ForHosting KIT · Developer Utilities

Determine your cardio training zone from heart rate

This heart rate training zone calculator compares a current heart rate with an already computed maximum heart rate and identifies the matching level in the standard five-zone model.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

It reports the percentage of maximum, zone number, familiar zone name, intensity range, and whether the reading exceeds the supplied maximum. The calculation is deterministic and does not estimate maximum heart rate from age. Use the maximum value produced by your chosen method, test, clinician, coach, or device, then decide explicitly whether readings above that value should be accepted.

How to use it

Enter your values in the form above. The tool checks them before calculating and shows the result on the same page.

Check your inputs

Use the labels and units shown next to each field. If something is missing or outside the allowed range, the page points to the field to fix.

Use it again or automate it

Use the browser tool for individual checks and the API when you need the same capability in an automated workflow.

What you can do with it

Get an answer now

Enter one set of values and see the result without building a spreadsheet or script.

Compare scenarios

Change one value at a time and rerun the calculation to understand what affects the result.

Automate repeated work

Use the API when the same calculation needs to run inside your product or workflow.

FAQ

What does one calculation cost?

The API price is $0.002 per request. The same deterministic calculation can also run in the browser.

Does this calculate my maximum heart rate?

No. Supply a maximum heart rate computed or measured elsewhere; this capability only classifies the current reading against it.

What happens below 50% of maximum?

The result uses zone 0 with the label “Below zone 1,” making it clear that the reading is outside the five standard training zones.

Which zone gets an exact boundary value?

The higher zone gets the boundary. For example, exactly 60% is zone 2 and exactly 90% is zone 5.

Can the current heart rate exceed the maximum?

Only when allow_over_max is true. Otherwise the request returns invalid_input; when allowed, the result is zone 5 and over_max is true.

Is this medical advice?

No. It is a mathematical classification of supplied values and cannot assess health, sensor accuracy, or whether an exercise intensity is safe for an individual.

For developers — API access

Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.

API endpoint

POSThttps://api.kit.forhosting.com/fitness2/cardio-zone-from-hr

Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.

Call it from your stack

curl -X POST https://api.kit.forhosting.com/fitness2/cardio-zone-from-hr \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"current_heart_rate":152,"max_heart_rate":190}'

const res = await fetch("https://api.kit.forhosting.com/fitness2/cardio-zone-from-hr", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "current_heart_rate": 152,
    "max_heart_rate": 190
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/fitness2/cardio-zone-from-hr",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "current_heart_rate": 152,
    "max_heart_rate": 190
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/fitness2/cardio-zone-from-hr", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"current_heart_rate":152,"max_heart_rate":190}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"current_heart_rate":152,"max_heart_rate":190}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/fitness2/cardio-zone-from-hr", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "current_heart_rate": 152,
  "max_heart_rate": 190
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "fitness2.cardio_zone_from_hr",
  "status": "queued",
  "_links": {
    "result": "/tasks/tsk_…/result"
  }
}

The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.

Pricing

Per request$0.002

Published price — no tokens, no invented credits. A failed task is never charged.

Errors

HTTP	Code	Meaning
`401`	`unauthorized`	Missing or invalid API key.
`402`	`insufficient_balance`	Your balance doesn't cover the task price.
`404`	`unknown_type`	That task type doesn't exist.
`429`	`rate_limited`	Too many requests. Use the webhook instead of polling.

Read the full KIT documentation →