Pregnancy Due Date Calculator
Due dates are arithmetic with a disclaimer: Naegele's rule adds 280 days to the first day of your last period, because the average pregnancy runs 40 weeks from that anchor. Enter an LMP date, a conception date (266 days), or an ultrasound reading with its gestational age and the calculator returns the estimated due date with its weekday, how far along you are today in weeks and days, the countdown, and which trimester you're in.
The date is remembered on this device, so each visit shows the current week without re-entering anything — the kind of page people genuinely come back to weekly. Two honest caveats travel with the answer: only about 5% of babies arrive on the due date itself (most come within two weeks of it), and first-trimester ultrasound dating beats LMP when cycles are irregular. This tool does the math your midwife will recognize; it doesn't replace them.
How to use
- Choose your method: last period, conception date, or ultrasound with gestational age.
- Enter the reference date (plus weeks and days for ultrasound).
- Read the due date, current gestational age, days remaining and trimester - it updates weekly on return visits.
Frequently asked questions
How is a due date calculated?
Naegele's rule: first day of the last menstrual period + 280 days, assuming a 28-day cycle with ovulation on day 14. From a known conception date it's 266 days; from a first-trimester ultrasound, the measured gestational age is subtracted from 280 to project the due date. All three methods are built in.
How accurate is a due date?
As a deadline, not very — roughly 5% of babies arrive on it, though most deliver between 37 and 42 weeks. As the midpoint that anchors every appointment, test and milestone, it works well, which is why clinicians redated pregnancies from early ultrasound when the two disagree by more than a week.
What gestational age am I today?
Weeks and days since the LMP date — 32w 3d means 32 weeks and 3 days of the 40-week term. The calculator computes this fresh on every visit against today's date, along with the trimester split at 13 and 27 completed weeks.
Does an irregular cycle change the due date?
Yes — Naegele assumes ovulation on day 14, so long or irregular cycles push the real conception date later and the LMP-based estimate early. If you know ovulation or conception, use those methods here, or trust a dating ultrasound over the calendar.