Gestational Age Calculator

Gestational age is calculated from the first day of your last menstrual period (LMP), not from the date of conception. This is the standard method used by healthcare providers worldwide. Even though conception typically occurs about 2 weeks after your LMP (during ovulation), pregnancy is measured from the LMP because it's easier to track. A full-term pregnancy is 40 weeks (280 days) from the LMP, or 38 weeks from conception. The calculation is: gestational age = (current date - LMP date) converted to weeks and days.

Gestational age and fetal age differ by approximately 2 weeks. Gestational age is measured from the first day of your last menstrual period (LMP) and is the standard used by doctors and in pregnancy literature. Fetal age (also called embryonic age or conceptional age) is measured from the actual date of conception, which typically occurs about 14 days after the LMP during ovulation. For example, at "8 weeks pregnant" (gestational age), the fetus is actually about 6 weeks old (fetal age). Medical professionals use gestational age because LMP is more reliably known than the exact conception date.

Gestational age calculation based on LMP is accurate within 3-5 days if you have regular 28-day menstrual cycles and know your LMP date precisely. However, accuracy decreases if you have irregular cycles, can't remember your exact LMP, or ovulated earlier or later than day 14. The most accurate method for determining gestational age is an ultrasound performed in the first trimester (before 13 weeks), which can date pregnancy within 5-7 days. Healthcare providers often use a combination of LMP dating and early ultrasound measurements to determine the most accurate due date and gestational age.

Pregnancy is divided into three trimesters: First Trimester (Weeks 1-13): The embryo implants, major organs form, and the risk of miscarriage is highest. Common symptoms include morning sickness, fatigue, and breast tenderness. Second Trimester (Weeks 14-26): Often called the "honeymoon period" - energy returns, you start showing, and you can feel the baby move (quickening around 16-20 weeks). Anatomy scans are performed around week 20. Third Trimester (Weeks 27-40+): Baby gains weight rapidly, you may experience back pain and frequent urination, and the body prepares for labor. Full term is 37-42 weeks. Each trimester brings different developmental milestones and physical changes for both mother and baby.