Menstrual Cycle Basics
A typical cycle is 21–35 days (adults). Ovulation — release of an egg — usually occurs ~14 days before the next period in many regular cycles, not always "day 14" from the last period.
Fertile window often spans ~5 days before ovulation plus the day of ovulation — sperm can survive several days in the body.
Calendar Methods
Calendar apps estimate ovulation from cycle length and LMP — useful for rough planning, not contraception or precise conception timing.
| Better precision | Method |
|---|---|
| LH strips | Surge ~24–36h before ovulation |
| Basal body temp | Rise after ovulation (confirms retrospectively) |
| Ultrasound | Clinical monitoring |
Irregular Cycles
PCOS, stress, travel, and hormonal changes disrupt prediction. If cycles vary by more than ~7 days, calendar estimates are unreliable — see a gynecologist or reproductive specialist.
This tool is educational, not medical advice.
How to Use This Ovulation Calculator
Enter cycle length and last period start (or similar inputs). Review estimated ovulation and fertile window — confirm with tests or providers if timing matters for health or conception.