How is Your Due Date Calculated?
Standard pregnancy calculations are based on the first day of your Last Menstrual Period (LMP). Clinically, a typical pregnancy lasts approximately 40 weeks (280 days) from LMP. We calculate your due date using Naegele's Rule, which adds 280 days to the LMP and adjusts for your average menstrual cycle length. If your cycle is longer or shorter than the standard 28-day cycle, the ovulation timing offset is automatically adjusted.
Understanding the Trimesters of Pregnancy
A pregnancy is divided into three distinct segments called trimesters, marked by different physiological milestones:
First Trimester
Weeks 1 - 13Organogenesis begins. The baby's heart, brain, spinal cord, and limbs form. Hormonal fluctuations are highest, and risk of miscarriage drops after week 13.
Second Trimester
Weeks 14 - 27Often called the "golden phase" as morning sickness fades. The baby begins to hear sounds, swallow amniotic fluid, and develop sleep-wake cycles.
Third Trimester
Weeks 28 - 40+Rapid fetal weight gain occurs. The baby's lungs prepare for breathing, bones strengthen, and head-down positioning starts for delivery.
Important Milestones to Note
While a full term is defined as 37 weeks or more, baby survival viability threshold typically begins around Week 24, as the lungs produce surfactant to survive external breathing. Keep in mind that only 4% of babies are born exactly on their due date—the estimate serves as a helpful baseline for medical preparation.