Due date from CRL ultrasound calculator
A crown-rump length of 32 mm on a scan dated 15 March 2026 puts the pregnancy at 9 weeks and 6 days, with an estimated due date of 12 October 2026. It applies the Robinson–Fleming formula as an educational estimate. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Crl
- 32
- Scan date
- 2026-03-15
- Crl mm
- 32 mm
- Gestational age days
- 69.279
- Gestational weeks
- 9
- Gestational days rem
- 6
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. 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. 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. Treat the output as an educational and engineering estimate, not a clinical diagnosis or substitute for professional obstetric judgment.
What crown-rump length dating tells you
Crown-rump length is the straight-line measurement from the top of the fetal head to the bottom of the rump on a first-trimester ultrasound image, typically expressed in millimetres. In early pregnancy CRL correlates tightly with gestational age, which is why clinical protocols often prefer CRL-based dating over last-menstrual-period dates when the two disagree.
This calculator implements the Robinson–Fleming 1975 regression that maps CRL in millimetres to gestational age in days with a square-root formula, then reports that age as total days, whole weeks, remaining days within the week, and a compact display such as 10w+2d. The pregnancy clock used for the educational due date is the common 280-day (forty-week) length counted from a notional last menstrual period: days remaining until the due date equal 280 minus gestational age in days.
When you omit the scan date, the response still returns gestational age and the relative days-to-due figure so scripts can store relative dating without inventing a calendar. There is no growth percentile chart, no twin adjustment, no nuchal translucency term, and no biometry-based fetal weight in this contract—those belong to other tools.
Where a CRL due-date calculator earns its keep in education and software
Sonography and midwifery coursework introduce Robinson–Fleming dating when textbooks walk through early ultrasound and ask learners to convert a single CRL into weeks-plus-days and an estimated due date. Product teams call the same contract from scripts to seed deterministic test vectors for prenatal dashboards, to validate user-entered ultrasound fields before related tools run, or to satisfy programming-challenge statements that demand CRL-based dating rather than a black-box mobile app.
Clinical-engineering demos sometimes show CRL dating beside an LMP-based due date purely as a teaching contrast, while reminding readers that real dating policy depends on local protocols, serial scans, and professional interpretation. Treat the output as an educational and engineering estimate: if clinical accuracy is required, prefer your institution’s ultrasound package and a qualified clinician. Pair this tool with last-menstrual-period due-date calculators or estimated fetal weight tools when your worksheet needs related obstetric numbers, and keep units honest so millimetres and centimetres are never mixed by accident.
What you can do with it
Sonography coursework and exam checks
Convert a first-trimester CRL into Robinson–Fleming gestational age and an educational due date for labs, homework, and exam keys.
Ultrasound form demos and input validation
Normalize mm or cm CRL, reject missing lengths, and return weeks-plus-days plus optional calendar EDD for prototype report UIs.
FAQ
What does the due date from CRL ultrasound calculator cost?
It is free in your browser on this page.
Which formula does this tool use?
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.
Can I enter CRL in centimetres?
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.
Related tools
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
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
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. |
Technical notes
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.
What CRL dating means and what the response contains
When you include scan_date as YYYY-MM-DD, the engine adds the rounded remaining days with pure proleptic Gregorian arithmetic to produce due_date, subtracts gestational age for an LMP estimate, and places a simple conception estimate fourteen days after that LMP estimate. Optional fields that are not provided are omitted from the JSON rather than filled with null. Missing CRL, non-numeric length, non-positive values, or CRL outside the supported first-trimester millimetre window fail with invalid_input and field-named messages so a bad form cell never becomes a wrong due date.
How inputs are read and how results stay reproducible
Optional leading plus signs and scientific notation on numeric strings are allowed when they parse as finite decimals; embedded spaces, hex prefixes, and non-numeric tokens are rejected with a clear message. After conversion to millimetres, CRL must lie inside a practical window of two to one hundred millimetres that covers typical first-trimester dating while catching inverted unit mistakes. Computation evaluates the fixed Robinson–Fleming coefficients, rounds gestational age to four decimal places for stable goldens, splits floor days into weeks and remainder days, and rounds the day offset for calendar addition so due dates do not drift with floating-point noise. The preferred field is crl as a finite positive number, with aliases crown_rump, crown_rump_length, and length for form builders that prefer longer names. Optional unit accepts millimetres by default or centimetres so report sheets that print centimetres can post without multiplying by ten; a single unit applies to the one length on the request. Optional scan_date, with aliases ultrasound_date, exam_date, and date, must be a real civil date in YYYY-MM-DD form; impossible days such as the thirty-first of February are rejected. Pair the free browser run on this page with the priced API when you need the identical mathematical result inside an automated pipeline, LMS grader, or ultrasound worksheet demo that must not re-derive square roots by hand.
Where a CRL due-date calculator earns its keep in education and software
On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002, failed validation is not charged, and nothing is stored after the response returns. That split—free interactive exploration and a priced, identical API—matches the rest of the KIT tier-A catalog and lets you move from a classroom demo to an automated pipeline without changing the mathematical result.
Integration use cases
Deterministic fixtures for prenatal software
Generate stable gestational_age_display, days_to_due, and due_date fields for unit tests and CI without re-coding square-root dating.