Conception Calculator
Typical range: 21-35 days (average: 28)
How Conception Works
Ovulation: An egg is released from the ovary, typically around day 14 of a 28-day cycle.
Fertilization Window: The egg can be fertilized for about 12-24 hours after release.
Sperm Survival: Sperm can survive in the reproductive tract for up to 5 days before ovulation.
Conception: The moment when sperm fertilizes the egg, which may occur hours or days after intercourse.
Understanding Dates
Related Calculators
Understanding Conception Timing
Determining when conception occurred can be helpful for establishing pregnancy dates, understanding fetal development, and planning prenatal care. While the exact moment of conception is rarely known, this calculator provides an estimate based on known dates.
Calculation Methods
Last Menstrual Period
Most common method. Counts from the first day of your last period and estimates ovulation based on cycle length.
Due Date
Works backwards from your estimated due date. Due date is typically 280 days (40 weeks) from LMP.
Ultrasound
Most accurate method. Uses gestational age from ultrasound to calculate conception date.
Why Conception Date Differs from Intercourse Date
- Sperm can survive in the female reproductive tract for up to 5 days
- Conception occurs when sperm meets egg, not during intercourse
- The egg is only viable for 12-24 hours after ovulation
- Multiple instances of intercourse during the fertile window can all potentially lead to conception
Gestational Age vs. Fetal Age
Medical professionals use gestational age (counted from LMP) rather than fetal age (from conception) because the LMP date is more reliably known. Gestational age is typically about 2 weeks longer than fetal age.
Important Note
This calculator provides estimates only. The actual conception date can vary based on individual cycle variations, sperm survival time, and other factors. For precise dating, especially for medical decisions, consult with your healthcare provider who may use ultrasound measurements.
Frequently Asked Questions
How is the conception date calculated?
Conception date is estimated by determining when ovulation likely occurred. For a typical 28-day cycle, ovulation happens around day 14 after the first day of your last menstrual period (LMP). Since sperm can survive up to 5 days and the egg is viable for 12-24 hours, conception typically occurs within this fertile window around ovulation.
Why might my conception date differ from when I had intercourse?
Conception doesn't necessarily occur during intercourse. Sperm can survive in the reproductive tract for up to 5 days, waiting for the egg to be released. If you had intercourse 3 days before ovulation, conception would occur on ovulation day, not the day of intercourse. This is why the fertile window spans several days.
What is the difference between gestational age and fetal age?
Gestational age counts from the first day of your last menstrual period (LMP) and is used for all medical purposes. Fetal age (also called embryonic age) counts from actual conception and is about 2 weeks shorter than gestational age. When doctors say you're 8 weeks pregnant, they mean 8 weeks gestational age, but the embryo has only been developing for about 6 weeks.
Which method is most accurate for determining conception date?
Early ultrasound dating (before 12 weeks) is the most accurate method for determining conception date, with accuracy within 3-5 days. LMP-based calculations assume a regular 28-day cycle with ovulation on day 14, which varies among women. If your cycles are irregular, ultrasound dating is particularly important for accurate dating.