Due Date Calculator

Estimate Based On:

First Day of Your Last Period: Average Length of Your Cycles (days):

Ultrasound Date: Gestational Age at Ultrasound (weeks & days):

weeks days

Conception Date:

IVF Transfer Date: Embryo Age:

Due Date Calculator

The Due Date Calculator helps estimate when a pregnant woman is likely to deliver. The calculation can be based on the last menstrual period (LMP), an ultrasound scan, the conception date, or the date of an IVF embryo transfer.

Understanding the Estimated Due Date

The due date (also called the estimated date of confinement) is the projected day a woman may give birth. Instead of viewing it as a fixed date, it is better to consider it a timeframe—because only about 4% of babies are born on their exact due date.

Healthcare providers use several methods to calculate the due date, including the LMP, ultrasound results, conception date, and IVF transfer date.

Methods of Estimating Due Date

1. Last Menstrual Period (LMP)

The most common way to estimate a due date is by starting with the first day of the last menstrual period. Pregnancy is generally assumed to last 280 days (40 weeks) from that date. While some debate exists about whether pregnancy begins at fertilization or implantation, gestational age is always measured from the LMP for consistency. In practice, most pregnancies last between 37 and 42 weeks, with 40 weeks being the standard estimate. So, the due date is usually calculated by adding 40 weeks to the first day of the LMP.

2. Ultrasound

An ultrasound scan uses sound waves to check the baby’s growth inside the womb. By comparing fetal size to average growth patterns, doctors can estimate how far along the pregnancy is. Ultrasounds are safe, quick, and effective, and are especially reliable for estimating due dates during the early weeks of pregnancy.

3. Conception Date

If the conception date is known, it can also be used to estimate the due date. Since ovulation and conception typically occur about two weeks after the LMP, this method usually produces a date roughly two weeks later than the LMP-based calculation.

4. In Vitro Fertilization (IVF)

For women who undergo IVF, the due date is often more precise, because the exact timing of embryo transfer is known. The standard calculation still assumes an average pregnancy length of 40 weeks from LMP, but with IVF, doctors can use the egg retrieval date, fertilization date, ovulation day, or the 3-day/5-day embryo transfer date for greater accuracy. In most calculators, the embryo transfer date serves as the main reference point.

Due Date as a Medical Guide

Babies can be born at different points within the 37–42 week window, and most outcomes are normal. These stages are classified as:

Early term: 37–39 weeks
Full term: 39–41 weeks
Late term: 41–42 weeks

While full-term babies generally have the best health outcomes, early-term and late-term births are often safe as well.

Babies born before 37 weeks are considered preterm (premature), which can lead to complications due to underdeveloped organs.
e="font-weight: 400;" aria-level="1">Babies born after 42 weeks are considered postterm. At this stage, the placenta may weaken, reducing the supply of oxygen and nutrients, while the baby continues to grow. If this happens, doctors may recommend inducing labor.

In summary:
The Due Date Calculator provides an estimated delivery timeline, not an exact prediction. Whether based on LMP, ultrasound, conception, or IVF transfer, it serves as a guideline for monitoring pregnancy progress and ensuring the baby’s health.