Due Date Calculator

Calculate your pregnancy due date based on last menstrual period or conception date.

Calculate Due Date

First day of your last period

Range: 21-35 days (default: 28)

Enter your information to calculate your due date and pregnancy timeline with detailed analysis and charts.

Complete User Guide

What is a Due Date?

A due date (also called expected date of delivery or EDD) is the estimated date when a pregnant woman is most likely to give birth. It's calculated as 40 weeks (280 days) from the first day of the last menstrual period (LMP).

The due date is an estimate, not an exact date. Only about 5% of babies are born exactly on their due date, with most babies born within two weeks before or after the due date.

How Due Date is Calculated

Naegele's Rule (From LMP)

The most common method: Add 1 year, subtract 3 months, and add 7 days to the first day of your last menstrual period. Simplified: Add 280 days (40 weeks) to LMP.

Formula: Due Date = LMP + 280 days

From Conception Date

If you know the conception date, add 266 days (38 weeks) to calculate the due date. This accounts for the typical 2-week period between LMP and conception.

Formula: Due Date = Conception Date + 266 days

How to Use This Calculator

  1. Choose your calculation method: From Last Menstrual Period or From Conception Date
  2. If using LMP method, enter the first day of your last menstrual period and your cycle length (default: 28 days)
  3. If using conception date method, enter the estimated date of conception
  4. Click 'Calculate' to see your results
  5. Review your due date, pregnancy timeline, trimester information, and milestones
  6. Use the charts to visualize your pregnancy progress

Understanding Your Results

Due Date

The estimated date when your baby is due. This is calculated as 280 days (40 weeks) from your last menstrual period or 266 days from conception.

Conception Date

The estimated date when conception likely occurred. This is typically 14 days after the first day of your last period (or cycle_length - 14 days for variable cycles).

Last Menstrual Period (LMP)

The first day of your last menstrual period. This is the standard starting point for calculating pregnancy weeks and due date.

Weeks and Days Pregnant

The number of weeks and days since your last menstrual period. Pregnancy is counted from LMP, not from conception.

Trimester

Your current trimester: First (weeks 1-13), Second (weeks 14-27), or Third (weeks 28-40).

Progress Percentage

The percentage of your pregnancy completed based on a full 40-week (280-day) term.

Pregnancy Milestones

First Trimester End (13 weeks)

End of the first trimester. Major organ development is complete, and the risk of miscarriage decreases significantly.

Viability Week (24 weeks)

The point at which a baby has a chance of survival outside the womb with medical intervention.

Second Trimester End (27 weeks)

End of the second trimester. Baby's movements are strong, and most major development is complete.

Full Term (37 weeks)

Baby is considered full-term and ready for birth. Lungs and other organs are mature.

Due Date Accuracy

Due dates are estimates, not exact dates. Several factors can affect the accuracy:

  • Irregular menstrual cycles
  • Uncertainty about the exact date of LMP
  • Variations in the length of pregnancy (normal range: 37-42 weeks)
  • Individual differences in fetal development

Healthcare providers often use ultrasound measurements to refine the due date, especially in early pregnancy.

Important Notes

  • Due dates are estimates. Only about 5% of babies are born exactly on their due date. Most babies are born within two weeks before or after the due date.
  • Pregnancy is counted from the first day of your last menstrual period (LMP), not from conception. This is why pregnancy is said to last 40 weeks even though conception occurs about 2 weeks after LMP.
  • If your cycle is longer or shorter than 28 days, adjust the cycle length in the calculator for more accurate results.
  • This calculator is for educational and informational purposes only. Always consult with healthcare providers for accurate pregnancy dating, especially for medical decisions and prenatal care.

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