Pregnancy Calculator
Enter your values below and click Calculate for instant results.
days
Calculate your estimated due date from your last menstrual period. See trimester dates, gestational age, and conception date.
Enter your values below and click Calculate for instant results.
The standard method for calculating a due date is Naegele's rule: add 280 days (40 weeks) to the first day of the last menstrual period. This assumes a 28-day cycle with ovulation occurring on day 14. For cycles that differ from 28 days, the due date is adjusted accordingly. This calculator applies that adjustment automatically when you enter your cycle length.
Only about 5% of babies are born on their exact due date. Most births occur within two weeks before or after the estimated date. The due date is best understood as the middle of a likely delivery window rather than a specific deadline.
Pregnancy is divided into three trimesters, each roughly 13 weeks long. The first trimester (weeks 1 through 13) encompasses the most critical period of organ development. The second trimester (weeks 14 through 27) is often the most comfortable, with reduced nausea and more energy. The third trimester (weeks 28 through 40) involves the final growth and preparation for birth.
Gestational age, measured from the last menstrual period, is two weeks longer than fetal age, which is measured from the actual moment of conception. Healthcare providers use gestational age as the standard because it is based on the more precisely known LMP date rather than the often uncertain conception date. When a provider says the baby is 20 weeks, they mean 20 weeks from LMP, not 20 weeks from fertilization.
This calculator provides estimates for informational purposes. Ultrasound measurements during pregnancy are the most accurate method for confirming gestational age and due date. Always consult with a qualified healthcare provider for medical guidance during pregnancy.