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Open Tool →Ovulation Calculator
Enter the date of your last period and your average cycle length to predict your ovulation date, fertile window, and when your next period is due.
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This calculator provides estimates based on average cycle patterns. It is intended for informational purposes only and should not be used as a contraceptive method or to diagnose a medical condition. Ovulation timing varies by person and cycle. Consult your GP or gynaecologist for personal medical advice.
Typical range: 21–45 days
Typical range: 10–16 days
Predicted Ovulation Date
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—Fertile window starts
—Fertile window ends
—Next period due
—Days until ovulation
Your cycle overview
The fertile window is the 5 days before ovulation plus the ovulation day itself. Sperm can survive up to 5 days in the reproductive tract, so intercourse before ovulation can still result in pregnancy.
⚠️ Results are estimates. Stress, illness, or lifestyle changes can shift ovulation timing significantly.
Ovulation Calculator — Understanding Your Fertile Window
Ovulation is the release of a mature egg from the ovary, which then travels down the fallopian tube where it can be fertilised by sperm. For most people with a regular menstrual cycle, ovulation occurs approximately 12–16 days before the next period is due — not necessarily at the midpoint of the cycle as is commonly assumed.
How the Calculator Works
This ovulation calculator uses two key inputs: the first day of your last menstrual period (LMP) and your average number of days between periods. It then subtracts the typical luteal phase length (the time from ovulation to the next period) from your total cycle length to estimate the day you ovulate. For a standard 28-day cycle with a 14-day luteal phase, ovulation would fall on day 14.
What is the Fertile Window?
The fertile window refers to the days in a cycle when pregnancy is possible. Because sperm can survive inside the female reproductive tract for up to 5 days, the fertile window spans approximately 6 days: the 5 days prior to ovulation and the day of ovulation itself. The egg, however, can only be fertilised for about 12–24 hours after it is released. This means that timing intercourse in the days leading up to ovulation — rather than on ovulation day itself — often gives the best chance of conception.
Irregular Cycles and Ovulation Tracking
If your cycle length varies significantly from month to month, calendar-based ovulation prediction becomes less reliable. Signs of ovulation include a change in cervical mucus (becoming clear, slippery, and egg-white in consistency), a subtle rise in basal body temperature (BBT), and sometimes mild one-sided pelvic discomfort known as mittelschmerz. Ovulation predictor kits (OPKs) measure the surge in luteinising hormone (LH) that occurs 24–36 hours before ovulation and are considerably more accurate than calendar methods.
A Note on Contraception
Calendar-based awareness of your cycle is not a reliable contraceptive method. Ovulation timing can shift due to stress, illness, travel, significant weight changes, and many other factors. If you are not trying to conceive, please use a medically proven contraceptive method and consult a healthcare provider for guidance.