Question 1

How is my due date calculated?

Accepted Answer

Your due date is calculated using 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. Our Due Date Calculator also supports conception date and ultrasound-based dating for more precision.

Question 2

How do I count pregnancy weeks?

Accepted Answer

Pregnancy weeks are counted from the first day of your last menstrual period (LMP), not from conception. Week 1 begins on the day your period starts, even though you are not yet pregnant at that point. Conception typically occurs in week 2. Our Pregnancy Week Calculator tells you your exact gestational age today.

Question 3

What are the three trimesters of pregnancy?

Accepted Answer

The first trimester spans weeks 1–13 and covers the period of most rapid organ formation. The second trimester covers weeks 14–27, when the fetus grows rapidly and many parents receive the anatomy scan. The third trimester runs from week 28 to birth (typically week 40), when the baby gains most of its weight.

Question 4

How does IVF dating differ from natural conception dating?

Accepted Answer

For IVF pregnancies, the due date is calculated from the embryo transfer date, not the LMP. The formula is: add 266 days (38 weeks) to the transfer date, then subtract the embryo's age in days (3 days for Day 3, 5 days for Day 5). Our Due Date Calculator includes an IVF transfer mode that handles this automatically.

Question 5

Can my due date change during pregnancy?

Accepted Answer

Yes. Early ultrasound dating (typically at 8–12 weeks) is more accurate than LMP-based dating because embryo size varies less than cycle length at that stage. If the ultrasound date differs from the LMP date by more than 5–7 days in the first trimester, most providers will adjust your due date. Later ultrasounds are less reliable for re-dating because normal growth variation increases. Our Ultrasound Due Date Calculator lets you compare both methods.

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How Due Dates Are Calculated (And Why They Change)

Your Pregnancy Week by Week: What to Expect

IVF Due Date Calculations Explained

Understanding Trimester Milestones

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