Know where you are in the month

A woman who tracks her cycle knows something about her own body that most of medicine never asks about.

In 1953 John Billings, a neurologist in Melbourne, was asked by a Catholic marriage bureau to find a natural way to know when a woman could conceive. With his wife Evelyn he built a method from something women had always noticed and nobody had written down: the body's own signs change through the month, and you can learn to read them. The Billings method has been studied by the World Health Organization and taught in a hundred countries. In 2013 Alisa Vitti took the same awareness out of the fertility clinic and into daily life in WomanCode: the idea that food, work and training can follow the phases of the month. Her evidence is thinner than the Billings', and I'll say so. The practice underneath both is the key.

The cycle has four phases. The bleed, usually days one to five. The follicular phase, as estrogen rises toward ovulation, when energy and tolerance for intensity tend to climb. Ovulation, around day fourteen in a textbook and anywhere from ten to twenty in a person. And the luteal phase, when progesterone rises, temperature climbs half a degree, and the week before the next bleed carries the mood and appetite changes that have names.

For this month the use is the oldest one: know where you are. A woman who writes the cycle day next to the sleep and the walk will, in three months, hold a map of her own month that no app made for her. That map changes how you plan a hard week, when you push in training, and what you forgive yourself for.

For the men reading this: half the people you love run on this clock. Learning the four phases is not a small courtesy. It's a form of paying attention.