Calendar rule: ovulation ≈ 14 days before your next expected period (last period start + cycle length − 14 days). Shows a rough fertile window around that date.
Adds (cycle length − 14) days to the last-period date to approximate ovulation (about two weeks before the next expected period). The page also shows a rough fertile window (about two days before through two days after that estimate).
Simplified calendar estimate—not medical timing or fertility treatment guidance.
This cycle-based ovulation estimator applies the formulas described on this page to the values you enter. Outputs are not financial, tax, legal, or medical advice.
Last reviewed: 2026-04-17
No. It uses a simple calendar rule (about 14 days before your next expected period) for illustration only—not diagnosis, treatment, or contraception timing.
It is a rough range around the estimated ovulation date (about two days before through two days after). Real fertility varies by person and cycle.
For health decisions, use professional guidance and not this calculator alone.