Estimate when conception occurred based on your due date, last menstrual period, or ultrasound measurements. Get your probable conception date and fertile window range.
Conception date is when the egg was fertilized by sperm. Since sperm can survive in the female reproductive tract for 3-5 days, the exact conception date may differ from the date of intercourse. Our calculator uses three methods to estimate your conception date:
If you know your due date, subtract 266 days (38 weeks) to estimate conception. This assumes a full-term pregnancy of 40 weeks from the last menstrual period.
Formula: Due Date - 266 days = Estimated Conception Date
For women with regular 28-day cycles, conception typically occurs around day 14 (ovulation day). Add 14 days to your LMP date to estimate conception. The fertile window extends from 5 days before to 1 day after ovulation.
First-trimester ultrasounds provide the most accurate gestational age. The calculator works backward from the ultrasound-determined due date to estimate conception, typically 266 days before the EDD.
The fertile window is the period when pregnancy is most likely to occur. It includes the days leading up to and including ovulation:
The fertile window typically spans 6 days: the 5 days before ovulation and ovulation day itself. Sperm can survive up to 5 days in the female reproductive tract, waiting for the egg to be released.
The 2-3 days before ovulation and ovulation day have the highest pregnancy rates. Having intercourse during this window maximizes the chances of conception.
After ovulation, the egg is viable for only 12-24 hours. If not fertilized during this time, the egg disintegrates and pregnancy cannot occur until the next cycle.
Sperm can survive in the female reproductive tract for 3-5 days under optimal conditions. This is why intercourse before ovulation can still result in pregnancy.
Women with cycles shorter or longer than 28 days ovulate at different times. A 35-day cycle means ovulation around day 21, while a 21-day cycle means ovulation around day 7. This affects conception date estimates.
Conditions like PCOS can cause irregular ovulation, making it harder to pinpoint conception. Women with irregular cycles should rely more on ultrasound dating for accuracy.
If you had intercourse multiple times during your fertile window, it's impossible to know which specific encounter resulted in conception. The calculator provides a range of possible dates.
IVF and IUI procedures have precisely known conception dates. For IVF, conception is the date of embryo transfer (adjusted for embryo age). For IUI, it's typically the insemination date.
Knowing your conception date can be helpful for several reasons:
Understanding your fertile window can help determine possible paternity, though DNA testing is the only definitive method. The conception calculator provides a range of possible dates.
Knowing when you conceived helps you understand your cycle better and can assist in planning future pregnancies by identifying your most fertile days.
Healthcare providers may ask about possible conception dates to assess exposure to medications, alcohol, or other substances during early pregnancy when organs are forming.
Many parents simply want to know when their baby was conceived as part of their pregnancy journey and family story.
It's important to understand the difference between conception and implantation:
Conception occurs when sperm fertilizes the egg, typically in the fallopian tube. This happens within 12-24 hours after ovulation. The fertilized egg (zygote) begins dividing immediately.
Implantation occurs 6-12 days after conception when the embryo attaches to the uterine wall. This is when pregnancy officially begins and hCG hormone production starts, making pregnancy tests positive.
While you can't feel conception happening, some women notice early pregnancy signs within 1-2 weeks:
Light spotting 6-12 days after conception, caused by the embryo attaching to the uterine lining. It's typically lighter and shorter than a period.
Hormonal changes can cause breast sensitivity, swelling, or tingling within 1-2 weeks of conception.
Increased progesterone levels can cause extreme tiredness as early as one week after conception.
Morning sickness typically starts 2-8 weeks after conception, though some women experience it earlier.
It's nearly impossible to know the exact day of conception unless you used assisted reproductive technology. The calculator provides an estimated date and fertile window range based on available information.
Not necessarily. Sperm can survive in the female reproductive tract for up to 5 days, so conception may occur several days after intercourse. The conception date is when the egg was actually fertilized.
Conception calculators provide estimates within a 5-7 day window. For women with regular cycles, the estimate is more accurate. Ultrasound-based calculations are the most reliable method.
Pregnancy is highly unlikely outside the fertile window. The egg is only viable for 12-24 hours after ovulation, and sperm survive up to 5 days. Conception must occur within this timeframe.
Irregular periods make conception date estimation less accurate. Your healthcare provider will rely on early ultrasound measurements to determine gestational age and work backward to estimate conception.
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