Clinical Calculator
Due Date Calculator — Pregnancy Week & EDD Finder
Calculate your pregnancy due date, current gestational week, and trimester timeline based on your last menstrual period (LMP).
How is Due Date Calculated?
Estimating your due date helps track fetal development milestones and prepare for delivery. A standard pregnancy lasts approximately 40 weeks (280 days) from the first day of your last menstrual period (LMP).
Naegele's Rule
This calculator utilizes Naegele's Rule, the standard clinical formula. The calculation takes the first day of your LMP, adds 280 days, and adjusts for your average menstrual cycle length. If your cycle is longer than the standard 28 days, your ovulation occurred later, extending the estimated due date accordingly.
Trimester Timeline
Pregnancy is divided into three trimesters, each marking key developmental phases:
- First Trimester (Weeks 1 to 12): Fetal organogenesis and rapid initial development.
- Second Trimester (Weeks 13 to 26): Rapid skeletal growth and detectable movement.
- Third Trimester (Weeks 27 to 40+): Final maturation of lungs, weight gain, and preparation for birth.
Frequently Asked Questions
Only about 4% of babies are born on their exact due date. Most are born within a week before or after the EDD.
Yes, early ultrasound measurements (dating scans) during the first trimester are the most accurate way to establish a due date and may override LMP calculations.
If your cycles are highly irregular or you don't recall the date, your obstetrician will determine your gestational age using an early ultrasound scan.