ForHosting KIT · Developer Utilities

Julian Day to date converter

This Julian Day to date converter takes a single astronomical Julian Day Number and returns the matching proleptic Gregorian calendar date plus Universal Time clock fields derived from the fractional day.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

The Julian Day is the continuous day count used in astronomy, ephemerides, and many scientific logs: JD zero point is noon Universal Time on the proleptic Gregorian date negative four thousand seven hundred thirteen November twenty-four, and every successive day increments the count by one. Whole numbers mark noon UT; a half fraction such as two million four hundred fifty-one thousand five hundred forty-four point five marks midnight at the start of the civil day. Small checks you may already know include two million four hundred fifty-one thousand five hundred forty-five point zero mapping to one January two thousand at twelve hours UT, the same integer minus zero point five mapping to that midnight, and two million four hundred forty thousand five hundred eighty-seven point five mapping to one January nineteen seventy at midnight UT. The engine uses only finite arithmetic with no network calls, no sampling, and no host-clock Date objects. Use it free in the browser for lab notes and teaching, or call the API at $0.002 per successful request when you need reproducible JD fixtures in CI, archives, 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/from-julian-day

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/from-julian-day \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"jd":2451545}'

const res = await fetch("https://api.kit.forhosting.com/date/from-julian-day", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "jd": 2451545
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/date/from-julian-day",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "jd": 2451545
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/date/from-julian-day", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"jd":2451545}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"jd":2451545}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/date/from-julian-day", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "jd": 2451545
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "date.from_julian_day",
  "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

`jd_min`	-1000000000
`jd_max`	1000000000

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