You most likely conceived around
Sperm can survive up to 5 days, so intercourse during the fertile window could have led to this pregnancy. No calculator can pinpoint the exact day.
How is the conception date calculated?
Conception usually happens within a day of ovulation. In a 28-day cycle, ovulation is around day 14, which is 266 days (38 weeks) before the due date.
- From your due date: due date minus 266 days.
- From your last period: first day of last period plus your cycle length minus 14 days. This assumes the second half of your cycle (the luteal phase) lasts about 14 days.
Why the result is a window, not one day
Sperm can live in the body for up to 5 days, and an egg survives for about 12 to 24 hours after ovulation. So the intercourse that led to pregnancy could have happened on any day from about 5 days before ovulation to the day after. The calculator shows this fertile window.
Can this tell me who the father is?
No. Because of the fertile window, and because due dates are estimates, a conception date calculator cannot reliably show the day of conception or the father. Only a paternity DNA test can do that.
Frequently asked questions
How accurate is a conception date calculator?
It gives a good estimate when your cycles are regular and your due date is based on an early ultrasound. With irregular cycles the estimate can be off by a week or more.
Is conception the same as implantation?
No. Implantation happens later, when the fertilised egg attaches to the lining of the uterus, usually about 6 to 12 days after ovulation.
My cycle is longer than 28 days. Does that change the date?
Yes. With a longer cycle you ovulate later, so the calculator moves the conception date later when you use the last period option.
Is my information saved?
No. The calculation runs in your browser and nothing is stored.