Fertility Window Calculator
First Day of Last Period
Cycle Length (days)
The fertility window is the 6-day period when conception is possible — 5 days before ovulation and ovulation day itself. Ovulation typically occurs 14 days before the next period.
- 1Ovulation ≈ Cycle length − 14 days from LMP
- 2Fertile window = Ovulation − 5 days to Ovulation day
- 3Sperm survive 3–5 days; egg survives ~12–24 hours
- 4OPK tests and basal body temperature confirm ovulation
30-day cycle, LMP 1 January=Ovulation ≈ Jan 16; Fertile window: Jan 11–16
| Cycle | Ovulation | Fertile window |
|---|---|---|
| 24 days | Day 10 | Days 5–10 |
| 28 days | Day 14 | Days 9–14 |
| 32 days | Day 18 | Days 13–18 |
| 35 days | Day 21 | Days 16–21 |
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