Menstrual Cycle and Ovulation Calculator
Estimate your next period and a possible ovulation window using your usual regular cycle length. The dates are only estimates: your body does not necessarily follow an exact calendar.
Calculate Your Estimated Dates
Your Estimated Dates
Estimated Fertile Window:
Why Might Your Period Be Late?
A single late period does not necessarily mean something is wrong. Several common factors can affect when menstrual bleeding begins. Your overall circumstances are more informative than any one date.
Stress and Changes in Routine
Stress or changes in sleep patterns and daily routine can sometimes affect the menstrual cycle.
Weight Changes or Intense Exercise
Substantial weight loss or gain, or very intensive exercise, can affect ovulation.
Possible Pregnancy
If you have had sex and your period is late, a pregnancy test can help check this possibility.
Contraception and Breastfeeding
Some hormonal contraceptives, stopping or changing methods, and breastfeeding can alter bleeding patterns.
Age and Hormonal Changes
Cycles may vary during adolescence and in the years leading up to menopause.
Causes That May Require Medical Assessment
Thyroid disorders or polycystic ovary syndrome (PCOS) can cause irregular cycles; a medical assessment can help investigate them.
When Should You See a Gynecologist?
Medical advice is helpful if your cycles become irregular, if you miss three consecutive periods, if bleeding lasts unusually long, or if you experience unusual pain, bleeding between periods or difficulties conceiving. You do not need to wait three months if your symptoms concern you.
If pregnancy is possible and you develop severe abdominal pain, faintness or heavy bleeding, seek urgent medical assessment.
During the consultation, the gynecologist will consider your dates, medical history, treatments and symptoms. Depending on the situation, she may discuss pregnancy testing, blood tests or an ultrasound, without requesting unnecessary investigations.
Book an Appointment at the PracticeMenstrual Cycle: Frequently Asked Questions
Does a Normal Cycle Have to Be 28 Days Long?
No. In adults, a cycle lasting 21 to 35 days can be normal if its length remains relatively consistent.
Can I Know My Exact Ovulation Date?
No. A calendar calculation only indicates a possible time. Ovulation may occur earlier or later, even in regular cycles.
Why Is My Period a Few Days Late?
Stress, weight changes, hormonal treatments and pregnancy are among the possibilities. An isolated delay is not necessarily a cause for alarm.
What Should I Do if My Cycles Are Irregular?
Do not rely on the calculator alone. An in-person consultation can help you understand your symptoms and discuss any appropriate investigations.
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Medical information: NHS guidance on irregular and missed periods; ACOG guidance on missed periods. This informational tool does not collect or store the dates you enter. NHS · ACOG