Conception typically happens around ovulation, roughly 14 days after the first day of the last menstrual period (LMP) in a 28-day cycle. Or work backwards from your expected due date: conception ≈ due date − 266 days.
Estimated conception date
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Fertile window
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Estimated due date
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Current gestational age
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Important caveats
This is an estimate. Sperm can survive 3–5 days in the reproductive tract, so the actual date of conception can fall within a window, not a single day.
If you have irregular cycles, the LMP-based method becomes less reliable — an ultrasound dating scan in the first trimester is the gold standard.
The calculator assumes a standard ovulation timing of cycle length minus 14 days.