Conception Date Calculator

Most people conceive about 14 days after the start of their last period, or 38 weeks before their estimated due date.

For a 28-day cycle starting February 12, conception most likely occurred around February 26 (LMP plus 14 days). The actual window spans a few days on either side because sperm can survive up to 5 days. For longer cycles, add (cycle length minus 14) days instead, so a 32-day cycle starting February 12 would put conception around March 1.

A July due date means conception likely happened in October of the previous year. A July 1 due date corresponds to about October 8 conception, July 15 to about October 22, and July 31 to about November 7. Subtract 266 days (38 weeks) from your exact due date for the closest estimate.

Not necessarily. Since sperm can survive inside the body for up to 5 days, you may have had intercourse on Monday but not actually conceived until Wednesday.

If your due date was confirmed by an early ultrasound, the conception date estimate is highly accurate (within 3-5 days). LMP-based estimates assume ovulation on day 14, which may vary for cycles outside the typical 28-day range.

Yes. For cycles longer than 28 days, ovulation occurs later (e.g., day 21 for a 35-day cycle), shifting the conception date forward. The luteal phase remains relatively constant at 14 days, so only the follicular phase varies.

Yes. To go the other direction, add 266 days (38 weeks) to a known conception date for an estimated due date, or 280 days (40 weeks) to your LMP. Use the Pregnancy Due Date Calculator if you already know when you conceived and want a full week-by-week timeline.

No. This tool provides educational estimates based on standard obstetric formulas. It is not a substitute for professional medical guidance. Consult your healthcare provider for accurate pregnancy dating and prenatal care.

You can. Look for the "Embed" button near the top of this calculator. It lets you pick a size, border style, and color palette, then gives you an iframe tag to paste into any webpage. The widget is responsive, loads fast, and costs nothing. More details at calculory.com/services/embed-calculators.