Pregnancy dating
Start from whichever date you already have. All four routes land on the same conception window, because they all pass through the same due date.
Your dates stay on this device. Nothing you enter here is saved or sent to Flowy.
Also called conception date calculator, when did I conceive calculator. Same calculation, one page.
The calculation
All four entry points resolve to a due date first, then subtract 266 days to reach fertilization, so they can never disagree with each other. A last period date adds your cycle length minus your luteal phase to find ovulation. An ultrasound date subtracts the gestational age it reported to find day one.
The intercourse window then runs from five days before fertilization to the day itself, covering how long sperm can survive while waiting for an egg.
Good to know
Every mode here produces a window, not a point. The narrowest input still leaves a six-day intercourse span, because that is how long sperm can wait. Anyone offering a single certain date is rounding away the biology.
If your dating scan disagrees with what you calculated from your last period, the scan wins. It measures the pregnancy in front of it instead of assuming a 28-day cycle that ovulated on schedule.
Common questions
Pregnancy dating counts 280 days from the last period and 266 days from fertilization, so subtracting 266 from a due date gives the estimated conception date. The two week gap between them is why gestational age is always ahead of how long an embryo has existed.
No, and no tool can. Sperm survive up to five days, so conception can follow intercourse by most of a week. The intercourse window shown here is the honest answer: a six-day span, not a night.
An early ultrasound, because it measures the pregnancy rather than assuming a textbook cycle. A last period date is next best if your cycles are regular. Working back from an actual birth date is the loosest, because few births land exactly on 40 weeks.
Because a long cycle ovulates later. On a 35-day cycle, ovulation usually falls around day 21 rather than day 14, which moves conception and the due date a week later than a standard calculation would.
No. This is a calendar estimate with a window of several days. Anything legal, custody-related, or paternity-related needs clinical dating and testing.
