Estimated ovulation window.
These calculators use established formulas (such as Mifflin-St Jeor for calorie needs or the Devine formula for ideal weight) to provide general estimates. They're built for a general population and don't account for individual medical conditions, medications, or circumstances. They aren't a substitute for advice from a doctor, registered dietitian, or other qualified healthcare provider — especially for anything related to pregnancy, chronic conditions, or medication dosing.
Ovulation typically occurs 14 days before the next period. Estimates ovulation day and the 5-day fertile window leading up to it.
Sperm lives up to 5 days; the egg ~24 hours. Peak odds are the day before and day of ovulation.
Calendar-based prediction assumes consistent cycle length, so accuracy drops noticeably for anyone with irregular cycles — tracking cycle length over a few months before relying on this estimate improves reliability.
28-day cycle starting Jan 1: ovulation around Jan 15, fertile window Jan 10–15.
Good for very regular cycles. Otherwise, LH ovulation kits or basal body temperature tracking are much more accurate.
Very unlikely but possible — cycle irregularity shifts timing. Use contraception if you're not trying to conceive.
Yes — significant physical or emotional stress can delay or occasionally skip ovulation entirely, which is one of several reasons calendar predictions can be off even for typically regular cycles.