Pregnancy Conception Calculator
The Pregnancy Conception Calculator estimates the likely date your baby was conceived, based on either your last menstrual period or a known due date.
Estimated Conception Date
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Likely Fertile Window--
How conception date is estimated
Ovulation (and likely conception) typically occurs about 14 days after the start of the last menstrual period in a standard 28-day cycle — or equivalently, about 266 days before the estimated due date:
Conception ≈ LMP + 14 days
Conception ≈ Due Date − 266 days
Example: A last period starting January 1st suggests conception around January 15th, with a fertile window roughly spanning January 13th–16th.
Accuracy
Ovulation timing varies between individuals and cycles, so this is an estimate rather than a precise date. See our Pregnancy Calculator and Due Date Calculator for related estimates.