Conception Date Calculator: When Did I Get Pregnant?

How conception date is estimated

Conception happens on the day of ovulation or shortly after. The calculator estimates ovulation like this:

• From your last period: in a 28-day cycle, ovulation happens about 14 days after the first day of your period. If your cycle is longer or shorter, the calculator adjusts for the difference.
• From your due date: the same assumptions are applied in reverse. If your provider gave you a date, especially one adjusted after an ultrasound, this is the more reliable option.

Why a window, not a single day

Sperm can survive in the reproductive tract for several days, so the day of conception and the day you had sex are often different. A pregnancy can come from sex during the 5 days before ovulation or on ovulation day itself. The calculator shows that window day by day; the darkest day is your estimated ovulation and conception day.

Even that window has some give: ovulation can shift by a few days from one cycle to the next in the same person.

“Who’s the father?”

It’s one of the main reasons people look up their conception date, so here’s the honest answer: if the possible dates are only days or a few weeks apart, neither this calculation nor an ultrasound can reliably tell them apart. The calculation is an estimate, and ultrasound dating has a margin of a few days too.

Only a DNA test can give a definite answer. It can be done after birth and, in some cases, during pregnancy. You can talk this through confidentially with an OB-GYN, who can explain the options without judgment.

Dating by ultrasound

A first-trimester ultrasound measures the baby and dates the pregnancy more accurately than a period-based calculation. If your provider gave you a due date based on that scan, choose “Due date from your provider” and your estimated conception date will be based on the scan too.

With IVF the date of fertilization is already known; use our IVF due date calculator instead.