Late Period Calculator — Find Out If Your Period Is Late and Why

Why is my period late? The most common reasons

A late period — defined as a period that hasn't arrived within 5–7 days of its expected date — is one of the most common menstrual concerns. And the vast majority of the time, the reason is not pregnancy. Understanding the wide range of factors that can delay a period can take a lot of the anxiety out of waiting.

Your menstrual cycle is regulated by a precise hormonal chain of events that starts in your brain, not your uterus. Any disruption to the signals at the top of that chain can delay ovulation, and because your period follows ovulation by roughly 14 days, a delayed ovulation means a delayed period. Here are the most common culprits:

• Stress — physical or emotional stress raises cortisol, which can suppress the hormonal signals that trigger ovulation
• Significant weight changes — rapid weight gain or loss disrupts oestrogen levels, affecting the cycle
• Illness — even a short-term illness like flu can delay ovulation and push your period back
• Travel and time zone changes — disrupts circadian rhythms, which influence hormonal timing
• Hormonal contraception changes — starting, stopping, or switching hormonal birth control can cause cycles to shift for several months
• PCOS — polycystic ovary syndrome causes irregular or infrequent ovulation, leading to variable cycle lengths
• Thyroid disorders — both overactive and underactive thyroid can affect menstrual regularity
• Perimenopause — from your early 40s, hormonal changes can cause cycles to become unpredictable

How stress delays your period — the science

The connection between stress and late periods isn't just anecdotal — it's well-documented biology. Your hypothalamus, the brain region that orchestrates your menstrual cycle, is acutely sensitive to stress signals. Here's what happens:

When you're under stress, your adrenal glands release cortisol. Elevated cortisol suppresses the hypothalamus's release of gonadotropin-releasing hormone (GnRH). GnRH is the trigger for your pituitary gland to release luteinising hormone (LH) and follicle-stimulating hormone (FSH). Without adequate LH and FSH, ovulation is delayed or skipped entirely. No ovulation means no progesterone rise, which means the uterine lining doesn't get the signal to shed — and your period doesn't come.

What's important to understand is that this isn't a malfunction. It's your body making a sensible physiological decision: if your brain perceives threat or deprivation, it pauses the reproductive system. This is a protective mechanism, not a broken one.

The good news is that once the stressor resolves, the cycle usually resumes. You may ovulate a little later than usual and your period will follow. Tracking your cycle over several months using our period calculator gives you the data to spot these patterns in your own body.

When is a period actually considered "late"?

Cycle length naturally varies by a few days from month to month, even in people with regular cycles. A difference of 1–4 days between cycles is completely normal. So your period isn't truly "late" if it arrives 2–3 days after your expected date — that's just normal variation.

A period is generally considered late when it's 5 or more days past its expected date. At 7 or more days, it's worth paying closer attention. At this point, if you've had unprotected sex, a pregnancy test is the logical next step. If pregnancy isn't a possibility, thinking about what has changed in your life recently — stress levels, sleep, diet, illness, travel, medication — is often productive.

Missing a period entirely for one cycle (amenorrhoea for one cycle) is common and usually resolves without intervention. Missing three or more consecutive periods is a clinical threshold that warrants medical evaluation — both to rule out pregnancy and to investigate hormonal, thyroid, or other underlying causes.

Should you take a pregnancy test?

If you've had unprotected sex in the weeks before your missed period, a pregnancy test is a straightforward and reassuring thing to do. Modern home pregnancy tests are highly accurate from the first day of your missed period — they detect the pregnancy hormone hCG (human chorionic gonadotropin), which the body begins producing after a fertilised egg implants in the uterus.

For the most reliable result: take the test first thing in the morning, when urine is most concentrated and hCG levels are highest. If you get a negative result but your period still doesn't arrive in the next 2–3 days, test again — early testing can occasionally give false negatives if hCG hasn't reached detectable levels yet. A faint line is still a positive result.

A negative test with a late period is actually the most common scenario — it usually means ovulation was simply delayed this cycle, which then pushed the period back. Give your body a little more time, and it will usually catch up.

When should you see a doctor about a late period?

Most late periods resolve on their own without any medical intervention. But there are specific circumstances where speaking to a doctor is the right call:

• Your period is more than 7 days late and there's no obvious lifestyle explanation
• You've missed three or more consecutive periods (and you're not pregnant)
• You have other symptoms alongside the late period — unusual discharge, pelvic pain, unexplained weight changes, excessive hair growth, or significant acne
• A home pregnancy test is positive
• Your cycles have changed significantly from your usual pattern without explanation
• You're under 40 and your cycles have become very irregular (potentially indicating early perimenopause or a hormonal condition)

A GP can run simple hormone blood tests to check thyroid function, reproductive hormones (FSH, LH, prolactin, oestradiol), and other relevant markers. Many of the most common causes of late periods — thyroid issues, PCOS, hormonal imbalances — are easily identified with a blood test and have effective treatments. You deserve to understand what's happening in your body.