wellnessMarch 1, 2026

دليل الحمل: فهم موعد الولادة المتوقع

Finding out you're pregnant is an exciting moment, and one of the first questions is 'When is my baby due?' Due date calculation is based on well-established medical formulas but understanding the nuances helps set realistic expectations about your delivery date.

How Due Dates Are Calculated

The most common method is 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. For example, if your LMP was January 1, your estimated due date would be October 8. If your cycles are longer or shorter than 28 days, the calculation adjusts accordingly.

Different Methods of Due Date Calculation

LMP-based calculation (Naegele's Rule) is the most common. Ultrasound dating, especially in the first trimester (most accurate before 13 weeks), measures the embryo's crown-rump length to estimate gestational age. Conception date calculation adds 266 days from known conception. IVF patients have the most precise dating based on embryo transfer date. When LMP and ultrasound dates differ by more than 7 days, the ultrasound date is typically used.

How Accurate Are Due Dates?

Only about 5% of babies are born on their exact due date. Most babies (80%) are born within 2 weeks of the due date, between 38-42 weeks. First babies tend to arrive slightly later than subsequent pregnancies. A full-term pregnancy ranges from 39-40 weeks, with 'early term' at 37-38 weeks and 'late term' at 41-42 weeks. Your due date is best thought of as an estimate rather than a precise prediction.

What to Expect: First Trimester (Weeks 1-12)

The first trimester is a period of rapid development. By week 4, the embryo implants in the uterine wall. By week 8, all major organs have begun forming. Common symptoms include morning sickness, fatigue, breast tenderness, and frequent urination. The first prenatal visit typically occurs around week 8-10, including blood work, medical history review, and often the first ultrasound.

What to Expect: Second Trimester (Weeks 13-26)

Often called the 'golden period' of pregnancy, many women feel their best during the second trimester as morning sickness subsides and energy returns. You'll likely feel the baby's first movements (quickening) between weeks 16-25. The anatomy scan ultrasound around week 20 checks the baby's growth and development. You may start showing and may learn the baby's sex if desired.

What to Expect: Third Trimester (Weeks 27-40)

The baby grows rapidly in the third trimester, gaining about half a pound per week. Common symptoms include back pain, heartburn, Braxton Hicks contractions, and difficulty sleeping. Prenatal visits become more frequent (every 2 weeks, then weekly). The baby typically moves into a head-down position by week 36. Pack your hospital bag by week 36 and familiarize yourself with signs of labor.

Calculate Your Due Date

Use our free Pregnancy Due Date Calculator to find your estimated delivery date and track your pregnancy milestones.

Try Pregnancy Calculator

Frequently Asked Questions

How many weeks is a full-term pregnancy?

A full-term pregnancy is 39-40 weeks (measured from the first day of the last menstrual period). Early term is 37-38 weeks, late term is 41 weeks, and post-term is 42+ weeks. Babies born at 39+ weeks generally have better health outcomes.

Can my due date change?

Yes, your due date may be adjusted based on ultrasound measurements, especially if the first-trimester ultrasound differs from the LMP-based estimate by more than 7 days. The ultrasound date is generally considered more accurate, particularly in early pregnancy.

What if I don't know my last period date?

If you don't know your LMP, an early ultrasound (ideally before 13 weeks) can accurately estimate your due date by measuring the embryo's size. Your healthcare provider can also use other clinical indicators to estimate gestational age.