Enter the first day of your last menstrual period or your conception date to calculate your estimated due date and pregnancy timeline.
Key milestones
Due dates are estimates. Only about 5% of babies are born on their exact due date. Most are born within 2 weeks before or after.
The most common method is Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle with ovulation on day 14.
If your cycle is longer or shorter than 28 days, the due date shifts accordingly. A 35-day cycle means ovulation likely occurred around day 21 instead of day 14, pushing the due date back by a week. This pregnancy calculator adjusts for your actual cycle length.
If you know your conception date, the calculation is simpler: add 266 days (38 weeks) from conception. Conception-based dates tend to be more accurate because they eliminate the cycle-length variable.
First trimester (weeks 1–12): The embryo develops all major organs. Morning sickness peaks around weeks 8–10. The risk of miscarriage drops significantly after week 12. The first ultrasound typically happens around week 8–12.
Second trimester (weeks 13–27): Often called the "honeymoon period" — energy returns, nausea fades. You'll start showing and feeling movement (quickening) around weeks 16–20. The anatomy scan at week 20 checks all major structures.
Third trimester (weeks 28–40): Baby gains most of its weight. Braxton-Hicks contractions may start. The baby typically moves into head-down position by week 36. "Full term" begins at week 39.
Due date calculators based on LMP are accurate within about 1–2 weeks. Only about 5% of babies arrive on the exact due date. About 80% are born between weeks 38 and 42. An early ultrasound (before 12 weeks) provides the most accurate dating.
If you don't know your LMP, an ultrasound in the first trimester can estimate gestational age based on the baby's size. This is actually more accurate than LMP-based calculations, especially for women with irregular cycles.
Yes. The standard calculation assumes a 28-day cycle. If your cycle is 35 days, ovulation likely occurred a week later, pushing your due date back by about a week. This calculator adjusts for your actual cycle length.
The American College of Obstetricians and Gynecologists defines full term as 39 weeks 0 days through 40 weeks 6 days. Early term is 37–38 weeks, late term is 41 weeks, and post-term is 42+ weeks.
Yes. If an early ultrasound shows the baby measuring significantly different from the LMP-based estimate (more than 5–7 days), your provider may adjust the due date based on the ultrasound measurements.