This is general information, not medical advice.
A cycle is counted from the first day of one period to the day before the next. The commonly used four-phase description is:
1. Menstrual phase
Bleeding begins as the uterine lining sheds. Day 1 of bleeding is day 1 of the cycle. Many people notice cramps, tiredness or lower energy.
2. Follicular phase
Starts on day 1 too and runs until ovulation. The body prepares an egg to be released, and the uterine lining rebuilds. Energy often rises as the period ends.
3. Ovulation
An egg is released from an ovary. It is typically roughly two weeks before the next period, but timing varies.
4. Luteal phase
After ovulation, the body prepares for a possible pregnancy. If there is none, hormone levels fall and a period follows. Some people notice PMS symptoms here.
Why it varies
Stress, illness, sleep, travel and medication can change timing. See how trackers predict and when to see a doctor.
Remember that a phase chart is a model, not a measurement of your body.