The pregnancy due date is the estimated date when a baby is expected to be born, usually 40 weeks (280 days) from the first day of the last menstrual period (LMP). However, only about 5% of babies are actually born on their exact due date—most arrive within 2 weeks before or after.

First day of period also called Naegele’s Rule

Take the first day of your last menstrual period (LMP). Add 7 days to the LMP.

Subtract 3 months (or add 9 months if calculating forward). Adjust the year if necessary.

Example:

LMP: May 1, 2024

Add 7 days → May 8, 2024

Subtract 3 months → February 8, 2025

Estimated Due Date: February 8, 2025

If you do happen to know precisely when you conceived, if you are using an ovulation predictor or tracking - you can calculate your pregnancy due date based on your conception date. Remeberoose that calculation method from the pulldown above and put in your date.

Remeber, you don’t necessarily conceive on the day you have sex.

First-trimester ultrasound (6–12 weeks) is the most reliable way to determine a due date.

Based on crown-rump length (CRL), it can confirm or adjust the estimated due date.

Example:

If an ultrasound at 8 weeks 2 days suggests a due date of March 17, 2025, doctors may adjust it even if your LMP suggests a different date.

For pregnancies conceived via IVF or IUI, the due date is calculated differently:

🔹 IVF Due Date Formula:

Embryo transfer date + 266 days (38 weeks)

If using a 5-day embryo, add 261 days instead.

Example:

IVF Transfer Date (5-day embryo) = July 1, 2024

Due date = March 19, 2025

Yes, doctors may adjust the due date based on:

Ultrasound scans (more accurate in early pregnancy)

Irregular periods or late ovulation

Baby’s growth measurements