Last updated: March 2026
Understanding Your Menstrual Cycle
The menstrual cycle is a monthly process that prepares the body for pregnancy. A typical cycle ranges from 21 to 35 days, measured from the first day of one period to the first day of the next. The average is 28 days, but many healthy cycles fall outside this number.
Your cycle has four main phases. Menstruation (days 1-5) is when the uterine lining sheds, producing your period. The follicular phase (days 1-13) overlaps with menstruation — follicles in the ovary mature under the influence of FSH hormone.
Ovulation (around day 14) occurs when a surge in LH hormone triggers the release of a mature egg. The luteal phase (days 15-28) follows — the empty follicle produces progesterone to maintain the uterine lining. If the egg isn't fertilized, progesterone drops and the cycle starts again.
Tracking your period helps you recognize patterns and detect changes early. Sudden shifts in cycle length, flow, or symptoms can signal hormonal changes, stress effects, or health conditions. Many gynecologists ask about your cycle patterns during checkups.
Common reasons for irregular periods include stress, significant weight changes, excessive exercise, thyroid disorders, and polycystic ovary syndrome (PCOS). If your cycles are consistently outside the 21-35 day range, or if you skip periods entirely, it's worth consulting your healthcare provider.
Frequently Asked Questions
When will my next period start?
Your next period is predicted by adding your average cycle length to the first day of your last period. For example, if your last period started March 1 and your cycle is 28 days, your next period should start around March 29. This calculator projects 3 cycles forward.
Why is my period late?
Periods can be late due to stress, travel, illness, weight changes, excessive exercise, or hormonal fluctuations. An occasional late period is normal. If your period is consistently irregular or more than 7 days late, consider taking a pregnancy test or consulting your healthcare provider.
What's a normal period length?
Most periods last 2-7 days, with an average of about 5 days. Bleeding is typically heaviest during the first 2 days and gradually lightens. Periods consistently shorter than 2 days or longer than 7 days are worth discussing with your doctor.
How do I track my cycle accurately?
Start counting from the first day of full bleeding (not spotting). Day 1 is the first day of your period. Count each day until the day before your next period starts — that total is your cycle length. Track at least 3 cycles to determine your average.
Is an irregular cycle something to worry about?
Some cycle variation (1-5 days) is perfectly normal. However, cycles consistently shorter than 21 days or longer than 35 days, skipping periods, or sudden changes in your pattern may indicate conditions like PCOS, thyroid issues, or other hormonal imbalances worth investigating.