When Baby Born Calculator

Determine when your baby was born using either the last menstrual period (LMP) or ultrasound date. This calculator provides an estimated due date and gestational age based on standard pregnancy duration.

How to Use This Calculator

To estimate when your baby was born:

Select whether you want to use the last menstrual period (LMP) or ultrasound date
Enter the relevant date (LMP or ultrasound date)
Click "Calculate" to see the estimated birth date and gestational age

The calculator uses standard pregnancy duration of 40 weeks (280 days) from conception to birth. For most healthy pregnancies, this provides a good estimate.

Formula Used

The calculation is based on standard pregnancy duration:

Estimated Birth Date = Input Date + 280 days Gestational Age = Current Date - Input Date

Where:

Input Date is either the last menstrual period (LMP) or ultrasound date
280 days represents the average pregnancy duration

Note: This is an estimate. Actual birth dates can vary due to individual differences in pregnancy duration.

Worked Example

Example calculation using LMP:

If your last menstrual period was on January 1, 2023:

Estimated birth date: January 1, 2023 + 280 days = October 7, 2023
If today is October 1, 2023, gestational age: October 1, 2023 - January 1, 2023 = 9 months

This shows the baby is estimated to be born on October 7, 2023, and is currently 9 months pregnant.

Frequently Asked Questions

Q: Why are there two date options?

A: The last menstrual period (LMP) is the most common starting point, but some women may have an ultrasound date that provides a more precise estimate of when conception occurred.

Q: Is this calculation always accurate?

A: No, this is an estimate. Actual pregnancy durations can vary by several days or more. For precise timing, medical professionals use ultrasound measurements.

Q: What if I don't remember my LMP?

A: You can use the ultrasound date if you have one. If you don't have either, you can estimate based on your due date if you know it.