Pregnancy Due Date Calculator: Your Complete Pregnancy Timeline
Our pregnancy due date calculator uses Naegele's rule, the standard method used by healthcare providers worldwide. By entering your last menstrual period (LMP) and average cycle length, you'll receive an estimated due date, current pregnancy week, trimester information, and a timeline of important milestones.
Remember that only about 5% of babies are born on their exact due date—it's an estimate, not a deadline. Most babies arrive within two weeks before or after. For fertility planning, see our Ovulation Calculator.
How Due Date Calculation Works
Naegele's Rule: Adds 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation on day 14. If your cycles are longer or shorter, the calculator adjusts accordingly.
Why LMP? While conception occurs around ovulation (typically day 14), LMP is easier to identify precisely. The two weeks before ovulation are counted as weeks 1-2 of pregnancy, which is why pregnancy is "40 weeks" despite gestation being approximately 38 weeks from conception.
Understanding Trimesters
First Trimester (Weeks 1-13): Major organ development, highest miscarriage risk, morning sickness common. Second Trimester (Weeks 14-27): Often called the "honeymoon period"—energy returns, baby movements felt. Third Trimester (Weeks 28-40): Rapid growth, baby gains most weight, preparation for birth.
FAQ
How accurate is this calculator?
As accurate as Naegele's rule allows—within a few days for regular cycles. Ultrasound dating in the first trimester is considered most accurate. Your healthcare provider may adjust your due date based on early ultrasound measurements.
What if I don't know my LMP?
An early ultrasound can determine gestational age. Your provider will measure the baby and calculate a due date from those measurements.