Free Period Calculator Online
Predict your next 6 periods with this free period calculator. Enter your last period start date, cycle length, and period duration to get ovulation dates and fertile windows — all free and online.
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Understanding Your Menstrual Cycle
The menstrual cycle has four phases: menstruation (your period), the follicular phase, ovulation, and the luteal phase. This period calculator tracks the full cycle so you can anticipate each phase. The average cycle is 28 days, but anything from 21 to 35 days is considered normal.
During the follicular phase, follicle-stimulating hormone (FSH) triggers egg development. Ovulation releases the mature egg around mid-cycle. The luteal phase follows, lasting about 14 days regardless of total cycle length. If pregnancy does not occur, hormone levels drop and the uterine lining sheds — your period begins again.
The period calculator assumes a consistent cycle length to project future periods. If your cycles vary significantly, the predictions become less precise — but the calculator still gives you a useful baseline for planning.
Cycle Phases Explained
Menstruation (Days 1–5)
The uterine lining sheds, causing bleeding for 3–7 days. Hormone levels are at their lowest. This is day 1 of your cycle — the date you enter in the period calculator.
Follicular Phase (Days 6–13)
Rising estrogen thickens the uterine lining. One egg matures in a follicle. Energy and mood typically improve during this phase.
Ovulation (Day 14)
The mature egg releases from the ovary. This is the most fertile day. The period calculator marks this date for each predicted cycle.
Luteal Phase (Days 15–28)
Progesterone rises to maintain the uterine lining. PMS symptoms may appear in the final week. If no pregnancy occurs, hormone levels drop and the next period begins.
When to See a Doctor About Your Period
Track your cycles with this free period calculator and share the data with your provider if you notice irregularities. See a doctor if your period consistently lasts more than 7 days, you soak through a pad or tampon every hour, your cycles are shorter than 21 days or longer than 35 days, you miss 3 or more periods in a row (without pregnancy), or you experience severe cramps that interfere with daily life. Period tracking data from this online calculator can help your doctor identify patterns and diagnose conditions like PCOS, endometriosis, or thyroid disorders more quickly.
Frequently Asked Questions
Disclaimer: This free online period calculator provides estimates based on average cycle patterns. It is not a contraceptive tool and should not be used to prevent pregnancy. Consult a healthcare provider for medical advice regarding your menstrual health.
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