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Conception Calculator

When a baby was most likely conceived, from the due date, the last period or the birth date.

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Result…

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How it's calculated

Conception ≈ due date − 266 days (38 weeks)
Conception ≈ last period + 14 days (+ cycle length − 28)
From a birth: conception ≈ birth date − weeks at birth × 7 + 14 days

Conception usually happens within a day of ovulation, about two weeks after the last period began, and 38 weeks before the due date. Sperm can live up to five days, so the possible window is about a week wide even when the dates are exact. Ultrasound-dated pregnancies give the best estimate.

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