Most Likely Conception Date
Enter your information above
Conception Window
MMM DD - MMM DD, YYYY
Ovulation Date
MMM DD, YYYY
How to Calculate Your Conception Date
Knowing your conception date can provide valuable insight into your pregnancy timeline, help you understand your baby's developmental milestones, and address important questions about early pregnancy exposures. Our conception calculator works backward from your due date or current pregnancy week to estimate when fertilization most likely occurred.
Conception Date vs. Date of Intercourse
Many people are surprised to learn that conception doesn't necessarily happen on the same day as intercourse. Sperm can survive in the female reproductive tract for up to 5 days, waiting for an egg to be released during ovulation. This means that if you had intercourse on Monday and ovulated on Thursday, conception would have occurred on Thursday—not Monday. Our calculator estimates both your likely conception date and the broader window of intercourse that could have led to pregnancy, typically spanning about 6 days. For cycle planning, try our ovulation calculator.
Why Does My Ultrasound Show a Different Date?
It's common for early ultrasound measurements to differ from LMP-based calculations by a few days or even a week. This happens because not everyone ovulates on day 14 of their cycle, and embryo growth can vary slightly in the first weeks. If there's a significant discrepancy (more than a week), your healthcare provider may adjust your due date based on the ultrasound, which measures the embryo's crown-rump length. This adjusted date then becomes your official due date for tracking purposes. Don't be alarmed if your dates are revised—this is a normal part of prenatal care and helps ensure accurate monitoring of your baby's growth.
Conception Dates with IVF and Fertility Treatments
For IVF pregnancies, the conception date is more precisely known since egg retrieval and fertilization happen in a controlled environment. If you had a Day 5 blastocyst transfer, your conception date would be 5 days before the transfer date. For Day 3 embryo transfers, conception occurred 3 days before transfer. With frozen embryo transfers (FET), the same calculation applies based on the embryo's age at freezing. Our IVF due date calculator is specifically designed to handle these calculations.
Using Conception Date for Paternity Questions
While conception calculators can narrow down the timeframe when pregnancy occurred, they cannot definitively answer paternity questions. The fertile window spans about 6 days, and individual variations in cycle length and ovulation timing add uncertainty. If paternity is a concern, DNA testing is the only way to get a definitive answer. Prenatal paternity tests can be performed as early as 7-8 weeks into pregnancy through non-invasive methods that analyze fetal DNA in the mother's blood. However, using conception date ranges can help you understand the possible timeline before deciding on next steps.
Frequently Asked Questions
Can I determine my exact conception date?
Conception dates are estimates because ovulation timing varies and sperm can survive for several days. Even with perfect cycle tracking, you can typically only narrow it down to a 2-3 day window. Ultrasound measurements can help refine this estimate but won't give you an exact date either.
Why is gestational age different from fetal age?
Gestational age counts from your last menstrual period (LMP), which is about 2 weeks before conception. Fetal age (also called embryonic age) counts from conception. When you're "8 weeks pregnant," your baby is actually about 6 weeks old. Medical professionals use gestational age because LMP is easier to identify.
How accurate is the conception date from my due date?
If your due date was determined by early ultrasound, the conception date calculation is fairly accurate—usually within 3-5 days. If your due date is based solely on LMP, there's more variability depending on your actual ovulation date. Either way, expect a range rather than a specific date.
I had intercourse multiple times—which one resulted in pregnancy?
It's usually impossible to know which specific instance of intercourse led to conception. Any intercourse within your fertile window (about 5 days before ovulation through ovulation day) could have resulted in pregnancy. The sperm that fertilized the egg may have arrived days before the egg was released.
Can medications or alcohol exposure be tracked using conception date?
Yes, knowing your conception date helps identify what exposures occurred during the critical early development period. Most organ development happens between weeks 3-8 after conception. If you have concerns about exposures, discuss the specific timing with your healthcare provider who can provide guidance based on your conception date range.
What if I don't know my due date or last period?
If you don't have either date, an ultrasound is the best way to determine how far along you are. Early ultrasounds (before 12 weeks) are most accurate for dating. Once you have a due date from ultrasound, you can use our calculator to estimate conception. Contact your healthcare provider to schedule a dating ultrasound.