Baby Center Pregnancy Due Date Calculator

Calculating your pregnancy due date is essential for tracking your pregnancy timeline. This calculator helps you determine your estimated delivery date based on your last menstrual period (LMP) or ultrasound date.

How to Use This Calculator

To calculate your pregnancy due date:

Enter the date of your last menstrual period (LMP) or the date of your first trimester ultrasound.
Select whether you're using the LMP method or the ultrasound method.
Click "Calculate" to see your estimated due date.

The calculator will display your estimated due date and provide additional information about your pregnancy timeline.

How Pregnancy Due Date is Calculated

There are two main methods for calculating a pregnancy due date:

Last Menstrual Period (LMP) Method

The LMP method estimates the due date by adding 280 days (40 weeks) to the first day of your last menstrual period.

Due Date = LMP Date + 280 days

Ultrasound Method

The ultrasound method uses the gestational age from an ultrasound to calculate the due date. The formula varies slightly depending on whether the ultrasound was performed in the first or second trimester.

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

Note: The LMP method is generally less accurate than the ultrasound method, especially in the first trimester. Ultrasound dates are considered more reliable.

Understanding the Pregnancy Timeline

A typical pregnancy lasts about 40 weeks (280 days) from the first day of your last menstrual period. Here's a general breakdown of the pregnancy timeline:

Week	Development Stage
1-4	Implantation and early development
5-8	Organ formation begins
9-12	Fetal movement and facial features develop
13-16	Limbs and fingers develop
17-20	Eyes, ears, and hair begin to form
21-24	Brain development accelerates
25-28	Lungs and liver begin to function
29-40	Growth and preparation for birth

Your healthcare provider may adjust your due date based on your individual pregnancy.

Common Questions About Due Dates

Here are answers to some frequently asked questions about pregnancy due dates:

Why do due dates change?

Due dates can change based on your individual pregnancy. Factors like your menstrual cycle length, ultrasound results, and your healthcare provider's assessment can all influence the due date.

Is the LMP method accurate?

The LMP method is generally accurate within about 10 days, but it can be less precise in the first trimester. Ultrasound dates are considered more reliable.

What if my due date changes?

If your due date changes, it's important to discuss this with your healthcare provider. They can provide guidance on what this means for your pregnancy and delivery plans.

Can I trust my due date?

While due dates are helpful for planning, they're estimates. Your healthcare provider will monitor your pregnancy closely and adjust your due date as needed.