How to Use This Pregnancy Calculator
Enter the first day of your last menstrual period (LMP) and your average cycle length. The calculator uses Naegele's rule adjusted for your cycle length to estimate your due date, current week of pregnancy, and key milestones throughout your pregnancy journey.
Understanding Your Due Date
Your estimated due date is calculated as 280 days (40 weeks) from the first day of your last menstrual period, adjusted for cycle length. Only about 5% of babies are born on their exact due date. Most births occur between weeks 38 and 42. Your healthcare provider may adjust your due date based on ultrasound measurements.
Trimester Overview
First Trimester (Weeks 1-13): Major organ development occurs. This is when morning sickness is
most common. The risk of miscarriage drops significantly after week 12.
Second Trimester (Weeks 14-27): Often called the "golden period" as energy returns and nausea
fades. You'll feel baby's first movements and have an anatomy scan around week 20.
Third Trimester (Weeks 28-40): Baby gains weight rapidly and prepares for birth. You may
experience more physical discomfort as the baby grows larger.
Cycle Length Adjustment
The standard calculation assumes a 28-day cycle. If your cycle is longer or shorter, the due date is adjusted accordingly. For example, a 35-day cycle adds 7 days to the estimated due date, since ovulation likely occurred later. This is important for accurate dating, especially in early pregnancy.
When to See a Doctor
Schedule your first prenatal appointment between weeks 6 and 8. Contact your healthcare provider immediately if you experience heavy bleeding, severe pain, or other concerning symptoms. This calculator provides estimates only and should not replace professional medical advice.