Ovulation Calculator

Estimate your most fertile days and ovulation window based on your cycle length.

28 days
21 days45 days
Average cycle is 28 days. Most people ovulate 12-16 days before their next period starts.

Ovulation Date

May 14, 2026

today

Fertile WindowMay 9, 2026 - May 15, 2026
Next PeriodMay 28, 2026
Cycle Length28 days
3-Month Fertility Calendar
Cycle StartFertile WindowOvulationNext Period
Apr 30, 2026May 9, 2026 - May 15, 2026May 14, 2026May 28, 2026
May 28, 2026Jun 6, 2026 - Jun 12, 2026Jun 11, 2026Jun 25, 2026
Jun 25, 2026Jul 4, 2026 - Jul 10, 2026Jul 9, 2026Jul 23, 2026

How to Use the Ovulation Calculator

  1. Enter the first day of your last menstrual period (LMP). This is Day 1 of your cycle, when bleeding begins. Do not use the last day of your period.
  2. Set your typical cycle length. The average is 28 days, but normal cycles range from 21 to 45 days. If your cycles vary, use your average over the past 3-6 months. Shorter cycles mean earlier ovulation; longer cycles mean later ovulation.
  3. Read the fertile window. The calculator estimates your ovulation date (typically 14 days before your next period) and marks the 6-day fertile window. The 2-3 days immediately before ovulation have the highest conception probability.

These are estimates based on average cycle patterns. Actual ovulation can vary by several days due to stress, illness, and other factors.

Ovulation Timing and Fertility Window

Ovulation day = LMP date + (cycle length - 14)

Fertile window: 5 days before ovulation
through 1 day after ovulation (6 days total)

Example: LMP = April 1, cycle = 28 days
Ovulation = April 1 + (28 - 14) = April 15
Fertile window = April 10-16

Conception probability by timing relative to ovulation:

TimingConception Probability
5 days before ovulation~10%
3 days before ovulation~27-33%
2 days before ovulation~29-34%
1 day before ovulation~26-31%
Day of ovulation~15%
1 day after ovulation~5% (egg viable)
2+ days after ovulationEssentially 0%

Frequently Asked Questions

Ovulation typically occurs 14 days before the start of your next period (not 14 days after your LMP). For a 28-day cycle, that is around day 14. For a 32-day cycle, it is around day 18. For a 24-day cycle, it is around day 10. The luteal phase (ovulation to next period) is relatively fixed at 12-16 days for most women, while the follicular phase (LMP to ovulation) varies. This is why longer cycles push ovulation later.

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