Pregnancy Due Date Calculator
About This Calculator
This pregnancy due date calculator estimates your expected delivery date using either the first day of your last menstrual period (LMP) or your known conception date. The LMP method applies Naegele's rule, adding 280 days (40 weeks) to the start of your last period. The conception method adds 266 days (38 weeks) from the date of conception. Results include your current gestational age, trimester, days remaining, and key milestones throughout the pregnancy. Keep in mind that only about 5% of babies are born on their actual due date; most arrive within two weeks before or after.
FAQ
How accurate is the estimated due date?
Due date estimates are approximate. Only about 5% of babies arrive on the predicted date. Most births occur within a window of two weeks before or after the due date. An ultrasound performed in the first trimester can refine the estimate to within about five days.
What are the three trimesters?
The first trimester spans weeks 1 through 12, covering early development and organ formation. The second trimester runs from week 13 through week 27, when the baby grows rapidly and movements become noticeable. The third trimester lasts from week 28 until delivery, when the baby gains weight and prepares for birth.
What is Naegele's rule?
Naegele's rule is the standard method for estimating a due date. It adds 280 days (40 weeks) to the first day of the last menstrual period. This assumes a regular 28-day cycle with ovulation occurring on day 14. For irregular cycles, the estimate may be less accurate.
What does "full term" mean?
A pregnancy is considered full term from 37 weeks onward. Early term is 37-38 weeks, full term is 39-40 weeks, late term is 41 weeks, and post-term begins at 42 weeks. Babies born at 39 weeks or later generally have the best health outcomes.