Why are my periods irregular?

Cycles that shift by a few days from month to month are common, and irregular periods are usually explained by something ordinary. A cycle of about 21 to 35 days is considered typical, and ACOG cites research putting truly irregular cycles at somewhere between 14% and 25% of women. The Saudi Ministry of Health describes a cycle that averages 28 days but can vary between 20 and 40. What matters is less any single late or early month than a pattern you can see over several cycles.

The NHS lists these among the common reasons periods become irregular or stop:

• Stress. Ongoing stress is one of the causes the NHS names for a missed or unpredictable period.
• Weight change or heavy exercise. Sudden weight loss, being overweight, and exercising very intensely can each disrupt your cycle.
• PCOS (now also called PMOS). Irregular periods or long gaps between them are one of the main symptoms the NHS lists, often alongside extra hair growth on the face or body and difficulty losing weight.
• Thyroid problems and diabetes. The NHS notes that periods can stop or change because of these conditions.
• Hormonal contraception. Some methods change or pause bleeding, especially in the first months of starting or stopping them. If you are on pills to delay your period, spotting and shifted timing are part of that picture.
• Breastfeeding. Periods may be absent or unpredictable while you feed. See when your period usually returns after giving birth.
• Perimenopause. For many women the first sign is a change in the periods: the NHS says they may come more or less often, and bleeding may get heavier or lighter. The NHS places the start of menopause usually between 45 and 55.
• Being early in your cycles. The Saudi Ministry of Health notes that irregularity is common in adolescence, because the body takes 2 to 3 years after the first period to settle into a rhythm.

Pregnancy is also on the NHS list, so if there is any chance you are pregnant, a home test is a sensible first step.

It is worth talking to a doctor if you have missed 3 periods in a row, if your periods have not started by 15, if your periods have become irregular when they used to be steady, or if a missed period comes with weight change, tiredness, or hair growth on your face. The Saudi Ministry of Health also lists periods lasting over 8 days, very heavy bleeding, and bleeding outside your period or after menopause. A doctor can look at your history and arrange tests; this page cannot tell you which cause, if any, applies to you, and none of the above is a reason to self-diagnose.

For a woman who prays and fasts, unpredictable bleeding raises a second question: is it hayd or not? Irregular timing does not on its own settle that. How istihadah differs from hayd explains the signs scholars use, and what counts as hayd gives the baseline. If your period is not late but simply longer or shorter than you expected, how long a cycle should be covers the range, and why a period can be late covers the delayed case in more depth.

Irregular cycles are much easier to talk about with a doctor when you have dates rather than memory. Logging when bleeding starts and ends, month after month, shows whether the pattern is drifting or just varying; see what to look for in a period tracker built for Muslim women. Nisaa is free on the App Store and does this, so you bring your own record to the appointment.

If you are bleeding twice in one calendar month, why you might get your period twice in a month explains the usual reasons.