🌸 Pregnancy & Baby

Conception Date Calculator

Work backwards from your due date or last menstrual period to estimate when conception likely occurred. Calculate your estimated ovulation date and conception window.

28 days
Estimated Conception Date
—
—Estimated Ovulation
—Window Starts
—Window Ends
—Est. LMP

Estimated dates only. Actual conception can only be confirmed through ultrasound and clinical assessment. Cycle length, ovulation timing, and sperm survival all introduce natural variation. Consult your midwife or obstetrician for clinical dating.

How conception date is estimated

Conception occurs when a sperm fertilises an egg. For a standard 28-day cycle, ovulation typically occurs around day 14 (counting from the first day of the last period). Sperm can survive 3–5 days in the female reproductive tract, while an egg is viable for approximately 12–24 hours after ovulation, creating a fertile window of roughly 5–7 days.

Working backwards from a due date: subtract 266 days (38 weeks) from the EDD to estimate conception, or subtract 280 days (40 weeks) to reach the LMP, then add the ovulation day (cycle length − 14) to find estimated conception.

Sources

  1. Wilcox AJ, et al. "Timing of sexual intercourse in relation to ovulation." New England Journal of Medicine. 1995;333:1517–1521.
  2. ACOG. "Methods for Estimating the Due Date." Committee Opinion No. 700. 2017.