Estimate your ovulation date and most fertile days from your last period.
Calculated privately in your browser.
How do you calculate your ovulation date?
Ovulation is estimated about 14 days before your next period (cycle length − 14), with the fertile window spanning roughly 5 days before to 1 day after ovulation. For example, with a 28-day cycle starting 1 June, ovulation is around 15 June and the fertile window runs about 10–16 June. This is an estimate for regular cycles; timing varies.
Understanding your result
This is an estimate for regular cycles. Ovulation timing varies, so ovulation tests or tracking are more precise.
Formula and method
Ovulation is estimated about 14 days before your next period (cycle length − 14). The fertile window spans roughly 5 days before to 1 day after ovulation.
Assumptions and limitations
This is a general estimate for regular cycles, not medical advice, and timing varies between individuals and from cycle to cycle. It cannot detect actual ovulation, so it should not be relied on for avoiding or achieving pregnancy. Ovulation tests or clinical tracking are more precise, and a healthcare professional can give personal guidance.
Worked example
With a 28-day cycle starting 1 June, ovulation is around 15 June and the fertile window runs about 10–16 June.
How to use this tool
- Enter the first day of your last period.
- Set your average cycle length.
- Press Calculate.
About the Ovulation Calculator
The Ovulation Calculator estimates when you ovulate and your most fertile days, based on your last period and cycle length.
Who should use this tool
People tracking their menstrual cycle who want an estimate of their likely ovulation date and fertile window from their last period and cycle length. Useful for general awareness and planning, particularly for those with reasonably regular cycles who want a starting point rather than a precise reading.
Benefits
- Estimates your ovulation date from cycle length and last period
- Shows an approximate fertile window around ovulation
- Gives a simple starting point for cycle awareness
- Calculates privately in your browser with no account
Practical use cases
- Getting a rough idea of your likely fertile days
- Planning around an estimated ovulation date
- Understanding how cycle length shifts the estimate
- Complementing ovulation tests with a predicted window
Explore all Health and Nutrition tools
Frequently asked questions
How accurate is this?
It’s a calendar estimate best suited to regular cycles. For accuracy, combine it with ovulation predictor kits or symptom tracking.
How is the fertile window estimated?
The tool places estimated ovulation about fourteen days before your next expected period, based on your cycle length. It then marks a window spanning roughly the five days before ovulation to one day after. This reflects the general period around ovulation, though the exact timing varies between people and cycles.
What if my cycles are irregular?
The estimate assumes a fairly regular cycle, so irregular cycles make the predicted dates less reliable. If your cycle length varies noticeably, the tool can only give a rough guide. Ovulation tests, symptom tracking or advice from a healthcare professional offer a more accurate picture in that situation.