ForHosting KIT · Developer Utilities

Due date from CRL ultrasound calculator

This due date from CRL ultrasound calculator turns a first-trimester crown-rump length measurement into estimated gestational age and, when you supply the scan date, a calendar estimated due date.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

It applies the classic Robinson–Fleming dating formula used widely in obstetric ultrasound teaching: gestational age in days equals 8.052 times the square root of CRL in millimetres, plus 23.73. From that age the tool counts forward to a standard 280-day pregnancy length so you can see how many days remain until the educational due date and, with a scan date, the ISO calendar day for the EDD, an LMP estimate, and a simple conception estimate. The path is fully deterministic—no network calls, no random sampling, and no dependence on the server clock—so homework keys, LMS items, and CI fixtures match every time for the same CRL. Enter length in millimetres or centimetres, optionally add the ultrasound date as YYYY-MM-DD, and read back normalized millimetres, weeks-plus-days display, formula string, and ordered steps. The free browser run on this page uses the same pure module as the API. Failed validation is not billed; each successful API estimate costs $0.002. Treat the output as an educational and engineering estimate, not a clinical diagnosis or substitute for professional obstetric judgment.

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 due date from CRL ultrasound 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.

Which formula does this tool use?

Robinson–Fleming 1975: gestational age in days = 8.052 × square root of CRL in millimetres + 23.73. The educational due date uses a 280-day pregnancy length from the implied LMP.

Is the ultrasound scan date required?

No. CRL alone returns gestational age and days remaining to a 280-day EDD. Supply scan_date (YYYY-MM-DD) when you need calendar due_date, lmp_estimate, and conception_estimate.

Can I enter CRL in centimetres?

Yes. Set unit to cm (or length_unit / measure_unit). The length is converted to millimetres before the Robinson–Fleming formula.

Is this medical advice or a diagnostic tool?

No. The result is an educational and engineering estimate from published coefficients. Clinical dating decisions need professional obstetric interpretation and institutional protocols.

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/health/due-date-crl

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/health/due-date-crl \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"crl":32}'

const res = await fetch("https://api.kit.forhosting.com/health/due-date-crl", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "crl": 32
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/health/due-date-crl",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "crl": 32
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/health/due-date-crl", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"crl":32}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"crl":32}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/health/due-date-crl", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "crl": 32
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "health.due_date_crl",
  "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 →