Ovulation Calculator & Tracker

Predict your next period start, identify your highly fertile window, estimate peak ovulation days, and track long-term predictions on an interactive cycle calendar. 100% private, client-side execution.

Cycle Parameters
SuMoTuWeThFrSa
28 days
20 days45 days
14 days
10 days20 days

The luteal phase is the days from ovulation to the start of your next period. Standard is 14 days.

Key Cycle Thresholds
EXPECTED NEXT PERIOD Calculating...
EARLIEST PREGNANCY TEST Calculating...
ESTIMATED DUE DATE (IF PREGNANT) Calculating...
Your Fertility Forecast
NEXT OVULATION DATE Low Fertility
Calculating...
... days remaining
INTERACTIVE CYCLE LOG
Month YYYY
SuMoTuWeThFrSa
Period Days
Fertile Window
Ovulation Day
% Conception Chance
6-Month Cycle Forecast Log
Cycle Expected Period Fertile Window Ovulation Day

How does the Ovulation Calculator Predict Your Cycle?

This calculator uses standard clinical calculations based on the dates of your menstrual cycles. An average menstrual cycle length ranges from 21 to 35 days (often represented by a default of 28 days).

The calculation begins by estimating the start date of your Next Menstrual Period by adding the cycle length directly to the start date of your last period. The Ovulation Day occurs roughly 14 days prior to the start of the next cycle. That 14-day duration is known as the Luteal Phase. While standard calculators hardcode the luteal phase to 14 days, this calculator offers advanced range adjustments from 10 to 20 days for users who track their exact luteal phase duration through BBT charting or LH tests.

Understanding the 6-Day Fertile Window

Although ovulation is a single event where an egg is released and lives for only 12 to 24 hours, the Fertile Window spans approximately 6 days. This is because sperm can live inside the female reproductive tract for up to 5 days.

  • Medium/Low Fertility Days (Days -5 to -4): The start of the fertile window. Sperm viability exists but survival to the ovulation event is less likely.
  • High Fertility Days (Days -3 to -2): The middle phase of the window. Sperm introduced during these days has a strong survival chance to intercept the egg.
  • Peak Fertility Days (Days -1 to 0): The day before ovulation and the actual day of ovulation. This represents the peak likelihood of successful fertilization and conception.