Why is my period late?

A late period can cause anxiety and confusion, especially if your cycle has been regular for some time. While a delay may simply reflect normal variation, it can also signal changes in health, lifestyle or hormonal balance. Understanding why your period is late empowers you to respond calmly, whether that means waiting a few days, taking a pregnancy test or consulting your GP. This article explains how the menstrual cycle works, what common factors delay menstruation, when a late period is nothing to worry about and when to seek professional advice.

How the menstrual cycle works
Each month a delicate interplay of hormones prepares the body for potential pregnancy. Follicle stimulating hormone prompts ovarian follicles to mature one egg. Rising oestrogen levels thicken the uterine lining. Mid‑cycle a surge of luteinising hormone triggers ovulation, releasing an egg. After ovulation progesterone dominates, maintaining the uterine lining. If fertilisation does not occur, both oestrogen and progesterone levels fall, causing the lining to shed as menstruation. The typical menstrual cycle lasts 21 to 35 days, with bleeding lasting two to seven days. Minor fluctuations of a few days each month are common and usually harmless.

Pregnancy as the most common cause
For women who are sexually active without reliable contraception, the first consideration for a late period is pregnancy. Once an egg is fertilised and implants in the uterine lining, it secretes human chorionic gonadotrophin which prevents the hormonal drop that triggers bleeding. A home pregnancy test taken after a missed period offers a quick way to confirm or exclude this possibility. If the test is positive you can contact your GP or midwife to begin prenatal care.

Stress and emotional factors
Stressful life events such as work pressure, relationship difficulties or major life changes can disrupt the delicate hormonal balance underpinning your cycle. The body’s stress response releases cortisol and adrenaline which can suppress the hormones that regulate ovulation. As a result your period may come early, late or not at all in that cycle. If stress contributes to a missed period, finding ways to manage pressure through relaxation techniques, physical activity and talking therapies often helps restore regularity.

Changes in weight and body composition
Significant weight gain or loss can disturb menstrual patterns. Low body weight and very low body fat reduce the production of oestrogen, which is essential for ovulation. This often occurs in women with disordered eating, intense exercise routines or certain medical conditions. Conversely rapid weight gain can elevate insulin levels and create a state of hormonal imbalance. Both extremes can lead to missed or irregular periods. Gradual, sustainable dietary and exercise changes under professional guidance support healthy hormone levels and menstrual function.

Excessive exercise
While regular moderate exercise tends to regulate cycles, intense training regimes common among athletes or fitness enthusiasts may cause the body to enter an energy conservation mode. When calorie intake fails to match the energy burned, the brain signals the ovaries to reduce reproductive activity. As a result ovulation may skip a month and menstruation may not occur. Reducing intensity, ensuring adequate nutrition and balancing rest days are key to resuming normal cycles.

Breastfeeding and early motherhood
Prolactin, the hormone responsible for milk production, also inhibits the reproductive hormones that trigger ovulation. Many women find that their periods do not return until they reduce breastfeeding frequency or wean completely. The timing varies widely; some resume regular cycles a few months after birth, while others do not menstruate for a year or longer. If you wish to conceive again, discussing appropriate contraception and weaning strategies with your GP can help you plan effectively.

Hormonal contraceptives and medications
Starting, stopping or changing hormonal contraception such as the combined pill, progestogen-only pill, patch or implant can lead to irregular bleeding patterns. After discontinuing the pill your cycle may take a few months to regulate. Some medications including certain antidepressants, antipsychotics, chemotherapy drugs and high‑dose corticosteroids can also interfere with your menstrual cycle. If you suspect a medicine affects your period, consult your prescriber before making any changes.

Perimenopause and the approach of menopause
For women in their forties or early fifties irregular cycles become increasingly common as ovarian reserve declines. This perimenopausal phase can include cycles that shorten, lengthen or skip altogether, often accompanied by other symptoms such as hot flushes, mood changes or sleep disturbances. Once you have gone twelve consecutive months without a period, you reach menopause. If you experience significant discomfort or very heavy, prolonged bleeding during perimenopause, GP assessment may identify hormone replacement therapy or other treatments to improve quality of life.

Polycystic ovary syndrome and other endocrine disorders
Polycystic ovary syndrome is a common hormonal condition that often leads to irregular or absent periods. In PCOS you may experience high levels of androgens, multiple small ovarian follicles and insulin resistance. Weight management, dietary changes and medications such as metformin or hormonal contraception can help regulate cycles. Less common endocrine disorders such as thyroid dysfunction, hyperprolactinaemia or adrenal gland abnormalities can also delay menstruation. Blood tests to evaluate thyroid, prolactin and adrenal hormone levels can identify underlying conditions requiring specific treatment.

Underlying medical conditions
Chronic diseases such as diabetes, coeliac disease and inflammatory bowel disease can affect menstrual regularity through nutrient malabsorption, systemic inflammation and stress responses. Autoimmune disorders and severe infections place additional strain on the body’s resources, leading to occasional cycle disruptions. Maintaining good control of chronic conditions with medication, dietary management and regular medical reviews supports overall health and menstrual stability.

When to seek medical advice
If your period is more than a week late and pregnancy is ruled out, or if you experience very heavy bleeding, severe pain or symptoms such as fainting or severe headaches, you should contact your GP. Likewise, if your cycle skips more than three consecutive months outside of pregnancy, breastfeeding or perimenopause, a medical evaluation is necessary. Your GP will take a full history, perform a physical examination and may request blood tests or an ultrasound scan to determine the cause of your delayed period and guide appropriate treatment.

Self‑care and monitoring
Keeping a menstrual diary or using a cycle‑tracking app helps you identify patterns and potential triggers for changes in your period. Recording factors such as stress levels, exercise intensity, dietary changes and medication use provides valuable information for you and your GP. Ensuring a balanced diet rich in whole grains, lean proteins, healthy fats, ample water and moderated caffeine and alcohol intake supports hormonal balance. Regular moderate exercise, good sleep hygiene and stress management techniques such as mindfulness or gentle yoga help maintain a healthy cycle.

Emotional impact and support
A late period often sparks worry about fertility, weight, ageing or health issues. Sharing concerns with a trusted partner, friend or healthcare provider can offer reassurance and practical advice. If anxiety about your cycle becomes overwhelming, speaking to a counsellor or joining a support group can help you cope with uncertainties and reduce stress, which in turn promotes hormonal harmony.

Summary
A late period may simply reflect natural variation in your cycle or result from factors such as pregnancy, stress, changes in weight or hormonal contraception. Less commonly it may signal underlying conditions like PCOS, thyroid dysfunction or chronic illness. Maintaining a healthy lifestyle, tracking your cycle and knowing when to consult your GP will help you manage temporary delays and address persistent irregularities. Understanding the reasons behind a late period empowers you to take control of your menstrual health and seek timely care when needed.