Pregnancy Due Date & Gestational Age Calculator

How to Use This Calculator

This pregnancy due date and gestational age calculator helps you estimate when your baby will be born and how far along you are in your pregnancy. Simply enter the first day of your last menstrual period (LMP) or your conception date. The calculator will instantly provide your estimated due date, current gestational weeks and days, trimester, and the end dates of your first and second trimesters.

To get started, choose whether you want to use LMP or conception date. If you know the first day of your last period, use that option, as it is the standard method used by healthcare providers. If you know the exact date of conception (e.g., from assisted reproduction), you can use that instead. After entering the date, click Calculate to see your results.

Formula and Methodology

The calculator uses Naegele's rule, a standard formula for estimating the due date. It adds 280 days (40 weeks) to the first day of your last menstrual period. If you enter a conception date, the calculator subtracts 14 days to estimate the LMP, assuming ovulation occurs about two weeks after the start of the menstrual cycle. Gestational age is calculated by counting the days from the LMP to today, then converting to weeks and days.

Trimester milestones are determined by gestational age in days: first trimester (0–97 days), second trimester (98–195 days), and third trimester (196–280 days). These boundaries are based on standard medical definitions, though some providers may use slightly different cutoffs.

Practical Examples

For example, if your LMP was January 1, 2025, the calculator adds 280 days, giving an estimated due date of October 8, 2025. If today is April 10, 2025, the gestational age would be 99 days, or 14 weeks and 1 day, placing you in the second trimester. The end of the first trimester would be April 8, 2025, and the end of the second trimester would be July 15, 2025.

Another example: if conception occurred on February 14, 2025, the estimated LMP would be January 31, 2025. The due date would be November 7, 2025. On June 1, 2025, the gestational age would be 121 days, or 17 weeks and 2 days.

Tips and Best Practices

For the most accurate results, use the first day of your last menstrual period if you have a regular 28-day cycle. If your cycle is irregular, an early ultrasound is more reliable for dating the pregnancy. Remember that due dates are estimates—only about 4% of babies arrive on their exact due date. Most babies are born within two weeks before or after the due date.

Always consult your healthcare provider for personalized prenatal care. They may adjust your due date based on ultrasound measurements, especially if there is a discrepancy of more than a week. Use this calculator as a helpful guide, but not as a substitute for professional medical advice.