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When Will Baby Be Due Calculator

Reviewed by Calculator Editorial Team

Pregnancy due dates are estimated based on the first day of your last menstrual period (LMP) or ultrasound results. This calculator helps you determine your expected due date using standard medical guidelines.

How to Use This Calculator

To calculate your due date:

  1. Enter the first day of your last menstrual period (LMP) in the date field.
  2. If you have an ultrasound date, select "Ultrasound" and enter the date and gestational age in weeks.
  3. Click "Calculate" to see your estimated due date.

The calculator will display your estimated due date, the date of conception, and the expected week of pregnancy.

How the Due Date Calculation Works

Pregnancy is typically considered to be 40 weeks long from the first day of the last menstrual period (LMP). The due date is calculated by adding 40 weeks (280 days) to the LMP date.

Due Date = LMP Date + 280 days

If you have an ultrasound, the calculation is based on the gestational age at the time of the scan. For example, if your ultrasound shows you're 12 weeks pregnant, the due date is calculated by adding the remaining weeks to the ultrasound date.

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

Note: Due dates are estimates. Actual delivery dates can vary by several days or more.

Examples of Due Date Calculations

Example 1: Using Last Menstrual Period

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

  • LMP Date: January 1, 2023
  • Due Date: January 1, 2023 + 280 days = October 2, 2023

Example 2: Using Ultrasound Results

If you had an ultrasound on March 15, 2023 showing you were 12 weeks pregnant:

  • Ultrasound Date: March 15, 2023
  • Gestational Age: 12 weeks
  • Remaining Weeks: 40 - 12 = 28 weeks
  • Due Date: March 15, 2023 + 28 weeks = October 10, 2023

Frequently Asked Questions

How accurate is the due date calculator?
The calculator provides an estimate based on standard medical guidelines. Actual delivery dates can vary by several days or more.
Should I use my last menstrual period or ultrasound results?
Ultrasound results are more accurate if you have them. If not, your last menstrual period is a good estimate.
What if my due date changes after the initial calculation?
If you have another ultrasound or your healthcare provider provides updated information, you should use that instead of the initial estimate.