How do menstrual cycles work?

The menstrual cycle is the monthly pattern of brain–ovary–uterus signaling that prepares the body for possible pregnancy and resets through menstruation when pregnancy does not occur ^[1]. For people tracking premenstrual dysphoric disorder (PMDD) or related premenstrual symptoms, knowing phase names and how they relate to bleeding and ovulation helps interpret when symptoms tend to build and ease—without replacing clinical assessment (see the companion article What is PMDD? for diagnostic context).

Skim tip: If you are low on energy, jump ahead to Why the luteal phase matters for PMDD for how cycle timing connects to PMDD symptoms.

The four phases

Clinicians and educators often describe four phases: menstrual (bleeding), follicular (before ovulation), ovulation, and luteal (after ovulation until the next period).

• Menstrual and early follicular phase. Cycle day 1 is the first day of menstrual bleeding, and the follicular phase starts then too—so the bleeding days and the pre-ovulation buildup share the same starting point on the calendar. If no pregnancy occurs, estrogen and progesterone fall, the uterine lining sheds, and menstrual bleeding happens ^[2].
• Ovulation. The pituitary gland increases follicle-stimulating hormone (FSH), which stimulates ovarian follicles to mature; rising estrogen from the dominant follicle leads to a luteinizing hormone (LH) surge, and a mature egg is released from the ovary ^[3].
• Luteal phase (after ovulation). The empty follicle becomes the corpus luteum; estrogen and progesterone rise and then fall sharply to trigger the next menses if fertilization does not occur ^[4].

Four-phase diagrams assume a typical ovulatory cycle. Hormonal contraception, anovulatory cycles, polycystic ovary syndrome (PCOS), amenorrhea, and perimenopause can suppress or change ovulation, so phase labels and timing may not match a textbook chart.

For how ovaries, uterus, and related structures fit into each phase, see Reproductive Anatomy and PMDD. For plasma-level detail on how hormones rise and fall, see Plasma hormones during cycle; this article stays focused on phase names and timing.

Hormones across the cycle

Reproductive hormones do not move in a single fixed pattern for everyone, but several hormones rise and fall in a coordinated sequence across the phases above. FSH and LH from the pituitary help regulate follicle growth and ovulation ^[5]. Estrogen rises through the follicular phase and peaks near ovulation; progesterone stays relatively low until after ovulation, when levels from the corpus luteum increase through the luteal phase. Research mapping neuroactive steroids—brain-active substances made from hormones—shows that allopregnanolone, a calming compound formed from progesterone, generally follows a cycle shape similar to progesterone, with the clearest differences from other parts of the cycle in the mid-luteal portion ^[6]. Many cycle charts—including visual summaries in health apps—plot estrogen, progesterone, LH, and FSH across the month as a learning tool.

Why the luteal phase matters for PMDD

For many people with PMDD, the hardest stretch is the luteal phase—from ovulation until the next period—when mood, thinking, and physical symptoms often build in step with normal ovarian hormone shifts ^[7]. In frameworks used for PMDD, distressing symptoms are often worst in the week before a period, improve as bleeding starts, and reflect sensitivity to normal cyclical hormone changes rather than a fixed high or low hormone level on a lab test; people whose symptoms do not ease in the follicular phase may be evaluated for premenstrual exacerbation (PME)—cyclical worsening of another underlying condition—rather than PMDD alone ^[8]. That luteal concentration is typical for many people with PMDD, but timing is not uniform—a 2025 conference abstract on prospective daily ratings reported large variability in when symptoms peak, including mainly perimenstrual increases and exploratory subgroups with late symptom offset or symptoms persisting through much of the luteal phase ^[9]. Research summarized in recent frameworks also describes hypothesized, candidate timing patterns—such as luteal-onset, perimenstrual-onset, and periovulatory-onset forms of hormone-linked mood change—so symptom windows can differ between individuals ^[10]. Cyclical mood changes tied to the cycle are a physiological pattern—not a character flaw—and accurate timing notes can support conversations with a qualified clinician.

Cycle length and individual variation

Cycle length and the timing of ovulation vary from person to person and from month to month. Reviews commonly cite 21–35 days as a typical range for a normal cycle length, with about 28 days often used as a textbook average ^[11]. Ovulation does not always occur at the mathematical midpoint of every cycle; the follicular phase tends to vary more in length than the luteal phase, so counting fixed “cycle days” from bleeding alone can misalign hormone changes between people ^[12]. Irregular cycles are also common at menarche and before menopause, when length may be longer or shorter than average ^[13]. In population studies using prospective diaries, many menstruating people show some symptom change between follicular and luteal phases even when they do not meet PMDD criteria—underscoring that cyclical bodily shifts can be common while PMDD is defined by severity and impairment ^[14]. A pattern that differs from a generic 28-day diagram is not automatically a problem; persistent, troubling irregularity is worth discussing with a healthcare provider.

Using cycle knowledge with PMDD

Logging cycle phase alongside mood and physical symptoms can help spot patterns and plan for harder days, but tracking alone does not diagnose PMDD. Diagnostic criteria call for prospective daily symptom ratings across at least two symptomatic menstrual cycles; tools such as the Daily Record of Severity of Problems (DRSP) support standardized mood-and-cycle tracking for that purpose ^[15]. Despite this, prospective tracking is often not used in routine clinical care because of time limits, training gaps, and the burden of manual diaries ^[16]. When period apps assume rigid cycle lengths or label ovulation in ways that do not match an irregular cycle, some users report distress or feeling “abnormal”—a reminder that flexible, individualized tracking matters ^[17]. Bringing whatever records you have to a qualified clinician supports assessment and care planning; cyclical symptoms deserve serious attention, and they are not a sign of weak willpower.