Free Online Ovulation & Period Calculator
Predict fertile days, ovulation, and upcoming periods.
The luteal phase is the time between ovulation and your next period. It is usually 12–16 days and stays fairly constant for each person.
Ovulation predictions are estimates, not contraception. Cycles can shift with stress, illness, travel, and hormonal changes. Use this tool for planning and discussion with a healthcare provider.
Next six cycles
| Cycle | Period starts | Estimated ovulation | Fertile window |
|---|
About the Ovulation & Period Calculator
Ovulation is the release of an egg from the ovary, usually about midway through the menstrual cycle. Knowing when it is likely to happen helps with conception planning and with understanding your cycle. This calculator uses the first day of your last period, your average cycle length, and your luteal phase to estimate ovulation, the fertile window, and the dates of your next periods.
How the prediction works
The luteal phase is the second half of the cycle, from ovulation to the start of the next period. It is usually around 14 days and changes less from month to month than the first half. The calculator subtracts your luteal phase from your cycle length to locate ovulation, then counts back five days and forward one day to mark the fertile window. Sperm can survive for several days, so the days before ovulation matter as much as ovulation day itself.
The table extends the same pattern six cycles ahead, assuming the same cycle length each month. Real cycles rarely repeat with perfect regularity. A variation of a few days is normal; a consistently short or long cycle, or a cycle that changes abruptly, is worth discussing with a healthcare professional.
Frequently asked questions
Can I use this to avoid pregnancy?
No. Calendar-based predictions alone are not a reliable contraceptive method because ovulation timing can shift unpredictably. Use a method recommended by a healthcare provider.
What if my cycle is irregular?
Average-length predictions are less reliable when cycles vary. Tracking basal body temperature, cervical mucus, and ovulation tests can give a better picture, and a clinician can help investigate persistent irregularity.
Does ovulation always happen on day 14?
No. Day 14 is a convenient average for a 28-day cycle. Ovulation timing depends on the length of the first half of your cycle, which is why this calculator uses your own cycle length and luteal phase.