Cycle Length Calculator
Enter the start dates of your last 3-6 periods to calculate your average cycle length and see how regular your cycles are.
Understanding Your Cycle Length
What Determines Your Cycle Length?
Your menstrual cycle length is primarily determined by two phases: the follicular phase (from the first day of your period to ovulation) and the luteal phase (from ovulation to your next period). While the luteal phase tends to be fairly consistent at 12-14 days, the follicular phase is more variable and accounts for most of the differences in cycle length between women. Hormones like estrogen, progesterone, FSH, and LH work together to regulate these phases. Genetics, age, body weight, stress levels, and overall health all influence how these hormones function, which in turn affects your cycle length.
Understanding Irregular Cycles
Cycle variation of up to 3 days is considered regular and completely normal. Variation of 4-7 days is somewhat irregular but usually not a concern, especially during puberty, postpartum, or perimenopause. Cycles that vary by more than 7 days are considered irregular. Common causes include polycystic ovary syndrome (PCOS), thyroid disorders, significant stress, extreme exercise, eating disorders, and certain medications. Occasional irregularity can also result from illness, travel, or temporary lifestyle changes. It is worth noting that your cycle length can naturally change over the years. Many women experience shorter cycles as they age, with cycle length gradually decreasing through their 30s and 40s.
When to See a Doctor About Cycle Length
While some variation in cycle length is normal, you should consult a healthcare provider if: • Your cycles are consistently shorter than 21 days or longer than 35 days • Your cycle length suddenly changes significantly (by more than a week) • You experience very heavy bleeding or periods lasting more than 7 days • You go more than 90 days without a period (and are not pregnant) • You have painful symptoms that interfere with daily life Bringing a record of your cycle history to your appointment can help your provider identify patterns. Cyla's Health Report feature generates detailed summaries that are easy to share with your doctor.
Frequently Asked Questions
Automatic Cycle Analysis
Cyla tracks your cycles automatically and uses AI to detect patterns, predict irregularities, and give you insights. Free to download.
