How this works
We add your usual cycle length to the first day of your last period to find when your next one was expected, then count from there. Up to three days either side counts as on time, because that much shift between cycles is normal for many people.
A normal cycle is usually 21 to 35 days, counted from the first day of one period to the first day of the next. Published clinical guidance treats a difference of up to 7 to 9 days between your shortest and longest cycles as regular, so one cycle running a week long doesn’t automatically mean there’s a problem.
Then the tool shows the causes that fit your answers. It doesn’t rank them by probability, as that would claim a certainty nobody has. Read how every calculation works.
Why is my period late? What this checker looks for
The causes below are the ones listed in NHS guidance on missed periods. The checker shows those that fit your answers, along with what usually helps next.
| Possible cause | What to know | Usual next step |
|---|---|---|
| Pregnancy | The first cause to rule out if there’s any chance of it | Take a home test |
| Stress | A common cause of late periods | A GP can offer advice or therapy to reduce stress |
| Weight changes | Sudden weight loss and being overweight can both have an effect | A GP can advise on maintaining a healthy weight |
| Too much exercise | Can delay or stop periods | Mention your training to a GP if periods stop |
| Hormonal contraception | The pill, injection and IUS can all change your bleeding | Ask whoever prescribed it what to expect |
| PCOS, now also called PMOS | A hormonal condition that can cause irregular periods | Blood tests, and treatment that may include the combined pill |
| Thyroid and other conditions | Thyroid problems, diabetes and heart disease can stop periods | A GP can arrange blood tests |
| Perimenopause | Usually between the ages of 45 and 55 | A GP can discuss options, including HRT |
A worked example
Say your last period started on 1 March and your cycle is usually 30 days. Your next period would be expected on 31 March. On 2 April you’d be 2 days past your estimate, which still counts as on time. On 5 April you’d be 5 days late, and the checker would suggest a pregnancy test if pregnancy is possible.
This is why your own cycle length matters. Compared with a 28-day average, that same period would look a week late on 5 April, even though it’s only 5 days past your own estimate.
What to do when your period is late
- Check for urgent symptoms. If you could be pregnant and have sudden, intense tummy pain, or feel very dizzy or faint, call emergency services.
- Take a pregnancy test if there’s any chance. Tests are most reliable from the first day of a missed period. If you don’t know when it was due, test at least 21 days after you last had unprotected sex.
- Test again if needed. A positive result is almost certainly correct, but a negative one is less reliable. Wait a few days and try again, and speak to a GP if the second test is also negative and your period still hasn’t come.
- Look at what’s changed. Stress, weight, training and contraception are all worth considering, especially if the timing lines up.
- Log it. The period tracker builds a record of your dates, which helps if you do see a doctor.
A GP will usually ask about your health and may arrange blood tests. They can refer you to a gynaecologist or endocrinologist if you need further tests or scans. Treatment depends on the cause.