Tool
Ovulation Calculator
Estimate your likely ovulation day and fertile window from the first day of your last period and your usual cycle length.
Enter the date of your last period and your cycle length to see an estimate.
This is an estimate based on average cycle timing, not a measurement of ovulation. It becomes unreliable if your cycles are irregular, since the calculation assumes a consistent cycle length. If your cycles are irregular, or you have a known diagnosis such as PCOS, ovulation tracking by ultrasound is more reliable than a date-based estimate. If you have been trying to conceive for 12 months, or 6 months if you are over 35, without success, see our page on infertility evaluation and treatment.
Context
Why this is an estimate, not a diagnosis
This calculator assumes ovulation occurs roughly 14 days before the next period, which holds reasonably well for regular cycles but not for irregular ones. Cycle length can vary from month to month for many reasons, including stress, illness and hormonal conditions. If you are timing intercourse around this estimate and have not conceived within a reasonable period, or if your cycles are unpredictable, book a consultation rather than continuing to guess from the calendar.
Cycles that do not fit a calendar deserve a proper look
If your periods are irregular or unpredictable, ovulation tracking by ultrasound gives a real answer.
Monday to Sunday, 09:30 to 18:30