What is a normal menstrual cycle length?

A normal menstrual cycle ranges from 21 to 35 days, with the average being 28 days. Periods typically last 2–7 days. Cycles vary naturally month to month by ±2–3 days. Significant variation (>7–10 days) or cycles consistently outside the 21–35 day range may warrant evaluation by a healthcare provider.

What are the 4 phases of the menstrual cycle?

The 4 phases: 1) Menstruation (Days 1–5): uterine lining shed; 2) Follicular phase (Days 1–13): FSH stimulates follicle growth, estrogen rises; 3) Ovulation (Day 14 in 28-day cycle): LH surge triggers egg release; 4) Luteal phase (Days 15–28): progesterone rises, prepares uterine lining. If no fertilization, progesterone drops and menstruation begins.

What causes irregular periods?

Common causes of irregular periods: significant weight changes (over or under), intense exercise or sudden increase in training, high stress levels, thyroid disorders, PCOS (polycystic ovary syndrome), perimenopause (age 40+), hormonal contraceptive use or changes, and certain medications. Occasional variation is normal; persistent irregularity warrants medical evaluation.

How do I calculate my next period?

Add your cycle length to the first day of your last period. For example: last period started March 1, cycle length 28 days → next period starts March 29. For irregular cycles, use your average cycle length calculated over the past 3–6 months. Most period tracking apps calculate this automatically using a rolling average.

Menstrual Cycle Calculator

Predict your next 6 periods, understand all 4 phases of your cycle, and track key dates including ovulation and fertile window. Personalized to your cycle length and period duration.

Your Cycle Overview

              Next Period Starts
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Days Until Next Period —

Current Cycle Phase —

Ovulation Date —

Your Cycle Phases (Current Cycle)

Next 6 Periods

#	Period Starts	Period Ends	Ovulation	Fertile Window

Cycle Phase Overview

Phase	Duration	Hormones	What's Happening
Menstruation	—	Low estrogen & progesterone	Uterine lining sheds; hormones at lowest point
Follicular	—	Rising estrogen (FSH)	Follicle matures; energy & mood often high
Ovulation	~1–2 days	LH surge, estrogen peak	Egg released; peak fertility window
Luteal	~14 days	Rising progesterone	Corpus luteum forms; PMS symptoms may appear

Understanding Your Menstrual Cycle

The menstrual cycle is controlled by a cascade of hormones: FSH (follicle-stimulating hormone), LH (luteinizing hormone), estrogen, and progesterone. These hormones interact in a precise feedback loop that repeats each cycle.

Why Track Your Cycle?

Family planning — identifying fertile and infertile days
Health monitoring — irregular cycles can indicate hormonal imbalances, PCOS, thyroid issues
Symptom patterns — PMS, migraines, or mood changes that correlate with cycle phase
Athletic performance — many women train differently across cycle phases; follicular phase often supports higher intensity

When to See a Doctor

Consult your healthcare provider if: cycles are consistently shorter than 21 days or longer than 35 days; periods are very heavy (soaking a pad/tampon every hour); severe pain (dysmenorrhea); bleeding between periods; or no period for 3+ months without pregnancy.

Frequently Asked Questions

A normal cycle ranges from 21 to 35 days, with the average being 28 days. Cycle length is counted from the first day of one period to the first day of the next. Occasional variation of a few days is normal. Cycles consistently shorter than 21 days or longer than 35 days, or significant variation month to month, may warrant a discussion with your healthcare provider.

Calendar-based prediction estimates ovulation at approximately 14 days before your next expected period. This works best with regular cycles — irregular cycles make calendar prediction unreliable. For more accurate ovulation tracking, use ovulation predictor kits (OPKs) or basal body temperature (BBT) charting alongside calendar estimates.

Common causes include stress, significant weight change, intense exercise, PCOS (polycystic ovary syndrome), thyroid disorders, and perimenopause. Hormonal birth control suppresses natural cycles. Pregnancy always stops menstruation. If your cycles are consistently irregular or have changed significantly, a healthcare provider evaluation is recommended.

The menstrual cycle has four phases: Menstruation (days 1–5): uterine lining sheds. Follicular phase (days 1–13): estrogen rises, follicles develop. Ovulation (around day 14 in a 28-day cycle): an egg is released. Luteal phase (days 15–28): progesterone rises, preparing the uterus. If no pregnancy occurs, progesterone drops and menstruation begins the next cycle.

Most periods last 3–7 days, with the heaviest flow typically in the first 2 days. Periods shorter than 2 days or longer than 7 days may warrant medical evaluation. Average blood loss per period is 30–80 mL (about 2–6 tablespoons). Soaking through a pad or tampon every hour for several hours is considered heavy bleeding and should be discussed with a healthcare provider.

Yes. Psychological or physical stress triggers cortisol release, which can disrupt the hormonal cascade needed for ovulation. Elevated cortisol interferes with GnRH pulsing, which delays or prevents the LH surge needed to trigger ovulation. A delayed or missed ovulation shifts the entire cycle, causing a late period. Once stress resolves, cycles typically return to normal within 1–2 months.