Ovulation Window
Estimate the likely ovulation day and fertile window from the first day of your last period and your average cycle length. It assumes ovulation about 14 days before the next period — a general estimate, not medical advice, and not a contraceptive method.
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Worked example
Ovulation: 2026-07-15 · Fertile: 07-10 – 07-16
Inputs
- Last period
2026-07-01 - Cycle length
28
Frequently asked
How is ovulation estimated?
By counting back 14 days from the expected next period (cycle length minus 14 days after the last period).
How wide is the fertile window?
Roughly the five days before ovulation plus the day itself, since sperm can survive several days.