ForHosting KIT · Developer Utilities

Start and end of ISO week

This start and end of ISO week calculator takes a single Gregorian calendar date in YYYY-MM-DD form and returns the Monday that opens the ISO-8601 week containing that day and the Sunday that closes it.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

ISO weeks always run Monday through Sunday and never depend on locale first-day settings, which is why payroll, manufacturing packs, agile sprint labels, and cross-border reporting prefer them over US-style Sunday-start weeks. Classic checks include 2024-01-03 mapping to the week from 2024-01-01 through 2024-01-07, and 2021-01-01 mapping to the week from 2020-12-28 through 2021-01-03 because that Friday still belongs to week 53 of week-year 2020. The engine uses only deterministic integer calendar arithmetic: leap years, month lengths, ISO weekday, Julian Day Number offsets, and week-number boundary rules are computed without network calls, random sampling, or the host clock. Use it free in the browser for planning sheets and compliance checks, or call the API at $0.002 per successful request when you need reproducible week window bounds in CI, reporting pipelines, or product features.

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

How do I use this capability?

Complete the fields above and run it on this page. The form highlights anything that needs attention.

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/date/iso-week-start-end

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/date/iso-week-start-end \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"date":"2024-01-03"}'

const res = await fetch("https://api.kit.forhosting.com/date/iso-week-start-end", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "date": "2024-01-03"
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/date/iso-week-start-end",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "date": "2024-01-03"
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/date/iso-week-start-end", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"date":"2024-01-03"}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"date":"2024-01-03"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/date/iso-week-start-end", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "date": "2024-01-03"
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "date.iso_week_start_end",
  "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 →