ForHosting KIT · Developer Utilities

Birthday weekday calculator

This birthday weekday calculator answers a question people type every planning season: what day of the week does my birthday fall on in a given year?

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

You enter a birth date as an ISO calendar day and a target year. The engine copies the month and day onto that year, checks that the anniversary is a real Gregorian date, and returns the English weekday name. February 29 is accepted only when both the birth year and the target year are leap years, so a twenty-ninth of February in a common year is rejected instead of silently sliding to the twenty-eighth or the first of March. The same integer arithmetic powers the free browser widget and the API, with no host clock, no time zone, and no Date object, so two calls with the same inputs always return the same weekday. Use it when you already know the birth record and only need the weekday of that anniversary in another year.

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/life/birthday

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/life/birthday \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"date":"1990-07-25","year":2026}'

const res = await fetch("https://api.kit.forhosting.com/life/birthday", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "date": "1990-07-25",
    "year": 2026
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/life/birthday",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "date": "1990-07-25",
    "year": 2026
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/life/birthday", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"date":"1990-07-25","year":2026}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"date":"1990-07-25","year":2026}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/life/birthday", 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": "1990-07-25",
  "year": 2026
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "life.birthday",
  "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

`year_min`	1
`year_max`	9999

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 →