Your estimated due date, current week, and trimester.

How is the due date calculated?

By default this uses Naegele's rule: the first day of your last menstrual period (LMP) plus 280 days (40 weeks), adjusted for a cycle length other than 28 days. The conception-date and IVF transfer-date methods convert to an equivalent LMP date first (conception ≈ LMP + 14 days; a day-5 blastocyst transfer ≈ LMP + 19 days), then apply the same 280-day rule.

Why does pregnancy get counted from before conception?

Medical convention counts gestational age from the first day of the last menstrual period, not from conception (which happens roughly two weeks later) — so you're considered a couple of weeks "pregnant" before conception technically occurs. This is standard obstetric practice, not an error in this calculator.

How accurate is this due date?

Only about 5% of babies arrive exactly on the estimated due date — it's a statistical midpoint of a normal range (most births happen within about 2 weeks either side), not a firm prediction. A first-trimester dating ultrasound is generally considered more accurate than a last-period calculation alone, especially if your cycles are irregular.

What are the trimester boundaries?

First trimester: weeks 1–13. Second trimester: weeks 14–26. Third trimester: week 27 onward until birth around week 40. "Full term" begins at week 37, and week 24 is commonly cited as a viability milestone in medical literature.