Due Date Calculator for your website
Estimated due date from a last menstrual period or a known conception date, with the current gestational age. Set the values it should open on, then copy the iframe. Your visitors can change them; the widget recomputes against Rule Calculator and never touches your page.
Who puts this on their site
Midwifery practices, parenting sites and pregnancy trackers, on Naegele’s rule with the cycle-length correction most calculators skip.
Free for commercial use. No key, no account, no tracking script, and nothing loaded from a third party — the iframe points at Rule Calculator and that is the only request it makes. The formula and its source travel with it, so the number on your page is one your readers can check.
Opening values
Set what the widget shows before anyone touches it. Leave a field as it is and it stays out of the URL.
Preview
Paste this
<iframe src="https://rulecalculators.com/embed/due-date" width="100%" height="940" style="border:1px solid #e5e5e5;border-radius:12px" loading="lazy" title="Due Date Calculator"></iframe>
<p style="font:13px/1.5 system-ui,sans-serif;color:#666;margin:6px 0 0"><a href="https://rulecalculators.com/calc/due-date" style="color:#666">Due Date Calculator</a> by <a href="https://rulecalculators.com" style="color:#666">Rule Calculator</a></p>Free for commercial use. The one condition is the credit link inside the widget, which is how the calculator stays free. Want the numbers in your own markup instead? The same calculator is a JSON endpoint, or see the full Due Date Calculator page with its sources and working.