Period Tracker & Next Period Calculator

How Menstrual Cycles Work The menstrual cycle is counted from day 1 of one period to day 1 of the next. The average cycle length is 28 days, but a normal range is 21–35 days. The cycle has two phases: the follicular phase (day 1 to ovulation) and the luteal phase (ovulation to next period). The luteal phase is typically 14 days and is relatively consistent. The follicular phase varies in length.

Predicting Your Next Period Next period start = Last period start + Cycle length. For example: if your last period was April 1 and your cycle is 28 days, your next period begins around April 29. This is a statistical estimate — actual timing can vary by a few days based on stress, illness, travel, and other factors.

Ovulation and the Fertile Window Ovulation typically occurs 14 days before the next period (day 14 in a 28-day cycle, day 18 in a 32-day cycle). The egg survives 12–24 hours after release. Sperm survive 3–5 days in the female reproductive tract. The fertile window spans approximately 5 days before ovulation plus ovulation day itself — about 6 days total. The peak fertility days are the 2 days before ovulation and ovulation day itself.

Cycle Variations Irregular cycles: if your cycles vary by more than 7–9 days month to month, tracking ovulation by calendar alone is unreliable. Short cycles (under 21 days): periods may overlap with the fertile window. Long cycles (over 35 days): ovulation is delayed and less predictable. Anovulatory cycles: some cycles occur without ovulation — common during stress, illness, or hormonal transitions. Tracking methods: basal body temperature (BBT) rises 0.2–0.5°C after ovulation. Cervical mucus becomes clear and stretchy near ovulation.

Premenstrual Syndrome (PMS) Symptoms like bloating, mood changes, cramps, and fatigue typically begin 1–2 weeks before a period (the luteal phase). Severe PMS is called Premenstrual Dysphoric Disorder (PMDD) and affects 3–8% of women of reproductive age.

When to See a Doctor Cycles shorter than 21 days or longer than 35 days consistently. Periods lasting more than 7 days or with unusually heavy flow. Severe pain not relieved by over-the-counter pain medication. Cycles that suddenly change significantly from your normal pattern. Missing 3 or more periods without a known cause (pregnancy, menopause, medication).

Note on Calendar-Only Methods Calendar-based cycle tracking is for awareness, not contraception. As a contraceptive method alone, it has a 24% failure rate with typical use. Always consult a healthcare provider for family planning advice.