A woman’s menstrual cycle has four distinct stages: menstruation, the follicular phase, ovulation, and the luteal phase. A full cycle averages 28 days but anywhere from 21 to 35 days is considered normal. Each stage is driven by shifting hormone levels that prepare the body for a potential pregnancy, then reset if one doesn’t occur.
Menstruation (Days 1 to 7)
The cycle begins on the first day of your period. This is the shedding of the uterine lining that built up during the previous cycle. Bleeding typically lasts 2 to 7 days, and the total blood loss over the entire period is usually around 60 milliliters, or roughly 2.7 ounces. Losing more than 80 milliliters regularly is considered heavy bleeding and worth bringing up with a provider.
Hormone levels are at their lowest point during menstruation. Progesterone, the hormone that was holding the uterine lining in place, has dropped sharply. That withdrawal is what triggers the lining to break down. At the same time, the brain begins releasing more follicle-stimulating hormone (FSH) to kick off the next round of egg development, which means the next phase is already underway before your period ends.
The Follicular Phase (Days 1 to 13)
The follicular phase overlaps with menstruation and continues after bleeding stops. It’s named for the follicles, small fluid-filled sacs in the ovaries that each contain an immature egg. Rising FSH stimulates several of these follicles to start growing, but eventually one dominant follicle pulls ahead. The others stop developing.
As that dominant follicle grows, it produces increasing amounts of estrogen. This rising estrogen does two important things: it signals the uterus to start rebuilding its lining (thicker, blood-rich tissue that could support a pregnancy), and it tells the brain to dial back FSH production since a lead follicle has already been selected. Estrogen climbs steadily through the mid-follicular phase, peaking just before ovulation.
During the early part of this phase, cervical mucus is dry or sticky and paste-like, often white or slightly yellow. As estrogen rises in the days approaching ovulation, the mucus gradually becomes creamier, then watery, and finally stretchy and slippery, resembling raw egg whites. That egg-white consistency around days 10 to 14 is a reliable sign that your most fertile days have arrived.
Ovulation (Around Day 14)
Ovulation is the shortest phase, lasting roughly 24 hours. It’s triggered by a sharp spike in luteinizing hormone (LH), often called the LH surge. That surge begins about 34 to 36 hours before the egg is actually released, and the LH peak occurs about 10 to 12 hours before ovulation. This is the window that at-home ovulation test kits are designed to detect.
When LH peaks, the dominant follicle ruptures and releases a mature egg into the fallopian tube. Once released, the egg is viable for only about 24 hours. Sperm, however, can survive inside the reproductive tract for up to 5 days. This is why the fertile window is wider than ovulation itself. The highest pregnancy rates occur when sperm meets the egg within 4 to 6 hours of ovulation, but conception is possible from intercourse that happened several days earlier if sperm were already waiting in the fallopian tube.
Some women feel a twinge of pain on one side of the lower abdomen during ovulation, sometimes called mittelschmerz. Your basal body temperature also shifts slightly after ovulation, rising by less than half a degree Fahrenheit (about 0.3°C). If that small temperature bump holds steady for three or more days, ovulation has likely occurred. The key detail: the temperature rise confirms ovulation after the fact, so it’s more useful for understanding your pattern over several cycles than for predicting fertility in real time.
The Luteal Phase (Days 15 to 28)
After the egg is released, the empty follicle transforms into a temporary structure called the corpus luteum. This structure pumps out progesterone, which is now the dominant hormone. Progesterone’s main job is maintaining and enriching the uterine lining so it’s ready for a fertilized egg to implant. The uterus enters what’s called the secretory phase: the lining thickens further, develops new blood vessels, and produces nutrients.
Estrogen also rises a second time during this phase, reaching a secondary peak around the middle of the luteal phase. Peak progesterone and estrogen levels occur roughly 8 to 9 days after ovulation, which coincides with when a fertilized egg would typically implant.
If the egg isn’t fertilized, the corpus luteum begins to break down after about 10 to 14 days. Progesterone and estrogen drop, the blood supply to the uterine lining decreases, and the lining starts to shed. That brings you back to day 1: menstruation.
The luteal phase is the most consistent part of the cycle. It’s almost always between 12 and 14 days long, regardless of your total cycle length. Variation in cycle length is mostly driven by the follicular phase, which can be shorter or longer depending on how quickly a dominant follicle develops.
How Hormones Drive the Entire Cycle
Four hormones orchestrate everything: FSH, LH, estrogen, and progesterone. They work in a feedback loop. FSH rises when estrogen and progesterone are low (during menstruation), prompting follicle growth. The growing follicle produces estrogen, which eventually suppresses FSH and triggers the LH surge. Ovulation follows. The corpus luteum then produces progesterone, which holds the lining steady until either pregnancy begins or the corpus luteum breaks down, restarting the cycle.
Estrogen effectively rises and falls twice per cycle: once during the follicular phase leading up to ovulation, and once during the mid-luteal phase. This double peak explains why some women notice mood or energy shifts at two different points in their cycle rather than just one.
Tracking Your Cycle With Physical Signs
You don’t need bloodwork to get a rough sense of where you are in your cycle. Three observable signs change predictably:
- Cervical mucus: Progresses from dry or sticky after your period, to creamy and white, to wet and watery, to stretchy and egg-white-like at peak fertility. After ovulation, it dries up again until your next period.
- Basal body temperature: Stays lower during the follicular phase, then rises slightly (less than 0.5°F) after ovulation and remains elevated through the luteal phase. Tracking this daily with a thermometer before getting out of bed can confirm ovulation patterns over time.
- Period timing: Since the luteal phase is nearly always 12 to 14 days, counting backward from the start of your period can help estimate when you ovulated. If your cycle is 30 days, ovulation likely happened around day 16 or 17, not day 14.
What Affects Cycle Length
A cycle anywhere from 21 to 35 days is normal, and your own cycle can vary by a few days from month to month. The follicular phase is the main source of that variation. Stress, illness, significant weight changes, intense exercise, and hormonal conditions like polycystic ovary syndrome can all delay or speed up follicle development, shifting when ovulation happens and therefore how long the full cycle lasts.
Consistently short cycles (under 21 days) or long cycles (over 35 days) may signal that ovulation isn’t occurring regularly. Irregular cycles are common during the first few years of menstruation and again in the years approaching menopause, but persistent irregularity outside those transitions is worth investigating.