Question 1

How is the pregnancy due date calculated?

Accepted Answer

Naegele and his rule adds 280 days (40 weeks) to the first day of your last menstrual period (LMP), or 266 days (38 weeks) to the conception date if known. The assumption is a 28-day cycle with ovulation at day 14, which may differ from your actual cycle.

Question 2

How accurate is the due date calculation?

Accepted Answer

Only about 4% of babies arrive on their actual due date. Healthy births generally happen within a 2-week window on either side. Your doctor may adjust the date based on ultrasound and can be more accurate, especially first-trimester dating scans.

Question 3

What if my cycle is not 28 days?

Accepted Answer

You can estimate by adding items to your LMP if cycles are longer, or subtracting if they are shorter. For example, a 32-day cycle with LMP adding the same four additional days beyond the 28-day default. This calculator shows the default estimate and allows subtle adjustment.

Question 4

Can I calculate from conception date?

Accepted Answer

Yes. If you tracked ovulation or had a fertility treatment date, you can calculate from that date by adding 266 days (38 weeks) for a due date. This is usually more accurate than LMP for those who can pinpoint the date.

Question 5

What happens with the calculator when I get to each trimester?

Accepted Answer

The calculator also shows the approximate start of each trimester. The first trimester spans weeks 1-13, the second weeks 14-27, and the third weeks 28 until birth. These milestones help with planning and prenatal care.

Pregnancy Due Date Calculator

How to Use the Pregnancy Due Date Calculator

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