Ovulation Calculator
Estimate ovulation and your fertile window using your last period date and average cycle length. An ovulation calculator estimates your ovulation date and fertile window based on your last period start date (LMP) and average cycle length. Cycles vary and ovulation can shift month to month. Use this as an estimate, not a medical prediction.
Inputs
days
If unsure, 14 days is a common default.
days
Estimated dates
Ovulation dateJan 29, 2026
Fertile windowJan 24–Jan 30, 2026
Next period (estimate)Feb 12, 2026
Due date (from ovulation, estimate)Oct 22, 2026
These are estimates. Ovulation timing can vary by cycle.
How to use it
- Enter the first day of your last menstrual period (LMP).
- Enter your average cycle length in days.
- Optionally adjust luteal phase length if you know it.
- Review estimated ovulation date and fertile window range.
Key formulas
- Estimated ovulation timing (rule of thumb)
- Ovulation ≈ LMP + (cycleLength − lutealLength) days (often lutealLength ≈ 14)
FAQ
The fertile window is the range of days when pregnancy is most likely. Many tools estimate it as the 5 days before ovulation plus ovulation day (sometimes plus 1 day after).
It’s an estimate. Stress, travel, illness, and hormonal changes can shift ovulation. Ovulation tests and tracking basal body temperature may provide more personalized insight.
Predictions become less reliable when cycle length varies widely. Consider using the average of several recent cycles and treat results as a rough guide.
The luteal phase is the time from ovulation to the next period. It’s often around 14 days but can vary. If you know yours, you can use it for a better estimate.
Some ovulation tools provide a due date estimate based on an estimated conception/ovulation date. It’s still an estimate; confirm with a healthcare professional.
Sources
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Disclaimer
For informational use only and not medical advice. Cycle and ovulation timing vary. Consult a healthcare professional for medical guidance.