Understanding Your Menstrual Cycle

A menstrual cycle is counted from the first day of one period to the first day of the next, and while 28 days gets cited as "average," anywhere from 21 to 45 days can be typical depending on the person. The cycle has four phases, each driven by a different hormonal change.

Menstrual phase

This is when bleeding occurs, typically lasting three to seven days. It ends the previous cycle and starts the new one, as the uterine lining that built up in case of pregnancy is shed.

Follicular phase

Overlapping with menstruation and continuing after it, the follicular phase is when the pituitary gland signals the ovaries to prepare an egg. Estrogen rises, the uterine lining starts rebuilding, and energy levels often climb.

Ovulation

Around the midpoint of a typical cycle, a surge in luteinizing hormone triggers the release of a mature egg. This is the single most fertile day of the cycle, though the days before it matter just as much, because sperm can survive for several days waiting for an egg.

Luteal phase

After ovulation, progesterone rises to help maintain a potential pregnancy. If the egg isn't fertilized, hormone levels drop toward the end of this phase, which triggers the next period and starts the cycle over. The luteal phase is usually more consistent in length than the rest of the cycle, commonly around 12 to 14 days, which makes it useful for predicting your next period.

Tracking your cycle over a few months can help you notice your own patterns. OurPeriod & Ovulation Tracker uses your average cycle and luteal phase length to estimate these phases for you.