Work out fertility window instantly with clear inputs, formula shown and shareable results.
Counts forward from the first day of the last period to estimated ovulation using the luteal phase length, then marks the five days before ovulation and the day after as the fertile window.
Fertile window
Ovulation day = cycle length - luteal phase; fertile window = ovulation day minus 5 to ovulation day plus 1
Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.
Sperm can survive up to five days in the female reproductive tract, while the egg is viable for about 24 hours.
Only moderately. Ovulation timing varies between cycles, so tracking basal temperature or LH gives a tighter estimate.