Written by the Cycella editorial team · Last reviewed September 28, 2026
Published September 28, 2026

Why is my period late? Common causes besides pregnancy

The short answer

A period that is a few days late is very common and usually not a sign of anything serious. Apart from pregnancy, the most common reasons the NHS lists are stress, sudden weight loss, being overweight, too much exercise, breastfeeding, some hormonal contraception, and conditions like PMOS (the new name for PCOS). If you have missed 3 periods in a row, see a doctor.

How late is “late”?

According to the NHS, most periods come about every 28 days, but anything from every 21 to every 35 days is common. So first, check your own pattern. If your cycles usually run 33 days, a period on day 31 is not late, and one on day 34 is only a day behind.

This is where tracking helps. If you only remember “it came around the start of the month”, a normal 33-day cycle can look late. Counting your cycle in days from the first day of each period gives you a real answer. (If you use the Nepali calendar, see how to track your period with BS dates.)

Common reasons a period is late

Pregnancy

If there is any chance you could be pregnant, a home pregnancy test is the quickest way to rule it in or out. If the test is negative and your period still hasn’t come, it’s reasonable to test again a few days later. A doctor or health post can also help.

Stress

Stress is one of the most common causes the NHS lists. Exams, a move, family pressure, illness or a big life change can all delay ovulation. When ovulation is late, the period is late too, because a period usually comes about 14 days after ovulation.

Sudden weight loss, or being overweight

Both are on the NHS list. Losing a lot of weight quickly, or eating too little, can stop periods. Carrying extra weight can also make cycles less regular.

Too much exercise

Very intense training, especially combined with eating too little, can delay or stop periods.

PMOS (formerly called PCOS)

Polyendocrine metabolic ovarian syndrome, still widely known as PCOS or PCOD, is a common hormonal condition. The WHO estimates it affects 10 to 13% of women worldwide, and up to 70% of them are undiagnosed. Irregular or missing periods are one of its main signs, often together with acne, extra facial or body hair, or weight gain. Read PCOS, PCOD and PMOS: what’s the difference?

Thyroid problems and other health conditions

The NHS notes that periods can also stop because of medical conditions such as thyroid disorders, diabetes or heart disease. A doctor can check with a simple blood test.

Breastfeeding and hormonal contraception

Periods often don’t return straight away while breastfeeding. Some hormonal contraceptive methods also make periods lighter, irregular or stop them. If you have questions about a method you use, ask the health worker who gave it to you.

Perimenopause

For women usually between 45 and 55, irregular or missed periods can be the start of menopause.

When to see a doctor

The NHS advises seeing a doctor if:

• you’ve missed your period 3 times in a row
• your periods have not started by the time you’re 15
• your periods have become irregular
• you have missed periods along with other symptoms, such as weight changes, feeling very tired, extra facial hair, or skin changes

Go sooner if you have severe pain, very heavy bleeding, or feel unwell.

What to note before your appointment

Bring the dates your last few periods started, how long each lasted, and anything that changed (stress, weight, new medicine, illness). A doctor can say much more from real dates than from “it’s been irregular”. Cycella keeps this history for you and can turn it into a one-page doctor report.