Lesson 2 - Understanding Cycle Phases and How to Chart BBT


  • Identify and understand the four phases of the menstrual cycle.
  • Learn how charting BBT can help you determine where you are in your menstrual cycle and your proximity to ovulation.

Major Points:

  • The menstrual cycle consists of four main phases: menses, follicular phase, ovulation, and luteal phase.
  • Ovulation occurs once a month and divides the follicular phase (occurs before ovulation) and the luteal phase (occurs after ovulation).
  • The length of the follicular phase determines the cycle length. This phase can vary in women and from cycle to cycle.
  • The luteal phase is typically the same length and rarely changes by more than one to two days each cycle.
  • In most women, the luteal phase lasts 12 to 14 days. In some instances, it can last 10 to 16 days.
  • Conception is most likely just before or during ovulation.

The menstrual cycle is a series of phases that your body experiences once a month to prepare for a possible pregnancy. Learning about these phases is important so that you’re better equipped to identify fertility signs that indicate how close you are to ovulation. On average, a woman’s menstrual cycle will last 21 to 35 days. The cycle begins on the first day of your period.

Cycle Phases:

  • Menses Phase: This phase begins on the first day of menstruation and typically lasts until the 5th day of your cycle. During the menstrual phase, the uterus sheds soft tissue and blood vessels from its inner lining. On average, 10 ml to 80 ml of blood exits through the vagina. You are typically not fertile during the menstrual phase.
  • Follicular Phase: The follicular stage also begins on the first day of menstruation but doesn’t end until around day 13, or when ovulation starts. During the follicular phase, the pituitary gland releases a hormone that stimulates egg cells to grow in the ovaries. One egg cell will mature into a follicle. Once matured, the follicle secretes a hormone to stimulate the uterus to develop endometrium, a lining of blood vessels and soft tissues.
  • Ovulation Phase: Around the 14th day of your cycle, ovulation occurs. The pituitary gland secretes the luteinizing hormone (LH) that causes the release of the matured egg cell from the ovary. The egg cell then travels to the fallopian tube with the help of the cilia of the fimbriae, finger-like projections located at the end of the fallopian tube.
  • Luteal Phase: The luteal phase begins around day 15 and lasts until the end of your cycle. During this phase, the egg cell stays in the fallopian tube for 24 hours. If a sperm cell fails to impregnate the egg during this time, the egg cell disintegrates. When the hormone used to retain the endometrium runs out, a new menstrual cycle begins.

Once you can identify the different menstrual phases, you can begin charting your basal body temperature (BBT). Charting can help you determine when you ovulate each month and the best time to have sex if you’re trying to conceive. Your BBT refers to your body’s temperature while at rest. Your temperature rises when you ovulate due to the secretion of progesterone. 

To determine your basal body temperature, you must take your temperature in the morning before getting out of bed. It’s important to chart at the same time each day, preferably within a 30-minute window. Charting your BBT is a simple and inexpensive way to track ovulation. Today you can find numerous free or cheap fertility charting apps and programs that make BBT tracking easy to boost your odds of conception.