Delivery Date of Baby Calculator

Pregnancy is a journey, and knowing your estimated due date is an important first step. Our delivery date of baby calculator helps you determine when you might expect your baby to arrive based on your last menstrual period or ultrasound date.

How to Use This Calculator

To calculate your estimated due date, you'll need either:

Your last menstrual period (LMP) date, or
An ultrasound date and the number of weeks completed at that time

Enter the relevant information in the calculator on the right, then click "Calculate" to see your estimated due date.

Important Note

This calculator provides an estimate. Actual delivery dates can vary by several days from the calculated date. Always consult with your healthcare provider for personalized advice.

How the Due Date is Calculated

The standard pregnancy length is considered to be 40 weeks (280 days) from the first day of the last menstrual period. The due date is calculated by adding 40 weeks to the first day of your last menstrual period.

Formula Used

Estimated Due Date = Last Menstrual Period + 40 weeks

Or for ultrasound dates:

Estimated Due Date = Ultrasound Date + (40 - Completed Weeks) weeks

For example, if your last menstrual period started on January 1, 2023, your estimated due date would be October 31, 2023. If you had an ultrasound at 12 weeks, your due date would be calculated as the ultrasound date plus 28 weeks.

How Accurate is the Due Date?

Estimated due dates are generally accurate within about 10 days, but actual delivery dates can vary. Factors that can affect the due date include:

Irregular menstrual cycles
Early or late ovulation
Fertilization timing
Embryo development rate
Placental development

Ultrasound dates are more accurate than LMP-based estimates, typically within 3-5 days of the actual delivery date.

Method	Typical Accuracy	Best For
Last Menstrual Period (LMP)	±10 days	Early pregnancy (before 12 weeks)
Ultrasound Date	±3-5 days	After 12 weeks of pregnancy

Common Questions About Due Dates

Here are some frequently asked questions about pregnancy due dates:

FAQ

Can my due date change?

Yes, your due date can change based on new information from ultrasounds or other medical assessments. Always follow your healthcare provider's guidance.

What if I'm pregnant with twins or multiples?

The due date calculation remains the same for multiple pregnancies. Each baby will typically be born within a few days of each other.

How do I know if my due date is accurate?

Regular prenatal checkups and ultrasounds can help confirm your due date. Your healthcare provider will monitor your pregnancy progress.

What if I miss my period and think I'm pregnant?

A missed period can indicate pregnancy, but it's important to confirm with a home pregnancy test or medical professional. Early symptoms may include fatigue, nausea, and breast tenderness.