Baby Prediction Calculator 2021

Use this baby prediction calculator to estimate your due date based on your last menstrual period (LMP) or ultrasound date. The calculator provides a 2021-specific estimate and explains the factors that can affect your actual due date.

How to Use This Calculator

To get an accurate prediction of your baby's due date:

Enter your last menstrual period (LMP) date or your ultrasound date
Select whether you're using LMP or ultrasound date
Click "Calculate" to see your estimated due date
Review the factors that might affect your actual due date

The calculator uses standard pregnancy duration of 40 weeks (280 days) from the first day of your last menstrual period. However, individual pregnancies may vary.

How Baby Due Dates Are Calculated

The standard calculation method adds 280 days (40 weeks) to your last menstrual period (LMP) date to estimate your due date. This is based on the average length of a full-term pregnancy.

Due Date = LMP Date + 280 days

For example, if your LMP was January 1, 2021, your due date would be October 8, 2021 (280 days later).

Ultrasound dates are typically more accurate than LMP-based estimates because they measure the baby's development stage. The calculator can use either method based on your preference.

Factors Affecting Due Date

Several factors can affect your actual due date compared to the estimated one:

Pregnancy length: Some babies are born early (preterm) or late (post-term)
Multiple pregnancies: Twins or higher-order multiples may have different due dates
Medical conditions: Certain health issues can affect pregnancy duration
Ultrasound accuracy: Early ultrasounds may have less precise measurements

Remember that due dates are estimates. The actual birth date can vary by several weeks in either direction.

Example Calculations

Here are two example calculations using different methods:

Example 1: Using Last Menstrual Period

If your LMP was March 15, 2021:

Due Date = March 15, 2021 + 280 days Due Date = December 10, 2021

Example 2: Using Ultrasound Date

If your ultrasound showed your baby was 12 weeks old on April 1, 2021:

Due Date = April 1, 2021 + (40 - 12) weeks Due Date = April 1, 2021 + 28 weeks Due Date = October 20, 2021

FAQ

Is the due date calculator 100% accurate?: No, due dates are estimates. Individual pregnancies can vary by several weeks in either direction.
Can I use this calculator for multiple pregnancies?: Yes, but each baby may have a slightly different due date in multiple pregnancies.
How often should I check my due date?: It's good to check with your healthcare provider every prenatal visit to monitor your baby's development.
What if my due date changes after the initial estimate?: If your healthcare provider provides a new estimate, use that instead of the original calculation.