How your cycle is mapped
The four phases of the menstrual cycle scale proportionally with your cycle length. The luteal phase (from ovulation to your next period) stays close to 14 days regardless of cycle length - it is the follicular phase that stretches or shrinks to account for shorter or longer cycles.
Phase boundaries are calculated as fractions of your total cycle length, so a 35-day cycle has a longer follicular phase than a 21-day cycle, while the luteal phase remains roughly constant. The phase you are in today is based on how many days have passed since your last period.
Cycle phases at a glance
Menstrual: days 1-5 on average. Uterine lining sheds. Estrogen and progesterone are low.
Follicular: overlaps with menstruation and continues until ovulation. Estrogen rises as a follicle matures.
Ovulation: a brief window - usually 1-3 days - around day 14 (in a 28-day cycle). The egg is released.
Luteal: roughly days 15-28. Progesterone rises to prepare the uterus. If no fertilization occurs, levels fall and the next period begins.
To find out when you are most likely to ovulate, use the ovulation calculator. For a simple list of upcoming period dates, the period calculator is the quickest tool.
Frequently asked questions
What are the four phases of the menstrual cycle?
The menstrual phase is your period. The follicular phase follows as an egg matures and estrogen rises. Ovulation is the release of the egg, around the middle of the cycle. The luteal phase is the roughly 14 days after ovulation, ending with your next period if you don't conceive.
How long is a normal menstrual cycle?
A typical cycle is 21 to 35 days, counted from the first day of one period to the first day of the next. Cycles can vary a few days month to month, which is normal. Consistently very short, very long, or unpredictable cycles are worth discussing with a doctor.
How is this different from the period calculator?
The period calculator focuses on one thing: when your next period is due. This menstrual cycle calculator maps your whole cycle - which phase you're in today, how the four phases break down, and several upcoming periods at once.
These calculators give estimates based on cycle averages and standard formulas. They are for general information only and are not medical advice. For anything concerning your health or pregnancy, talk to a qualified healthcare provider.