For most people asking this question, “one cycle of phases” means the menstrual cycle. That full cycle of phases is usually about 28 days, but anything from about 21 to 35 days is considered normal for adults.

What “one cycle of phases” means

  • The menstrual cycle is counted from the first day of one period to the day before the next period starts.
  • In that time, the body moves through four main phases: menstrual, follicular, ovulation, and luteal.

If you were instead asking about the Moon’s phases, one full cycle of lunar phases (new moon back to new moon) is about 29.5 days, which is called a lunation.

Typical menstrual cycle length

  • Average length: around 28 days.
  • Normal adult range: roughly 21–35 days, with some natural variation from month to month.
  • Teen cycles can be a bit longer or more irregular at first, then usually settle into a more consistent pattern over time.

Quick phase rundown (menstrual cycle)

  • Menstrual phase: bleeding, usually about 3–7 days.
  • Follicular phase: starts with your period and continues until ovulation; often 14–21 days in total.
  • Ovulation phase: release of an egg, a short window in the middle of the cycle.
  • Luteal phase: from ovulation until the next period, commonly about 12–14 days.

If you meant the Moon instead

  • A full set of Moon phases (new → first quarter → full → last quarter → back to new) is one lunar cycle.
  • That cycle is about 29.5 days long.

TL;DR:

  • Menstrual cycle phases: usually ~28 days total (often 21–35 days).
  • Moon phase cycle: about 29.5 days.

If you tell what kind of “phases” you mean (period, Moon, something else?), a more tailored breakdown can be given.