Enter your due date or last menstrual period to see your current week, baby's size, and key developments.
Pregnancy dating starts from the first day of your last menstrual period (LMP), not from the date of conception. This means you're technically considered "pregnant" about 2 weeks before conception actually occurs. It's confusing, but it's the universal standard used by OB-GYNs because LMP is a more reliable date than ovulation or conception, which are harder to pinpoint.
A full-term pregnancy is 40 weeks (280 days) from LMP. Most babies are born between 38 and 42 weeks. Only about 5% arrive on their actual due date. Due dates calculated from LMP are estimates, not appointments.
First trimester (weeks 1-12): All major organs form during this period. The risk of miscarriage is highest in the first trimester and drops significantly after week 12. Morning sickness, fatigue, and breast tenderness are common symptoms. The baby goes from a cluster of cells to a recognizable human form about 2 inches long.
Second trimester (weeks 13-27): Often called the "honeymoon trimester" because many first-trimester symptoms ease up. You'll likely feel the first kicks (quickening) between weeks 16-22. The anatomy scan around week 20 checks for structural abnormalities and can reveal the baby's sex. The baby grows from about 3 inches to 14 inches.
Third trimester (weeks 28-40): The baby gains most of its weight during this period, growing from about 2.5 pounds to an average of 7.5 pounds at birth. Lung development is the final major milestone. Braxton Hicks contractions (practice contractions) become common. The baby drops into the pelvis in preparation for delivery.
Week 24 is considered the threshold of viability, meaning a baby born at 24 weeks has a reasonable chance of survival with intensive neonatal care. Survival rates at 24 weeks are roughly 60-70% at major medical centers, rising to 90%+ by 28 weeks. Before 24 weeks, survival is possible but outcomes are more uncertain.
For related pregnancy tools, use our Due Date Calculator for a precise estimate, or the Pregnancy Weight Calculator to track healthy weight gain through each trimester.
Many women are surprised to learn that "week 1" of pregnancy is actually the week of their last period, before conception has even occurred. Ovulation typically happens around week 2, and implantation occurs around week 3-4. A positive home pregnancy test usually shows up around weeks 4-5, when you would have expected your period.
Your due date is an estimate based on a 40-week average, but healthy full-term pregnancies range from 37 to 42 weeks. First-time mothers tend to go slightly past their due date on average, while subsequent pregnancies are slightly more likely to arrive on time or early. Only about 5% of babies arrive on their exact due date. The due date gives you and your care team a target for monitoring development and planning care, not a deadline.
If your cycle is irregular or you conceived through IVF, your OB-GYN may adjust your due date based on an early ultrasound measurement, which is more accurate than LMP dating for determining gestational age.