Predict your fertile window, ovulation date, and next period — free, private, and instant.
| Cycle | Period Starts | Fertile Window | Ovulation | Next Period |
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Enter the first day of your last menstrual period, your typical cycle length (the number of days from the first day of one period to the first day of the next), and how many days your period typically lasts. Click Calculate My Cycle to instantly see your predicted ovulation date, fertile window, and upcoming cycle schedule for up to 12 months.
Understanding your menstrual cycle is one of the most practical things you can do for your reproductive health — whether you're actively trying to conceive, practicing natural family planning, or simply wanting to know your body better.
For couples trying to conceive, timing matters enormously. Sperm can survive inside the female reproductive tract for up to 5 days, and an egg is viable for only 12–24 hours after ovulation. That means your actual fertile window is roughly 6 days — the 5 days before ovulation plus the day of ovulation itself. Missing this window by even a day or two can mean waiting another full month.
For those using fertility awareness as birth control, tracking your cycle helps identify the days when pregnancy is most and least likely. And for anyone managing PMS, mood shifts, energy levels, or skin changes, knowing where you are in your cycle helps you plan workouts, social commitments, and self-care routines with much more intention.
The average cycle is 28 days, but anything from 21 to 45 days is considered within the normal range. Many women have naturally longer or shorter cycles — this calculator handles cycles anywhere in that range.
This calculator uses the standard luteal phase method, which assumes ovulation occurs approximately 14 days before the next expected period — not necessarily on day 14 of your cycle.
Ovulation Day = First Day of Last Period + (Cycle Length − 14)
Fertile Window = Ovulation Day − 5 days to Ovulation Day + 1 day
Next Period = First Day of Last Period + Cycle Length
For example, if your cycle is 32 days, ovulation is estimated at day 18 (32 − 14 = 18), not day 14. The cycle timeline is divided into four phases: menstrual (days 1 through your period length), follicular (period end to fertile window start), fertile/ovulation window (5 days pre-ovulation through ovulation), and the luteal phase (ovulation +1 through end of cycle).
This calculator provides estimates based on average cycle patterns. It's most accurate for women with regular cycles between 24 and 35 days. Women with irregular cycles (PCOS, perimenopause, post-hormonal-birth-control) may find the predictions less reliable. For greater accuracy, pair this with BBT tracking or OPK testing.
It's very unlikely but not impossible. Since ovulation can shift due to stress or illness, having unprotected sex outside the predicted fertile window carries a small risk. Sperm can survive up to 5 days, so intercourse several days before expected ovulation can still result in pregnancy if ovulation is delayed.
Cycle length naturally varies by a few days each month. Enter your average cycle length for the most useful predictions. If your cycle varies by more than 7–9 days regularly, you may have an irregular cycle — speak with a gynecologist or OB-GYN, as conditions like PCOS can cause significant variability.
It may take 1–3 months (sometimes longer) for your cycle to regulate after stopping hormonal contraceptives. During this transition, predictions will be less reliable. Start tracking once you've had 2–3 natural cycles and use the average of those to set your cycle length.