What the results show
- Estimated due date — the day your baby is most likely to arrive, roughly 40 weeks after the first day of your last period.
- Gestational age — how far along the pregnancy is today, in weeks and days, counted from your last period.
- Trimester — which of the three stages of pregnancy you are currently in.
- Estimated conception — the approximate day conception occurred, based on your cycle length.
How the due date is calculated
The calculator uses Naegele's rule: it adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). Because the rule assumes a standard 28-day cycle with ovulation around day 14, the calculator also adjusts for your cycle length — a longer cycle pushes the due date later, a shorter one brings it earlier. Estimated conception is placed about 14 days before your next expected period.
This result is an estimate. Only around 1 in 20 babies is born on the exact due date, and an early ultrasound often gives a more accurate date than the last period alone. Always confirm with your healthcare provider.
Frequently asked questions
How accurate is the estimated due date?
It is a well-established estimate, but not a guarantee. A normal birth can happen any time from about three weeks before to two weeks after the due date. A dating ultrasound in the first trimester is usually the most reliable way to confirm it.
What if my cycle isn't 28 days?
Enter your own average cycle length in the cycle field. The calculator shifts the due date by the difference from 28 days, since ovulation — and therefore conception — happens later in a longer cycle and earlier in a shorter one.
What's the difference between the due date and conception date?
The due date and gestational age are measured from the first day of your last period, which is the medical convention. Actual conception happens roughly two weeks later, so the estimated conception date shown here is about two weeks after your period started.
Why do I see a dash instead of a due date?
The last-period date must be a valid date in the past, and the cycle length must be between 20 and 45 days. A future date, an incomplete entry, or an out-of-range cycle shows a dash until you fix it.
Is my information saved or uploaded?
No. The calculator runs entirely in your browser. Nothing you enter is stored or sent to a server.