Pregnancy Due Date Calculator

How to Use This Pregnancy Due Date Calculator

Calculate your estimated due date based on your last menstrual period (LMP), conception date, or IVF transfer date. See week-by-week milestones, trimester timeline, and important prenatal checkup dates.

1. Enter your values in the input fields provided.
2. The tool calculates results automatically as you type.
3. View detailed results and breakdowns below the calculator.
4. Copy or download results as needed.
5. All data stays in your browser — nothing is uploaded to any server.

How Due Dates Are Calculated

The most common method uses Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle with ovulation on day 14. If your cycles are longer or shorter, the due date may shift. Only about 5% of babies are born on their exact due date — most arrive within two weeks before or after.

Understanding Trimesters

Pregnancy is divided into three trimesters. The first trimester (weeks 1-12) involves rapid cell division and organ formation. The second trimester (weeks 13-27) is often considered the most comfortable, with visible growth and movement. The third trimester (weeks 28-40) involves final growth and preparation for birth.

Important Prenatal Milestones

Key milestones include: first heartbeat detection (week 6-7), first ultrasound (week 8-12), anatomy scan (week 18-22), glucose screening (week 24-28), Group B strep test (week 35-37), and full-term designation (week 39). Regular prenatal care is essential for monitoring both maternal and fetal health.

Factors That Affect Due Date Accuracy

Several factors can shift your actual delivery date: irregular menstrual cycles, the timing of ovulation (which varies from person to person), first-time vs subsequent pregnancies, the mother's age, and genetic factors. First-time mothers tend to deliver slightly later than the estimated date, while subsequent pregnancies may deliver earlier.