Conception Calculator

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

Calculate Conception Date

Enter your expected due date

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

Complete User Guide

What is Conception?

Conception occurs when a sperm fertilizes an egg, typically happening during ovulation. This is the moment when pregnancy begins, and it usually occurs about 14 days after the start of your last menstrual period (LMP) in a 28-day cycle.

The conception date is important for tracking fetal development, understanding pregnancy milestones, and calculating your due date. However, it's important to note that the exact moment of conception is difficult to determine precisely.

How Conception Date is Calculated

From Due Date

Conception typically occurs approximately 266 days (38 weeks) before the due date. This is calculated by subtracting 266 days from your expected due date.

Formula: Conception Date = Due Date - 266 days

From Last Menstrual Period

Conception typically occurs around 14 days before your next expected period. For a 28-day cycle, this is 14 days after the first day of your last period.

Formula: Conception Date = Last Period + (Cycle Length - 14 days)

How to Use This Calculator

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

Understanding Your Results

Conception Date

The estimated date when conception likely occurred. This is typically within a 5-6 day window around ovulation when the egg is viable for fertilization.

Last Menstrual Period (LMP)

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

Due Date

The estimated date when your baby is due. This is calculated as 280 days (40 weeks) from the first day of your last menstrual period.

Weeks and Days Pregnant

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

Trimester

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

Progress Percentage

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

Pregnancy Trimesters

First Trimester (Weeks 1-13)

Early development, organ formation, and initial fetal growth. Many women experience morning sickness and fatigue during this period.

Key milestones: Heartbeat begins, major organs form, baby's sex is determined

Second Trimester (Weeks 14-27)

Rapid growth, movement felt, and visible baby bump. Often called the 'honeymoon period' of pregnancy.

Key milestones: Baby movements felt, anatomy scan, baby can hear sounds

Third Trimester (Weeks 28-40)

Final growth phase, preparation for birth, and increased discomfort. Baby gains most weight during this period.

Key milestones: Baby reaches full term (37 weeks), lungs mature, ready for birth

Understanding the Conception Window

Conception can occur within a 5-6 day window around ovulation:

  • Sperm can survive in the female reproductive tract for up to 5 days
  • The egg is viable for fertilization for about 12-24 hours after ovulation
  • The most fertile window is typically 2-3 days before ovulation and the day of ovulation
  • The calculator provides an estimated conception date, but actual conception may have occurred within a few days of this date

Important Notes

  • Conception dates are estimates. The exact moment of conception is difficult to determine, and actual conception may have occurred within a 5-6 day window around the calculated date.
  • Pregnancy is typically 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.
  • Individual cycle lengths vary. 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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