The luteal phase, and why we anchor on it

The luteal phase runs from ovulation to your next period. Unlike the follicular phase, it's relatively stable — usually about 12 to 14 days for a given person.

That stability is useful: instead of back-calculating from a guessed ovulation day, we anchor your next-period prediction on your observed luteal length once we can measure it.

A luteal phase shorter than about 10 days is sometimes linked with difficulty conceiving, which is why we flag it for a conversation with a clinician.