Ovulation Window Predictor
Predicted ovulation date and fertile window from LMP and cycle length. Not medical advice.
Result
Predicted ovulation
2026-05-15
Fertile window: 2026-05-10 → 2026-05-16.
- LMP2026-05-01
- Cycle length28 days
- Days from LMP to ovulation14
- Ovulation2026-05-15
- Fertile window start (-5)2026-05-10
- Fertile window end (+1)2026-05-16
Step-by-step
- Ovulation typically occurs ~14 days before next period.
- From LMP + 28 days (next period) − 14 = 14 days from LMP = 2026-05-15.
- Fertile window: 5 days before ovulation through 1 day after.
How to use this calculator
- Enter first day of last period.
- Enter typical cycle length.
- Read ovulation date and fertile window.
About this calculator
Ovulation is roughly 14 days BEFORE the start of the next period (regardless of cycle length). The fertile window — the range during which conception is possible — extends 5 days before ovulation (sperm survives ~5 days) through ~1 day after (egg survives ~24h). This is a formula calculator; not medical advice.
Frequently asked
The luteal phase (post-ovulation) is more consistent at 14 days; the follicular phase varies. So ovulation is typically 14 days before the next period regardless of total cycle length.
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