Luteal Phase

The luteal phase is the second half of a menstrual cycle, running from ovulation to the start of the next period. It typically lasts twelve to fourteen days.

Its usefulness comes from being the stable half. The follicular phase, from the start of a period to ovulation, varies a great deal both between people and from cycle to cycle, while the luteal phase stays close to the same length in the same person. That is why every cycle estimate works backward from the expected period rather than forward from the last one: subtract fourteen days from the next period and you have an estimate of ovulation.

It is also the phase in which basal body temperature sits at its higher plateau, which is how a chart confirms that ovulation happened.

What it is not

Fourteen days is a population average, not your number. A real luteal phase runs anywhere from about ten to sixteen days, and anyone whose own phase is at either end of that will find the standard estimate consistently wrong. A phase shorter than about ten days is worth raising with a doctor.

Where you see it in FitnessSyncer

Logging your cycles in the Notebook, or connecting a service that records them, builds predictions from your own recorded history rather than from a 28-day average; see cycle tracking. Our period and fertile window estimator uses the generic fourteen-day assumption and says so.