Due Date of Baby Calculator

Pregnancy due dates are typically calculated based on the first day of the last menstrual period (LMP) or the date of a confirmed ultrasound. This calculator helps you estimate your baby's due date using either method.

How to Use This Calculator

To calculate your estimated due date:

Select whether you want to calculate based on your last menstrual period (LMP) or an ultrasound date.
Enter the relevant date in the provided field.
Click "Calculate" to see your estimated due date.

The calculator will display your estimated due date, the number of weeks until delivery, and a visual timeline of your pregnancy.

How the Due Date is Calculated

Pregnancy is typically considered to be 40 weeks long, with the due date calculated as follows:

Formula for LMP Method

Due Date = Last Menstrual Period + 280 days (40 weeks)

This is based on the average length of a menstrual cycle (28 days) multiplied by 10 cycles (280 days).

Formula for Ultrasound Method

Due Date = Ultrasound Date + (40 weeks - Gestational Age)

For example, if your ultrasound shows your baby is 12 weeks old, you would add 28 weeks (40 - 12) to the ultrasound date.

Note that these calculations are estimates. Actual delivery dates can vary by several days or more.

Example Calculation

Let's say you had your last menstrual period on January 1, 2024. Using the LMP method:

Start with January 1, 2024
Add 280 days (40 weeks)
Result: October 28, 2024

This would be your estimated due date using the LMP method.

Remember that pregnancy lengths can vary. Some babies arrive early, while others may come later than expected.

Frequently Asked Questions

Which method is more accurate for calculating due date?

The ultrasound method is generally more accurate because it provides an actual gestational age, while the LMP method relies on average cycle lengths which can vary.

Can my due date change after an ultrasound?

Yes, if your ultrasound shows a different gestational age than previously estimated, your due date may change. This is why many doctors recommend waiting until after 12 weeks for a more accurate ultrasound.

What if I don't remember my last menstrual period?

If you don't remember your LMP, you can use the ultrasound method once you have that information. Some doctors may also use other methods like counting fetal heartbeats or measuring cervical length.