My period arrives four days earlier each month.

It’s quite common for menstrual cycles to vary slightly from month to month, and a consistent pattern of starting your period approximately four days earlier each cycle—while still falling within the typical range of 21 to 35 days—is generally considered normal. For example, if your average cycle length is 28 days but consistently shortens to 24 days, this reflects a regular, albeit shorter, cycle rather than true “early” menstruation. What matters most is consistency and predictability: if your cycles are reliably around 24 days, ovulation likely occurs about 10 days before menses (around day 14 of that cycle), and hormonal patterns remain intact.

Several physiological factors can contribute to this pattern, including natural interindividual variation in follicular phase duration, subtle shifts in luteinizing hormone (LH) surge timing, or mild fluctuations in stress, sleep, or metabolic demands—all of which may influence hypothalamic-pituitary-ovarian axis sensitivity without indicating pathology. However, if this change is new (i.e., previously stable 28-day cycles now consistently shortening), or if it’s accompanied by symptoms such as heavier bleeding, increased pain, irregular spotting, or difficulty conceiving, further evaluation is warranted. Potential considerations include thyroid dysfunction, elevated prolactin, emerging polycystic ovary syndrome (PCOS), or perimenopausal hormonal shifts—especially in individuals over age 40.

We recommend tracking your cycles for at least three to six months using a validated method (e.g., basal body temperature charting combined with cervical mucus observation or FDA-cleared fertility awareness apps). If your cycles remain consistently ~24 days and you’re asymptomatic, no intervention is typically needed. But if uncertainty persists—or if you’re planning pregnancy, managing contraception, or experiencing associated symptoms—consulting a gynecologist or reproductive endocrinologist for targeted assessment (e.g., mid-luteal serum progesterone, TSH, and AMH testing) can provide personalized clarity and reassurance.