lunarlog

Cycle Length & Natural Variation: What Is "Normal"?

Why cycles fluctuate naturally, how adolescent and adult variations differ, and what variation means for health.

Cycle literacy - Cycle Patterns & Health, about 3 min read

The Myth of the 28-Day Clockwork Cycle

Only a small fraction of individuals have exactly 28-day cycles every month. In healthy adults, the gap between the shortest and longest cycle is usually up to about 7 to 9 days, depending on age.

Factors such as psychological stress, travel, illness, shifts in sleep schedule, and vigorous exercise can transiently delay follicular development and shift ovulation date, extending that month's cycle.

The First Few Years

For the first two to three years after a first period, cycles are often longer and less predictable — most fall between about 21 and 45 days. An occasional longer cycle can happen, but if periods come more than 45 days apart, or you go 3 months (90 days) without one, check in with a doctor.

Once cycles have settled, an adult cycle generally falls between about 21 and 35 days, and a few days of month-to-month variation remains normal.

When to Ask a Doctor

Check in with a healthcare professional if: you go 3 months (90 days) without a period — even if your cycles were never regular; bleeding lasts more than 7 days; you need to change a soaked pad or tampon every 1 to 2 hours; or you pass clots the size of a quarter (about 2.5 cm) or bigger. If you've had sex and your period is late, take a pregnancy test. Get help right away if you feel dizzy or light-headed, or your heart is racing, while you're bleeding.

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