The ovulation calculator estimates your most fertile days based on your cycle length and the date of your last menstrual period (LMP). Knowing your fertile window — the 5 days before ovulation plus the day of ovulation itself — is essential for natural family planning and pregnancy attempts.
Ovulation typically occurs 14 days before the start of the next period. For a 28-day cycle, this is around day 14. For a 32-day cycle, around day 18. The fertile window extends 5 days before ovulation because sperm can survive in the fallopian tubes for up to 5 days.
This is an estimate based on average cycle patterns. Actual ovulation varies cycle-to-cycle due to stress, illness, and hormonal factors. Use ovulation tests for confirmation.
The two days before and including ovulation day are the most fertile. Sperm can survive 3–5 days, so the 5 days before ovulation also provide meaningful conception probability.