Estimate your baby's due date and current week of pregnancy based on your last menstrual period.
Enter the first day of your last menstrual period (LMP) using the date picker.
Click "Calculate" to see your estimated due date, how many weeks pregnant you are, and your current trimester.
This calculation assumes a standard 28-day menstrual cycle. Consult your healthcare provider for a more precise estimate.
The estimated due date is calculated using Naegele's rule:
Due Date = Last Period Date + 280 days (40 weeks)
Trimesters: First trimester is weeks 1–12, second trimester is weeks 13–26, third trimester is weeks 27–40.
Example: Last menstrual period started on January 1, 2026.
Only about 5% of babies are born on their exact due date. Most births occur within two weeks before or after the estimated date. An ultrasound in the first trimester can provide a more accurate estimate.
Naegele's rule assumes a 28-day cycle. If your cycle is longer or shorter, your ovulation date shifts accordingly, which can change the due date by several days. Discuss this with your doctor.
The first trimester covers weeks 1 through 12, the second trimester covers weeks 13 through 26, and the third trimester covers weeks 27 through 40.