The menstrual cycle phases are four: the period, the follicular phase that builds towards ovulation, ovulation itself, and the luteal phase that ends when the next period begins. Each is run by a different hormone, each changes how you feel, and the whole cycle is easier to read once the dates are on a calendar. The five tools below map a cycle from one date and a cycle length, find the fertile window, and take over when a cycle turns into a pregnancy. Under them is each phase day by day, what shifts in the years before menopause, and every guide in this site’s hormones section.
Pregnancy, Fertility & Family
The Four Phases, Day by Day
Day one is the first day of bleeding, and the cycle runs to the day before the next period starts. The average cycle is 28 days and anything from 21 to about 35 days is normal for an adult; a period lasts three to seven days. The days below are for a 28-day cycle. With a longer or shorter cycle, the first half stretches or shrinks and the second half stays close to two weeks, which is the single most useful thing to know about your own timing.
| Phase | Days (28-day cycle) | What rises | What happens |
|---|---|---|---|
| Menstrual | 1 to about 5 | Nothing yet: estrogen and progesterone are at their lowest | The uterine lining sheds. Energy is often lowest here and iron leaves with the blood |
| Follicular | 1 to 13, overlapping the period | Follicle-stimulating hormone, then estrogen | Follicles grow in the ovary and one egg matures; the lining rebuilds; mood and energy tend to climb with estrogen |
| Ovulation | About day 14, or 14 days before the next period | A surge of luteinising hormone | The egg is released and lives 12 to 24 hours; the fertile window is the five days before plus this one |
| Luteal | About 15 to 28 | Progesterone | The lining thickens to receive an egg; if none arrives, both hormones fall in the last days and the period follows |
The period tool takes one start date and your average length and lays out the next six cycles, each period and each ovulation day; the ovulation tool narrows in on the fertile window for the next four. Both are calendar arithmetic, and the calendar is only as regular as the cycle it is fed: stress, travel, illness, heavy training and a change in weight all delay ovulation, and every day ovulation moves, the period after it moves too.
Living With the Phases
Most of what people notice from week to week is the second half of the cycle. Progesterone in the luteal phase raises body temperature and appetite a little, holds fluid, and in the last days its fall with estrogen brings the low mood, cramps and bloating grouped as PMS. None of that needs a special diet, but some things help in a predictable way: iron-rich food around a heavy period, because iron leaves with the blood; enough protein and regular meals in the luteal phase, when hunger climbs; and regular exercise for cramps, which a Cochrane review found may cut period pain by a large margin, though on low-quality evidence. The guides under “The cycle” below take each of those in turn, and how many calories you should eat a day explains why the daily total does not change with the phase.
What Changes in the Years Before Menopause
The menopausal transition most often begins between 45 and 55, and its first sign is usually the cycle itself. Periods start to come more often or less often; some women get one every three weeks before they begin to skip, and the irregular stretch runs one to three years before periods stop, with cycles along the way that do not ovulate at all and miss the progesterone rise. That is why a calendar that held for twenty years stops holding, and why symptoms that look unrelated, hot flushes, a racing heart, migraines with a pattern, broken sleep, can sit on the same timeline. The guides under “Perimenopause” below cover the early signs, the symptoms one by one, and what changes about weight, muscle and bone in those years.
When a Cycle Becomes a Pregnancy
Pregnancy is dated from the first day of the last period, not from conception, so the 40 weeks include the two before ovulation. Only about 4 to 5 percent of babies arrive on the due date and about 90 percent within two weeks either side; a first-trimester ultrasound is the most accurate way to date one. Weight gain has a target that depends on where you started: for a pre-pregnancy BMI in the healthy range the Institute of Medicine’s range is 11.3 to 15.9 kg (25 to 35 lb), less for a higher BMI, more for a lower one.
The Guides
Everything in this site’s hormones section, grouped. Each guide is written against primary sources and dated when it changes.
