Menstrual Cycle Tracker
Period
Calculator
Predict your next 6 periods, ovulation dates, PMS window, and safe days. View a 6-month color-coded calendar and check if your period is late.
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Next Period
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Next Ovulation
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Days Away
Your Cycle Details
days
📊 Current Cycle Position
Day 1Day 14Day 28
Day — of your cycle
Enter your LMP to see current phase
Next Period
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Next Ovulation
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PMS Window
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Safe Days Est.
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How to Calculate Your Next Period
A period calculator predicts your next menstrual cycle start date by adding your average cycle length to the first day of your last period. Cycle length is the number of days from the first day of one period to the first day of the next — not the number of days of bleeding.
Understanding Your Cycle Phases
Next Period = Last Period Start + Cycle Length
Ovulation Day = Last Period Start + (Cycle Length − Luteal Phase)
Fertile Window = Ovulation − 5 days to Ovulation + 1 day
PMS Window = Period Start − 7 to − 3 days (premenstrual)
Safe Days (est.) = Days 1–7 and days after ovulation + 3
Note: "Safe days" is NOT reliable contraception — cycles vary.
Why Periods Can Be Irregular
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Stress
High cortisol suppresses GnRH, delaying the LH surge and pushing ovulation later — extending your cycle.
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Weight Changes
Significant weight loss or gain disrupts estrogen balance, leading to missed or irregular periods.
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Intense Exercise
Very high training loads can suppress the HPO axis, causing exercise-induced amenorrhea (no periods).
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PCOS & Thyroid
PCOS causes irregular ovulation; thyroid disorders affect cycle regularity and flow. Both are treatable.
Frequently Asked Questions
What is a normal menstrual cycle length?
A normal menstrual cycle is between 21 and 35 days, with 28 days being the textbook average. Cycle length varies between women and can vary month-to-month in the same woman. Variations of 7–9 days between your shortest and longest cycle are normal. Cycles consistently shorter than 21 days or longer than 35 days may warrant evaluation by a gynecologist.
When does PMS (premenstrual syndrome) start?
PMS symptoms typically begin 7–14 days before menstruation (during the late luteal phase) and resolve within a few days of the period starting. Common symptoms include mood changes, bloating, breast tenderness, food cravings, and fatigue. PMDD (premenstrual dysphoric disorder) is a severe form requiring medical treatment. Tracking your cycle helps identify your personal PMS pattern.
How many days late is considered a missed period?
A period is typically considered missed if it's more than 5–7 days past the expected start date. One missed period is not unusual and can be caused by stress, illness, travel, or hormonal fluctuations. If your period is 7+ days late and you're sexually active, a pregnancy test is recommended. If you're not pregnant and continue missing periods (oligomenorrhea) or have no periods for 3+ months (amenorrhea), consult a healthcare provider.
How much does cycle length vary from month to month?
Research shows that most women's cycles vary by 2–7 days from month to month, with variations being more common in the follicular phase (before ovulation) than in the luteal phase (after ovulation). The luteal phase is typically stable at 12–16 days. Using cycle-tracking apps over 3–6 months gives a more accurate average cycle length for prediction.
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