When the Pregnancy Due Date Calculator seems to misbehave, the cause is usually one of two things: something stopped the tool from running, or it ran but the result is not usable. This guide starts with the fastest checks, then walks through the common problems and exact fixes.
Quick Checks First
- Refresh the page - a stalled session is the most common cause of nothing happening.
- Confirm the input is not empty and actually contains what you meant to submit.
- Try the smallest possible input; if that works, the issue is size, not the tool.
- Turn off browser extensions that block scripts, then reload and test again.
- Update or switch browsers if the problem repeats across sessions.
Common Problems and How to Fix Them
My due date moved after a scan.
Early ultrasound dating is usually more precise - expect the estimate to be refined by clinicians.
My cycles are irregular so the date looks wrong.
The 280-day method assumes roughly 28-day cycles - irregular cycles widen the true window considerably.
I only know roughly when conception happened.
Use the conception-date method if you have a reliable date; otherwise the LMP route is standard.
The tool says 40 weeks but I feel further along.
Gestational age counts from the period, about two weeks before conception - check the weeks-along readout.
Only a small share of babies arrive on the due date.
Treat it as the centre of a window - most births land within a couple of weeks either side.
Is this medical advice?
No - confirm dates with your midwife or obstetrician; urgent concerns need clinical care, not a calculator.
When It Works but the Output Is Poor
If the tool runs fine but the result misses, the problem is almost always the brief, not the software:
- Treating the date as exact
- Using an uncertain period date
- Ignoring cycle length variation
- Confusing gestational age with embryo age
How to Stop It Happening Next Time
- Keep a saved prompt template for every task you repeat.
- Change one setting per generation so causes stay obvious.
- Run a two-minute sanity test with known input after any update.
- Note every failure and its fix; a short troubleshooting log pays for itself.
Still Stuck?
Reproduce the problem with the smallest possible input and note the exact steps that triggered it. A one-line description of what you did, what you expected and what happened is enough to get a precise answer from support or a colleague.
Frequently Asked Questions
How is the due date calculated?
From the first day of your last menstrual period, adding 280 days - the standard 40-week Naegele estimate.
How accurate is the estimate?
Only about 5 percent of births land on the exact day - real dating is confirmed by ultrasound.
What if I do not know my period date?
If you know a conception date you can work from that instead; otherwise ask your clinician for dating help.
Is my date stored?
No - the calculation stays in your browser.
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