When will my period come, and what is a normal cycle?
Cycle length is counted from the first day of one period to the first day of the next. For adults, the usual range is 21 to 35 days, and the period itself lasts 2 to 7 days. The average is around 28 days, though few people have exactly the same length every month.
A difference of a few days from one month to the next is common and is not, on its own, a reason to worry. The calculator above uses the average of your recent cycles, so the result is an estimate rather than an exact prediction – especially if your cycle is irregular.
Late period: common causes
A period that arrives a few days later or earlier than expected is often still within the usual range. A period is generally considered late once it has not arrived about seven days after the expected date. For anyone who is sexually active, pregnancy is the most common cause, so a pregnancy test is the first step.
Other common circumstances include stress, a large change in body weight, intense exercise, illness or infection, thyroid problems, polycystic ovary syndrome (PCOS), and perimenopause. Hormonal contraception (the pill, an IUD, an injection) can also change or temporarily stop bleeding.
When to see a doctor or gynaecologist
It is worth seeing a doctor or gynaecologist if your period has not arrived for three months or more and you are not pregnant, if your cycle is very irregular from month to month, or if bleeding is unusually heavy or painful.
This calculator is an informational tool, not a method of contraception, and it does not replace a check-up. If you are planning a pregnancy, tracking fertility, or want closer monitoring of your cycle, talking to a gynaecologist is the next step.
Frequently asked questions
When will I get my period?
The calculator predicts a date from the first day of your last period and your average cycle length. The estimate is more reliable with a regular cycle than with an irregular one, where it is more of a rough direction.
How many days can a period be late and still be normal?
For adults, a difference of up to about seven days from the expected date is still within the usual range. A longer or repeated delay is a reason to pay more attention to the cause.
Why is my period late if I am not pregnant?
Common causes without pregnancy include stress, a significant change in body weight, intense exercise, illness, thyroid problems, polycystic ovary syndrome (PCOS), or perimenopause. Hormonal contraception can also change bleeding.
What is a normal cycle length?
For adults, the usual cycle range is 21 to 35 days, and the period itself lasts 2 to 7 days. The average cycle length is around 28 days.
When is a late period a reason to see a doctor?
It is worth seeing a doctor or gynaecologist if your period has not arrived for three months or more, if your cycle is very irregular, or if bleeding is unusually heavy or painful.
Sources
Updated: October 2026
For information only, not a substitute for medical advice.