inputs against the contract schema instead of scraping labels from the page UI.
Open the browser page only when a person wants to review charts, assumptions, or related tools.

Agent FAQ

Should ChatGPT, Claude, or another agent click through the UI?

No. Start with /agent-tools.json, then follow the tool's contract URL. The page UI is for human review, not parameter discovery.

When do tools show Quick and Advanced?

Every tool opens in Quick Start first. Advanced Controls keeps the same scenario, reveals more assumptions or diagnostics, and every tool keeps AI integrations inline below the instructions.

When should an agent still open the browser page?

Open it when a human wants to sense-check the output, review the chart, or keep exploring related tools after the calculation finishes.

Questions people usually ask

Which formula is used here?

Uses max heart rate and resting heart rate reserve (Karvonen) to build five intensity zones.

Can I use metric or imperial units?

Yes. This tool supports both metric and imperial units and remembers your preference.

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?

Yes. Every tool supports both systems and remembers your preference in localStorage.

Related Resources

Learn the decision before you act

Every link here is tied directly to Heart Rate Zone Calculator. Use the explanation, formula, examples, and benchmarks to pressure-test the calculator output from first principles.

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Guides · 3 Checklists · 3 Comparisons · 1 Learn · 2 Tips · 8

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