Menstrual Cycle Basics: Phases, Symptoms, & Timing

4 hours ago
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Author: Lauren Calicchia, MD Student, University of Toronto

Introduction

The menstrual cycle is a monthly process that prepares the body for pregnancy. Instead of being the same every day, this cycle has stages that are due to changes in hormones [1]. These changes impact not just the uterus, but energy, mood, and many other things throughout the month.

Important note:

These day ranges are based on a 28-day cycle. Many people have shorter or longer cycles, and that is completely normal.

Figure 1. An overview of the menstrual cycle phases — **Figure 1.** An overview of the menstrual cycle phases

1. Menstrual Phase: Day 1-5

The menstrual phase begins on the first day of bleeding. At this point, estrogen and progesterone levels are low, which tells the uterus to shed the lining that built up during the previous cycle. This shedding is what causes a period [1].

Because hormone levels are at their lowest, some people notice changes to their body and mood during this phase, including:

Cramping
Feeling tired or having low energy
Headaches or body aches [2]

These symptoms occur because estrogen normally helps regulate pain and energy. When estrogen drops, the body becomes more sensitive to discomfort and tiredness [2].

2. Follicular Phase: Day 1-14

The follicular phase happens at the same time as the menstrual phase and continues until ovulation. Estrogen levels slowly rise, and the lining of the uterus starts to rebuild [3].

As estrogen increases, many people feel changes such as:

Feeling more focused [4]
Having more energy
Feeling happier [5]

This happens because estrogen helps the brain make a hormone called serotonin (the hormone that makes you happy) and also increases blood flow to the brain, which can make you feel more concentrated and happier [5].

3. Ovulation: Day 14

Ovulation happens when a rise in a hormone called luteinizing hormone (LH) causes the ovary to release an egg. This typically happens around the middle of the cycle, but the exact timing varies from person to person [1].

Around ovulation, estrogen levels peak, which can lead to:

Increased confidence or sociability
Higher libido (sex drive)
Clear, stretchy vaginal discharge
One-sided pelvic discomfort [6]

Ovulation is the most fertile window of the cycle. The egg survives for about 24 hours, while sperm can live in the body for up to five days [6].

4. Luteal Phase: Day 15-28

The luteal phase starts after ovulation and continues until your next period starts. In this phase, your body makes more of a hormone called progesterone, which helps prepare the uterus in case a pregnancy happens. If a pregnancy does not happen in this cycle, both progesterone and estrogen levels start to fall [1].

Progesterone’s effects can include:

Feeling bloating
Breast soreness
Constipation
Mood changes, like feeling more emotional or irritable [7]

As hormone levels drop at the end of this phase, some people experience premenstrual symptoms (PMS) [7]. These symptoms are a response to changes in hormones. They are not a sign of personal weakness or stress, they are just how the body’s hormones work.

Figure 2. An overview of the phases of the menstrual cycle and the hormonal changes with each stage. — **Figure 2.** An overview of the phases of the menstrual cycle and the hormonal changes with each stage.

Why Do Symptoms Change Throughout the Cycle?

Hormones play an important role in the body, not just the reproductive system. They affect the brain, gut, muscles, and immune system. As hormones like estrogen and progesterone naturally rise and fall, they can influence things like:

Energy levels
Mood and emotions
How sensitive you are to pain
Appetite and food cravings
And many other day-to-day changes

Learning how these hormone patterns affect your body can help you better understand what feels normal for you and make sense of changes you may notice throughout your cycle.

What's Normal vs. Not Normal

Normal

Cycle length between 21-35 days
Periods lasting 3-7 days
Mild cramps or mood changes [8]

Not Normal

Bleeding for more than 8 days
Severe pain affecting daily life
Periods less than 21 days or more than 34 days apart [8]
Bleeding between periods or after sex

When to Seek Medical Advice

Some changes in cycle length and symptoms are normal. However, it’s important to speak with a healthcare provider if you experience:

Severe pain that interferes with daily life
Very heavy or prolonged bleeding
Highly irregular cycles
Severe mood symptoms before periods [9]

Sources:

Thiyagarajan DK. Physiology, menstrual cycle [Internet]. U.S. National Library of Medicine; 2024 [cited 2026 Jan 10]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK500020/
Raves DM, Herrera WD, Darnell ME, Rice T, Friedman C, Moratti SC, et al. A survey assessing the impact of symptoms related to the menstrual cycle and perceptions of workplace productivity: Considerations for employer-sponsored menstrual health programs. BMC Women’s Health. 2025 Aug 30;25(1). doi:10.1186/s12905-025-03833-w
Reed BG. The normal menstrual cycle and the control of ovulation [Internet]. U.S. National Library of Medicine; 2018 [cited 2026 Jan 10]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK279054/
Sawicka AK, Michalak KM, Naparło B, Bermudo-Gallaguet A, Mataró M, Winklewski PJ, et al. Menstrual cycle phase influences cognitive performance in women and modulates sex differences: A combined longitudinal and cross-sectional study. Biology. 2025 Aug 15;14(8):1060. doi:10.3390/biology14081060
Kale MB, Wankhede NL, Goyanka BK, Gupta R, Bishoyi AK, Nathiya D, et al. Unveiling the Neurotransmitter Symphony: Dynamic shifts in neurotransmitter levels during menstruation. Reproductive Sciences. 2024 Nov 19;32(1):26–40. doi:10.1007/s43032-024-01740-3
Cappelletti M, Wallen K. Increasing women’s sexual desire: The comparative effectiveness of estrogens and androgens. Hormones and Behavior. 2016 Feb;78:178–93. doi:10.1016/j.yhbeh.2015.11.003
Gudipally PR. Premenstrual syndrome [Internet]. U.S. National Library of Medicine; 2023 [cited 2026 Jan 10]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK560698/
Menstruation in girls and adolescents: Using the menstrual cycle as a vital sign [Internet]. [cited 2026 Jan 10]. Available from: https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2015/12/menstruation-in-girls-and-adolescents-using-the-menstrual-cycle-as-a-vital-sign
Mikes BA. Abnormal uterine bleeding [Internet]. U.S. National Library of Medicine; 2025 [cited 2026 Jan 10]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532913/

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