Pregnancy Conception Calculator
Estimate when your baby was conceived based on due date, last period, or ultrasound data
Calculate from Due Date
Understanding Conception Date Calculation
Our pregnancy conception calculator helps you estimate when your baby was conceived based on different reference points. Knowing your conception date can help you understand your pregnancy timeline better and estimate when fertilization likely occurred.
How Conception Works
Conception occurs when a sperm fertilizes an egg. This typically happens during a woman’s fertile window, which includes the day of ovulation and the 5 days before it. Sperm can survive in the female reproductive tract for up to 5 days, while the egg is viable for about 12-24 hours after ovulation.
Calculation Methods Explained
From Due Date
Subtracts 266 days (38 weeks) from your due date to estimate conception. This is based on the typical 40-week pregnancy counted from the last menstrual period.
From Last Period
Adds your typical cycle length minus 14 days to your last period date to estimate ovulation and conception window.
From Ultrasound
Uses ultrasound measurements of fetal development to estimate gestational age and work backward to conception.
The Fertile Window
Our calculator provides a range of possible conception dates because:
- Sperm can survive 3-5 days in the female reproductive tract
- The egg is viable for 12-24 hours after ovulation
- Ovulation timing can vary even in regular cycles
- Implantation can occur 6-12 days after conception
Did You Know?
Even with precise timing of intercourse, the exact moment of conception can’t be pinpointed because fertilization may occur hours or days after intercourse. Our calculator estimates the most probable conception date range based on biological factors.
Factors Affecting Conception Date Accuracy
- Cycle regularity: Irregular cycles make ovulation prediction less precise
- Sperm viability: Can vary from 1-5 days in the reproductive tract
- Implantation time: Fertilized egg may take 6-12 days to implant
- Early ultrasound: First trimester ultrasounds are most accurate for dating
Medical Importance
Knowing your conception date helps healthcare providers assess fetal development and establish accurate pregnancy milestones. This information can be particularly important for high-risk pregnancies or when precise dating is medically necessary.