Ovulation Predictor Calculator
Predict ovulation day and fertile window from cycle length. Free ovulation predictor.
How Ovulation Timing Works
Ovulation typically occurs 14 days before the NEXT period, not 14 days after the last one. A woman with a 35-day cycle ovulates around day 21, not day 14. The fertile window spans 5 days before ovulation through 1 day after (6 days total) because sperm survives up to 5 days. The egg survives only 12-24 hours. Peak fertility is the 2-3 days immediately before ovulation.
Tracking Methods Compared
OPK strips detect the LH surge 24-36 hours before ovulation — start testing 3-4 days before expected ovulation. Basal body temperature rises 0.5-1.0F AFTER ovulation, confirming it happened but unable to predict it in advance. Cervical mucus becomes clear and stretchy before ovulation — the most accessible sign and costs nothing. For best results, combine all three methods.
The most common fertility timing mistake: waiting for a positive OPK to have intercourse. By then, the best 2-3 days are already ending. Start every-other-day intercourse 5 days before expected ovulation. Treat the OPK as confirmation, not a starting signal.
