Delivery Baby Date Calculator

Pregnancy due dates are estimates based on the first day of your last menstrual period (LMP) or ultrasound date. This calculator helps you determine your estimated due date using standard pregnancy duration of 40 weeks.

How to Use This Calculator

To calculate your estimated due date:

Select whether you want to use your last menstrual period (LMP) or ultrasound date
Enter the date (LMP or ultrasound date)
Click "Calculate" to see your estimated due date

The calculator will display your estimated due date, the number of weeks and days until then, and a chart showing your pregnancy timeline.

How the Due Date Calculation Works

Pregnancy is typically considered to be 40 weeks long, from the first day of your last menstrual period (LMP) to the estimated due date.

Due Date = LMP Date + 40 weeks or Due Date = Ultrasound Date + (40 weeks - Ultrasound Weeks)

For example, if your LMP was January 1, 2023, your estimated due date would be January 2, 2024 (40 weeks later).

Ultrasound dates provide more accurate estimates because they account for the exact gestational age at the time of the scan.

Examples of Due Date Calculations

Example 1: Using Last Menstrual Period

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

Estimated due date: March 17, 2024 (40 weeks later)
Weeks until due date: 40 weeks

Example 2: Using Ultrasound Date

If you had an ultrasound on February 1, 2023 and were 12 weeks pregnant:

Estimated due date: February 3, 2024 (12 weeks + 28 weeks remaining)
Weeks until due date: 28 weeks

How Accurate Are Due Dates?

Due dates are estimates because pregnancy lengths can vary. About 90% of pregnancies fall within 38-42 weeks, with the average being 39-40 weeks.

For most people, the due date is accurate within about 1-2 weeks. However, it's always best to consult with your healthcare provider for the most accurate information.

Factors that can affect due date accuracy include:

Irregular menstrual cycles
Previous pregnancies with different lengths
Multiple pregnancies
High-risk conditions

Frequently Asked Questions

How is the due date calculated?

The due date is calculated by adding 40 weeks to the first day of your last menstrual period (LMP) or by adding the remaining weeks to your ultrasound date.

Is the due date always accurate?

No, due dates are estimates. About 90% of pregnancies fall within 38-42 weeks, with the average being 39-40 weeks. Ultrasound dates are more accurate.

What if I had an early ultrasound?

If you had an early ultrasound, you can use the calculator to determine your due date based on your gestational age at that time.

Can due dates change during pregnancy?

Yes, due dates can change if your healthcare provider discovers complications that may affect your pregnancy length.

What if I don't know my LMP date?

You can use an ultrasound date for a more accurate estimate. If you don't have either, consult with your healthcare provider.