Ovulation / Fertile Window Calculator
This tool estimates the most likely ovulation day and the surrounding fertile window based on your cycle timing. It’s useful when you want a clear, calendar-style view of the best days to try for pregnancy—or to avoid—so you can plan travel, track symptoms, and time conversations with your healthcare provider.
The Ovulation / Fertile Window Calculator helps us translate cycle patterns into practical dates, reducing guesswork and focusing efforts on the days that matter most. The goal is to support informed planning—aligning expectations, organizing schedules, and setting a simple rhythm you can follow from month to month.
Predict your ovulation day and fertile window from your cycle length and LMP, with a 6-day fertile window and calendar view.
Your cycle details
Educational use only: for planning and learning.
Predictions
Results interpretation: when this helps
- Planning conception: timing attempts across the fertile window increases chances.
- Cycle awareness: align travel or events with expected symptoms and period timing.
- Education: transparent math for understanding phase timing in a typical cycle.
Use cases & examples
Example 1: LMP 06-10-2025, cycle 28, luteal 14 → Ovulation ≈ 06-24-2025. Fertile window: 06-19 to 06-24.
Example 2: LMP 06-10-2025, cycle 32, luteal 14 → Ovulation ≈ 06-28-2025. Fertile window: 06-23 to 06-28.
Example 3: LMP 06-10-2025, cycle 26, luteal 12 → Ovulation ≈ 06-24-2025. Fertile window: 06-19 to 06-24.
Ovulation & Fertile Window — FAQ
How do you calculate my ovulation day?
We estimate ovulation as LMP + (cycle length − luteal phase). With a 28-day cycle and a 14-day luteal phase, that’s LMP + 14 days.
What is the fertile window?
The six days ending on ovulation day: the five days prior plus the day of ovulation. Sperm can live several days in fertile cervical mucus.
What if I don’t know my luteal phase length?
Leaving 14 days is a common assumption. If you learn your typical luteal length, enter it for a tighter estimate.
Why does my estimated ovulation shift when my cycle length changes?
Because we anchor on the predicted start of your next period: a longer cycle pushes ovulation later; a shorter cycle pulls it earlier.
Does this replace medical advice or lab testing?
No. It’s an educational estimate to help with planning. For diagnosis or treatment, consult your clinician.
Can travel or stress change timing?
Yes, the follicular phase can vary with stress, travel, and other factors, so real-world timing may shift.
What is the luteal phase?
The time from ovulation until the next period begins. It’s often more stable cycle-to-cycle than the first half of the cycle.
Ovulation timing, fertile days, and planning around your cycle
We estimate ovulation by pairing your cycle length with an assumed luteal phase. The aim is clarity: quick math, a readable window, and a calendar you can share.
Why luteal length matters
The luteal phase—the time from ovulation to the next period—tends to be more stable than the follicular phase. Adjusting for it shifts ovulation earlier or later within the cycle.
Making the estimate more personal
Tracking a few cycles helps refine both the average cycle length and your own luteal length. Swap in your numbers for a tighter estimate over time.
Planning tips
Many people plan attempts throughout the fertile window rather than on a single day. A copied link keeps partners and providers on the same page as plans evolve.