Baby Born Calculation Date

Determining the baby's born date is essential for tracking development milestones, scheduling doctor visits, and planning for the baby's arrival. Our calculator helps you calculate the expected due date or baby born date based on your last menstrual period (LMP) or ultrasound date.

How to Calculate Baby Born Date

There are two primary methods to calculate the baby's born date:

Last Menstrual Period (LMP) Method: This is the most common method. The average pregnancy lasts 40 weeks (280 days), so you can add 280 days to your LMP date to estimate the due date.
Ultrasound Date Method: If you had an ultrasound, the healthcare provider will calculate the due date based on the baby's gestational age at the time of the scan.

The calculator below uses the LMP method to estimate the due date. Simply enter your last menstrual period date, and it will calculate the expected due date.

Formula Used

Due Date = Last Menstrual Period (LMP) + 280 days

This formula is based on the average length of a full-term pregnancy, which is 40 weeks (280 days). The due date is calculated by adding 280 days to the first day of your last menstrual period.

For example, if your last menstrual period started on January 1, 2023, your due date would be:

January 1, 2023 + 280 days = October 7, 2023

Worked Examples

Example 1: Calculating Due Date from LMP

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

March 15, 2023 + 280 days = December 10, 2023

Example 2: Calculating Due Date from Ultrasound

If you had an ultrasound at 12 weeks and 3 days, the due date would be:

Ultrasound date + (40 weeks - 12 weeks - 3 days) = Due date

This method is more precise but requires the healthcare provider's calculation.

Frequently Asked Questions

How accurate is the due date calculation?: The due date calculated from the LMP method is an estimate. The actual due date can vary by several days. Ultrasound dates are more precise but require medical confirmation.
Can the due date change after the first trimester?: Yes, the due date can change if the baby's growth rate is different from the average. Ultrasounds in the second and third trimesters provide more accurate due dates.
What if I don't know my LMP date?: If you don't know your LMP date, you can estimate it by counting back 280 days from your due date or using an ultrasound date.