The Cycle
- Foods for the menstrual phase
- Foods for the follicular phase
- Foods for ovulation
- Foods for the luteal phase
- A three-day workout routine for period cramps
- Iron deficiency from heavy periods
- Iron-rich foods for heavy periods: what absorbs
- Seed cycling: what it is and what the science says
- Losing weight on birth control
Estrogen and Progesterone
- Signs of low progesterone
- Foods that support progesterone
- Symptoms of estrogen dominance
- Foods that reduce estrogen dominance
- Signs of low estrogen in your 30s that are not perimenopause
- Foods that help with hormonal bloating
- Daily habits that balance hormones
Cortisol, Thyroid and Insulin
- Signs of high cortisol
- How to lower cortisol: nine daily habits
- Foods that lower cortisol
- Early signs of Hashimoto’s
- A hypothyroidism meal plan
- Early signs of insulin resistance
- Foods for insulin resistance without diabetes
- Losing weight with insulin resistance
- Signs of leptin resistance
- Histamine intolerance symptoms
- Daily habits that reduce brain fog
Perimenopause
- Early signs of perimenopause in your 30s
- Perimenopause symptom relief: what works
- Heart palpitations in perimenopause
- Resting heart rate in perimenopause
- Hormonal migraines in perimenopause
- Low histamine foods for perimenopause
- Recurrent UTIs after menopause
- Lifting heavy in perimenopause: the bone density evidence
- Losing weight in perimenopause
- Not losing weight during perimenopause
- Losing weight after menopause
New guides land in the Hormones and Perimenopause section, which lists every one with its date.
Frequently Asked Questions
What are the four phases of the menstrual cycle?
Menstrual (the period, days 1 to about 5), follicular (day 1 to ovulation, when estrogen rises and an egg matures), ovulation (about day 14 of a 28-day cycle, or 14 days before the next period) and luteal (from ovulation to the day before the next period, when progesterone rises). The follicular phase overlaps the period.
How long is a normal menstrual cycle?
The average is 28 days, and anything from 21 to about 35 days is normal for an adult. A drift of a couple of days from month to month is normal too. The second half of the cycle stays close to two weeks; it is the first half that varies.
When do you ovulate?
About 14 days before the next period starts, whatever the cycle length: around day 14 in a 28-day cycle, day 18 in a 32-day one. The fertile window is the five days before ovulation plus the day itself, because sperm live up to five days and the egg 12 to 24 hours. The ovulation calculator maps the window; a home LH test confirms the day.
Why has my cycle changed in my 40s?
The menopausal transition most often begins between 45 and 55 and shows first in the cycle: periods come more often or less often, sometimes every three weeks before they start to skip, and the irregular stretch lasts one to three years. Very heavy bleeding, bleeding between periods or a pattern of missed periods is worth a doctor’s visit at any age.
Does the phase change how much I should eat?
Not the total. Appetite rises a little in the luteal phase and energy often dips in the menstrual phase, but the daily calorie need is set by size, age, sex and activity, not by the calendar. What helps is iron-rich food around a heavy period and steady protein in the second half of the cycle.
Sources
- The Menstrual Cycle: Menstruation, Ovulation, and How Pregnancy Occurs · American College of Obstetricians and Gynecologists
- Menstrual Cycle (Normal Menstruation): Overview and Phases · Cleveland Clinic
- Pregnancy – identifying fertile days · MedlinePlus (NIH)
- Menstruation | Period · MedlinePlus (NIH)
- Methods for Estimating the Due Date (Committee Opinion No. 700) · American College of Obstetricians and Gynecologists
- Weight Gain During Pregnancy: Reexamining the Guidelines · Institute of Medicine, National Academies
- Menopause · MedlinePlus Medical Encyclopedia (NIH)
- What Is Menopause? · National Institute on Aging (NIH)
- Exercise for dysmenorrhoea · Cochrane Database of Systematic Reviews (PMC)
This page is for general information only and is not a substitute for professional medical advice, diagnosis, or treatment.