When Was My Baby Due Date Calculator

Determine when your baby was due based on your last menstrual period. This calculator helps you estimate your due date by subtracting the average gestation period from your last period date.

How to Use This Calculator

To calculate when your baby was due:

Enter the date of your last menstrual period in the "Last Period Date" field.
Click the "Calculate" button.
Review the estimated due date and conception date.

The calculator will display your estimated due date and the approximate date of conception based on the average gestation period of 40 weeks.

How the Due Date Calculation Works

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

Due Date = Last Period Date + 280 days

The conception date is estimated by subtracting 14 days from the last period date, assuming ovulation occurs about 14 days before the start of the menstrual cycle.

Conception Date ≈ Last Period Date - 14 days

Note: These calculations are estimates. Actual due dates may vary by several days. Always consult with your healthcare provider for personalized medical advice.

Example Calculation

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

Estimated due date: January 1, 2023 + 280 days = October 8, 2023
Estimated conception date: January 1, 2023 - 14 days = December 18, 2022

This example shows how the calculator works with a specific date. You can enter your own last period date to get personalized results.

Frequently Asked Questions

How accurate is this due date calculator?

This calculator provides an estimate based on average gestation periods. Actual due dates may vary by several days. For precise medical information, consult your healthcare provider.

Can I use this calculator for multiple pregnancies?

Yes, you can use this calculator for each pregnancy separately by entering the date of your last menstrual period for each pregnancy.

What if I don't remember the exact date of my last period?

If you're unsure of the exact date, you can estimate based on your menstrual cycle pattern. The calculator will still provide a useful estimate.

How does this calculator determine the conception date?

The calculator estimates conception by subtracting 14 days from your last period date, assuming ovulation occurs about 14 days before the start of your menstrual cycle.