Question 1

How is my due date calculated?

Accepted Answer

The most common method, Naegele's rule, adds 280 days (40 weeks) to the first day of your last menstrual period, assuming a 28-day cycle with ovulation on day 14.

Question 2

How accurate is a pregnancy due date calculator?

Accepted Answer

Due date calculators provide an estimate rather than a guarantee — only about 5% of babies are born on their exact due date, though most arrive within about two weeks before or after.

Question 3

How do I calculate my due date with irregular periods?

Accepted Answer

With irregular cycles, adjusting the calculation for your average cycle length, or dating the pregnancy by an early ultrasound instead of LMP, generally gives a more reliable estimate.

Question 4

How is an IVF due date calculated for a day 5 transfer?

Accepted Answer

For a day 5 blastocyst transfer, the due date is typically the transfer date plus 261 days, since the embryo is already 5 days past fertilization at the time of transfer.

Question 5

How is an IVF due date calculated for a day 3 transfer?

Accepted Answer

For a day 3 embryo transfer, the due date is typically the transfer date plus 263 days, accounting for the embryo being 3 days past fertilization at transfer.

Question 6

How is due date calculated from an ultrasound?

Accepted Answer

An ultrasound estimates gestational age from fetal measurements, and the due date is calculated by adding the remaining days to reach 280 days total gestation from that scan date.

Question 7

What is the difference between gestational age and fetal age?

Accepted Answer

Gestational age is counted from the first day of the last menstrual period, while fetal (conceptional) age is counted from the estimated date of conception, typically about 2 weeks less than gestational age.

Question 8

When does the first trimester end?

Accepted Answer

The first trimester typically ends at the end of week 13 of gestational age, after which the second trimester begins.

Question 9

When does the second trimester start and end?

Accepted Answer

The second trimester generally spans weeks 14 through 27 of gestational age.

Question 10

When does the third trimester start?

Accepted Answer

The third trimester generally begins at week 28 of gestational age and continues until birth, around week 40.

Question 11

Can my due date change during pregnancy?

Accepted Answer

Yes. An early ultrasound is often considered more accurate than LMP-based dating and can shift the estimated due date, especially if cycles were irregular or LMP was uncertain.

Question 12

How accurate is Naegele's rule?

Accepted Answer

Naegele's rule assumes a standard 28-day cycle with ovulation on day 14, so it becomes less accurate for people with longer, shorter, or irregular cycles.

Question 13

What is considered full term for a pregnancy?

Accepted Answer

Full term is generally defined as 39 weeks 0 days through 40 weeks 6 days of gestation, with early term, late term, and post-term as separate categories on either side.

Question 14

What are the key prenatal appointments and screenings during pregnancy?

Accepted Answer

Common milestones include first trimester screening around weeks 11-13, the anatomy ultrasound around weeks 18-22, glucose screening around weeks 24-28, and Group B strep testing around weeks 35-37.

Question 15

How many weeks pregnant am I?

Accepted Answer

Your current gestational age is calculated as the number of days since your estimated last menstrual period, divided into completed weeks and remaining days.

Question 16

Is it normal to deliver before or after the due date?

Accepted Answer

Yes. Due dates are statistical estimates, and it's entirely normal for labor to begin anytime from about three weeks before to two weeks after the estimated due date.

Trimester	Gestational Weeks
First Trimester	Weeks 1-13
Second Trimester	Weeks 14-27
Third Trimester	Weeks 28-40

Milestone	Typical Timing
First Trimester Screening	Weeks 11-13
Anatomy Ultrasound	Weeks 18-22
Glucose Screening	Weeks 24-28
Third Trimester Begins	Week 28
Group B Strep Test	Weeks 35-37
Full Term	Weeks 39-41

Pregnancy Due Date Calculator (2026)

How Due Dates Are Calculated (4 Methods)

Last Menstrual Period (Naegele's Rule)

Conception Date

IVF Embryo Transfer

Ultrasound Dating

Pregnancy Trimesters by Week

Prenatal Appointment & Screening Schedule

How Accurate Is a Due Date Calculator?

Related Calculators

Scientific References

Pregnancy Due Date Calculator — Frequently Asked Questions