Estimate your conception date and fertile window based on your due date or last menstrual period.
Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making any health-related decisions or starting any diet or exercise programme.
Conception ≈ Due date − 266 days
LMP = Due date − 280 days
Likely intercourse window ≈ conception − 5 days to conception + 1 day
It is usually accurate to within a few days, but no calculator can give an exact date. Ovulation timing varies from cycle to cycle, sperm can survive up to five days, and due dates themselves are estimates. If your due date came from a first-trimester ultrasound, the conception estimate will be more reliable than one based on your period alone.
No. Because sperm can live for up to five days and ovulation timing varies, a conception window usually spans about a week. Two acts of intercourse a few days apart can both fall inside it. Only a DNA paternity test can establish paternity.
Pregnancy is dated from the first day of the last menstrual period, about two weeks before ovulation and conception in a typical 28-day cycle. So a 280-day (40-week) pregnancy counted from the LMP is about 266 days (38 weeks) from conception.
The estimated conception date stays the same, because it is counted back from the due date. Only the implied LMP date assumes a 28-day cycle. With a longer cycle your actual LMP was earlier than shown; with a shorter cycle it was later.
Conception typically occurs around ovulation, which is approximately 14 days before the start of the next menstrual period. If you know your due date, subtract 266 days to estimate conception. If you know your LMP, ovulation likely occurred around day 14 of a 28-day cycle. These are estimates — exact conception timing is difficult to pinpoint.
Did you know?
Conception can occur from intercourse that happened up to 5 days before ovulation, because sperm can survive that long in the female reproductive tract.
Understanding conception timing has been a subject of study since ancient civilizations. Aristotle believed conception was most likely during menstruation. It was not until the 1920s that scientists correctly identified the fertile window around ovulation.
The exact moment of conception is rarely known, even for planned pregnancies, because sperm can fertilize an egg up to 5 days after intercourse.
Implantation — when the fertilized egg attaches to the uterine wall — occurs 6–12 days after conception.
Home pregnancy tests detect the hormone hCG, which is first produced after implantation, typically 10–14 days after conception.