Medically Reviewed By
MBBS (Col), MD (Col) · SLMC No. 27329
Consultant Physician · Sineth Hospitals, Boralasgamuwa
Enter the first day of bleeding of your last few periods. This tool estimates your average cycle length, checks whether your cycles appear regular, and predicts your next period and fertile window.
Enter the first day of bleeding of your last few periods. This tool estimates your average cycle length, checks whether your cycles appear regular, and predicts your next period and fertile window.
These dates are estimates only.
Enter the first day of actual bleeding for each of your recent periods. You need at least 3 dates; entering up to 6 gives a more reliable estimate. Add dates in any order — the tool sorts them automatically. Click Calculate to see your average cycle length, cycle regularity classification, and estimated next period and fertile window.
Cycle length is the number of days from the first day of one period to the first day of the next period. For example, if one period started on the 1st and the next started on the 29th, the cycle length is 28 days. Most cycles range from about 21 to 35 days, though shorter or longer cycles can be normal for some people.
This tool measures the difference between your shortest and longest observed cycle. A variation of 7 days or less is classified as regular. A variation of 8 to 14 days is classified as mildly variable. A variation of more than 14 days is classified as irregular. This is based on the dates you entered and is an estimate — it does not replace clinical assessment.
Cycle irregularity is common and can be normal, particularly during teenage years, perimenopause, or after stopping hormonal contraception. It can also be associated with polycystic ovary syndrome (PCOS), thyroid conditions, significant weight changes, high levels of stress, or excessive exercise. If you are concerned about persistent cycle irregularity, a medical assessment is recommended.
The fertile window estimate assumes ovulation occurs about 14 days before the next expected period. For regular cycles, this estimate is reasonably reliable. For mildly variable or irregular cycles, the estimate becomes less accurate. If accurate ovulation tracking is important to you, methods such as basal body temperature recording, cervical mucus monitoring, or ovulation predictor kits may provide additional information.