Work out your estimated conception date from your last menstrual period or due date. Understand how conception timing affects your EDD.
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Conception occurs when a sperm fertilises an egg, typically within 24 hours of ovulation. Ovulation usually happens 14 days before the next expected period (not 14 days after LMP, unless cycles are exactly 28 days).
Sperm can survive 3–5 days in the fallopian tubes, so the fertile window extends from approximately 5 days before ovulation to the day of ovulation itself. The chance of conception is highest on the day of ovulation and the day before.