Calculate Baby's Due Date

Calculating your baby's due date is an important part of pregnancy planning. This calculator helps you determine your estimated due date based on your last menstrual period or ultrasound date. Understanding how pregnancy weeks work can help you track your pregnancy progress accurately.

How to Use This Calculator

Using our baby due date calculator is simple. You can calculate your due date in two ways:

By entering your last menstrual period (LMP) date
By entering your ultrasound date and the number of weeks at that time

For the most accurate results, use the ultrasound method if you've had an ultrasound. If you don't have an ultrasound date, the LMP method is still useful for estimating your due date.

Note: The average pregnancy lasts 40 weeks (280 days). However, due dates can vary by about 2 weeks before and after the calculated date.

How Pregnancy Due Dates Are Calculated

The due date calculation is based on the average length of a full-term pregnancy, which is 40 weeks (280 days) from the first day of the last menstrual period. Here's how the calculation works:

Formula

For LMP method:

Due Date = LMP Date + 280 days

For ultrasound method:

Due Date = Ultrasound Date + (40 - Ultrasound Weeks) × 7 days

For example, if you had your last menstrual period on January 1, 2023, your due date would be around October 28, 2023. If you had an ultrasound at 12 weeks, your due date would be around October 28, 2023 (12 weeks + 28 weeks = 40 weeks).

It's important to remember that due dates are estimates. Some babies arrive early, and others arrive late. The due date is based on the average length of pregnancy, not an exact science.

Examples of Due Date Calculations

Let's look at a couple of examples to see how the due date calculation works in practice.

Example 1: Using Last Menstrual Period

If your last menstrual period started on March 15, 2023, your due date would be calculated as follows:

March 15, 2023 + 280 days = October 11, 2023

So, your estimated due date would be around October 11, 2023.

Example 2: Using Ultrasound Date

If you had an ultrasound on April 1, 2023, and it showed your baby was 14 weeks old, your due date would be calculated as follows:

April 1, 2023 + (40 - 14) weeks = April 1, 2023 + 26 weeks = October 4, 2023

So, your estimated due date would be around October 4, 2023.

Remember, these are estimates. Your actual due date may vary by a week or two.

Frequently Asked Questions

How accurate is the due date calculation?

The due date calculation is based on the average length of pregnancy, which is 40 weeks. However, due dates can vary by about 2 weeks before and after the calculated date. For the most accurate results, use the ultrasound method if you've had an ultrasound.

Can I use this calculator if I'm pregnant with twins or multiples?

This calculator is designed for singleton pregnancies. If you're pregnant with twins or multiples, your due date may be different. It's best to consult with your healthcare provider for the most accurate information.

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

If you don't know your last menstrual period date, you can use the ultrasound method if you've had an ultrasound. If you haven't had an ultrasound, you can estimate your due date based on your menstrual cycle length.

Is the due date the same as the expected delivery date?

Yes, the due date and expected delivery date are essentially the same thing. They refer to the estimated date when your baby is expected to be born.