ForHosting KIT · Developer Utilities

Jet lag recovery calculator

This jet lag recovery calculator estimates how many days your body may need to realign after crossing time zones, using a simple deterministic rule based on zones crossed and travel direction.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

Eastward trips force a phase advance of the circadian clock and are modeled at one full recovery day per zone, while westward trips allow a phase delay and are modeled at half a day per zone, matching a widely cited travel-medicine heuristic rather than a personalized medical plan. Enter six zones east and you get six recovery days; six zones west yields three; zero zones yields zero. Negative zone counts are rejected with invalid_input because a negative crossing is not a physical trip shift. The engine uses only finite arithmetic with no network calls, no sampling, and no date-dependent shortcuts. Use it free in the browser for trip planning and briefing notes, or call the API at $0.002 per successful request when you need reproducible recovery-day fixtures in booking tools, corporate travel apps, or CI.

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 the jet lag recovery calculator cost?

It is free in your browser on this page. Through the API a successful request costs $0.002; invalid inputs are not charged.

How are recovery days computed?

recovery_days = zones_crossed × days_per_zone. Eastward travel uses 1.0 day per zone; westward travel uses 0.5 day per zone.

What happens if zones_crossed is negative?

The input is rejected with invalid_input. A negative count of time zones does not describe a real trip shift.

Why is eastward recovery longer than westward?

Eastward travel requires a circadian phase advance (harder for most people). Westward travel is a phase delay, modeled here at half a day per zone.

Is this a medical diagnosis or sleep plan?

No. It is a deterministic rule-of-thumb estimate for planning only. Individual recovery varies with age, light exposure, sleep debt, and itinerary.

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/travel/jet-lag-recovery

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/travel/jet-lag-recovery \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"zones_crossed":6,"direction":"east"}'

const res = await fetch("https://api.kit.forhosting.com/travel/jet-lag-recovery", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "zones_crossed": 6,
    "direction": "east"
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/travel/jet-lag-recovery",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "zones_crossed": 6,
    "direction": "east"
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/travel/jet-lag-recovery", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"zones_crossed":6,"direction":"east"}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"zones_crossed":6,"direction":"east"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/travel/jet-lag-recovery", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "zones_crossed": 6,
  "direction": "east"
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "travel.jet_lag_recovery",
  "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.

Limits

max_zones 24

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 →

Run — free