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📅 Ovulation Calculator

Estimate your ovulation date and fertile window based on your last menstrual period and average cycle length. Identify your most fertile days to help with family planning.

Medical Disclaimer: This calculator provides estimates only. Consult your doctor for family planning advice.

Typical range: 21–35 days

How the Calculation Works

Ovulation Day = LMP + (Cycle Length − 14) days
Fertile Window Start = Ovulation − 5 days
Fertile Window End = Ovulation + 1 day
Next Period = LMP + Cycle Length days

Ovulation typically occurs 14 days before the next period. The 6-day fertile window includes 5 days before ovulation and the ovulation day itself, as sperm can survive up to 5 days.

How to Use This Calculator

  1. 1
    Enter Your Last Period Start Date
    Input the first day of your most recent menstrual period. This is day 1 of your cycle.
  2. 2
    Set Your Average Cycle Length
    Enter how many days your cycle typically lasts. The default is 28 days but 21–35 is normal.
  3. 3
    Review Your Results
    See your estimated ovulation date, fertile window, and the 35-day cycle visual overview.
  4. 4
    Plan Accordingly
    Use the results alongside other fertility signs like cervical mucus changes and basal body temperature.

Real-World Example

LMP: January 1, Cycle length: 28 days

Ovulation = Jan 1 + (28 − 14) = January 15
Fertile Window Start = Jan 15 − 5 = January 10
Fertile Window End = Jan 15 + 1 = January 16
Next Period = Jan 1 + 28 = January 29

Frequently Asked Questions

Ovulation typically occurs about 14 days before your next period starts. For a 28-day cycle this is around day 14. For shorter or longer cycles, it shifts accordingly — use this calculator to find your personal estimate.

The fertile window is the 6-day period when pregnancy is possible: the 5 days before ovulation and the ovulation day itself. Sperm can survive in the reproductive tract for up to 5 days, making the days leading up to ovulation also fertile.

This tool provides estimates based on average cycle patterns. Real ovulation can vary by several days due to stress, illness, hormones, or irregular cycles. For higher accuracy, combine this with basal body temperature tracking or ovulation predictor kits.

Common ovulation signs include clear, stretchy cervical mucus (like raw egg white), a slight rise in basal body temperature, mild pelvic pain or cramping (mittelschmerz), and increased libido. Some people also experience light spotting.

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