Pregnancy Due Date Calculator

How to Use the Pregnancy Due Date Calculator

The Pregnancy Due Date Calculator estimates your expected delivery date based on your last menstrual period (LMP) or known conception date. It also shows your current week of pregnancy, trimester, and key developmental milestones throughout the 40-week journey.

Calculation Methods

From Last Menstrual Period: Enter the first day of your last period. The calculator uses Naegele rule: add 7 days and subtract 3 months (or equivalently, add 280 days). If your LMP was January 1, your estimated due date is October 8.

From Conception Date: If you know when conception occurred, the calculator adds 266 days (38 weeks) to that date. Conception typically occurs about 14 days after the first day of the last period in a 28-day cycle.

Understanding the Timeline

First Trimester (Weeks 1-12): Major organs begin forming. Early pregnancy symptoms include fatigue, nausea, and breast tenderness. The first ultrasound typically occurs around weeks 8-12.

Second Trimester (Weeks 13-26): Often called the golden period. Energy returns, and you may feel the baby move around week 18-22. The anatomy scan occurs around week 20.

Third Trimester (Weeks 27-40): The baby grows rapidly, gaining about half a pound per week. Prepare for delivery during this period. Most babies are born between weeks 39 and 41.

Due Date Accuracy

Only about 5% of babies arrive on their exact due date. The estimated due date represents the midpoint of a normal delivery window. Full-term delivery ranges from 37 to 42 weeks. Most first-time mothers deliver slightly past their due date. Your healthcare provider may adjust the date based on ultrasound measurements.

Frequently Asked Questions

Q: How accurate is the due date calculation?

A: The calculation assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, the estimate may be off by a few days. An early ultrasound (before 12 weeks) can refine the due date to within 5-7 days of accuracy.

Q: What if I do not remember my last period date?

A: If you are unsure of your LMP, an early ultrasound can estimate gestational age by measuring the embryo. This dating ultrasound is most accurate during the first trimester. Discuss timing with your healthcare provider.

Q: Can my due date change?

A: Yes. If early ultrasound measurements differ from the LMP-based date by more than 7 days, your provider may adjust the due date. The ultrasound-based estimate is generally more reliable, especially for women with irregular cycles.