Ovulation Calculator - Estimate Your Fertile Window Free Ovulation Calculator
Enter the first day of your last period and your average cycle length to estimate your ovulation date, fertile window and next period date for the upcoming months.
Period Details
Ovulation Estimate
Cycle-by-Cycle Forecast
| Cycle | Ovulation | Fertile Window | Next Period |
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Ovulation Calculator - Guide
What is Ovulation?
Ovulation is the release of a mature egg from the ovary, which typically occurs once per menstrual cycle. The egg travels through the fallopian tube where it can be fertilised by sperm. Understanding when ovulation occurs helps with family planning — whether trying to conceive or avoid pregnancy.
How is Ovulation Date Calculated?
Ovulation Day = Next Period Date − 14 days
The luteal phase (time from ovulation to next period) is typically 14 days. The calculator uses this to work backwards from the expected next period date.
Example (28-day cycle):
- Last period = January 1
- Next period = January 29
- Ovulation = January 29 − 14 = January 15
- Fertile window = January 10 – January 15
The Fertile Window
The fertile window spans approximately 6 days: the 5 days before ovulation and the day of ovulation itself. This is because sperm can survive in the female reproductive tract for up to 5 days, while the released egg is viable for only 12–24 hours.
Signs of Ovulation
- Basal Body Temperature: A slight rise (0.2–0.5°C) after ovulation.
- Cervical Mucus: Becomes clear, stretchy and slippery (egg-white consistency).
- Mild Pelvic Pain: Some women feel a twinge on one side (mittelschmerz).
- LH Surge: Ovulation predictor kits detect the luteinising hormone surge 24–36 hours before ovulation.
Disclaimer
This calculator provides estimates based on average cycle data and should not be relied upon as a method of contraception. Actual ovulation timing can vary. Consult a healthcare professional for personalised fertility advice.