Calculate Baby Delivery Due Date

Calculating your baby's due date is an important step in pregnancy planning. There are several methods to determine your estimated due date (EDD), each with its own assumptions and accuracy levels. This guide explains the most common methods and how to use our calculator to estimate your delivery date.

How to Calculate Due Date

The most common method for calculating due date is the Last Menstrual Period (LMP) method. This method assumes a standard 280-day pregnancy (40 weeks).

Due Date = Last Menstrual Period + 280 days

For example, if your last period started on January 1, your due date would be October 31 (280 days later).

Other Methods

If you know your conception date or have had an ultrasound, you can use these alternative methods:

Due Date = Conception Date + 280 days Due Date = Ultrasound Date + (280 - Gestational Age in Days)

Ultrasound dates are generally more accurate than LMP dates because they account for variations in menstrual cycle length.

Different Methods for Due Date

There are three primary methods to calculate due date:

Last Menstrual Period (LMP): The most common method, assuming a 280-day pregnancy.
Conception Date: More accurate if you know when you conceived.
Ultrasound Date: Most accurate, using the date of the ultrasound and the gestational age.

Note: Due dates calculated by any method are estimates. Actual delivery dates can vary by several weeks.

Worked Example

Let's calculate a due date using the LMP method:

If your last menstrual period started on March 15, 2023:

Due Date = March 15, 2023 + 280 days Due Date = December 12, 2023

Your estimated due date would be December 12, 2023.

Frequently Asked Questions

How accurate is the due date calculation?

Due date calculations are estimates. The actual delivery date can vary by several weeks. Ultrasound dates are generally more accurate than LMP dates.

What if my menstrual cycle is irregular?

If your cycle is irregular, the LMP method may be less accurate. In this case, using the conception date or an ultrasound date is recommended.

Can I calculate due date before conception?

No, you need either your last menstrual period date, conception date, or ultrasound information to calculate a due date.

What if I have twins or multiples?

The due date calculation remains the same for multiples. The due date is typically calculated from the first day of the mother's last menstrual period.