Conception date calculator
Work backwards from your due date or last period to the most likely day you conceived, and the fertile window around it.
Enter a date.
From intercourse to implantation
An egg lives for roughly 12–24 hours after ovulation, while sperm can survive up to five days. That gives a fertile window of about six days ending on ovulation day, which Wilcox et al. documented in their 1995 New England Journal of Medicine study. The fertilised egg then travels to the uterus and implants around 6–10 days after ovulation, which is when the body starts producing hCG, the hormone pregnancy tests detect.
Trying to conceive rather than looking back? The ovulation calculator shows your next fertile windows.
Frequently asked questions
Can a conception date calculator tell me exactly when I got pregnant?
No. It can give the most likely date and a window of about a week. Sperm can survive up to 5 days and ovulation itself varies, so sex several days before ovulation can lead to conception. Even an early scan can only date a pregnancy to within about 5–7 days.
How is the conception date calculated from a due date?
Subtract 266 days (38 weeks) from the due date. For an LMP-based estimate, add about 14 days to the first day of your last period, or (cycle length − 14) days if your cycle isn't 28 days.
Is conception the same as the day we had sex?
Not necessarily. Fertilisation happens within about 24 hours after ovulation, but sperm can wait in the reproductive tract for up to 5 days. So conception may have happened several days after intercourse.
Can a conception date prove paternity?
No. Because the fertile window spans about six days and dating has a margin of error, a conception date calculator cannot establish paternity. Only a DNA test can.