The luteal phase is the second half of your menstrual cycle, spanning from ovulation to the start of your next period. It typically lasts 12 to 14 days, beginning around day 15 of a 28-day cycle. During this window, your body undergoes a coordinated series of hormonal and physical changes designed to prepare for a possible pregnancy.
How the Luteal Phase Begins
The moment you ovulate, the follicle that released the egg doesn’t just disappear. It transforms into a temporary hormone-producing structure called the corpus luteum. This small cluster of cells on the ovary becomes a progesterone factory, pumping out the hormone that dominates the entire second half of your cycle. It also produces smaller amounts of estrogen.
Progesterone is the defining hormone of the luteal phase. Nearly every change you experience during these two weeks, from shifts in body temperature to changes in mood and appetite, traces back to this single hormone and the way your body responds to it.
What Happens Inside Your Uterus
The most important job of the luteal phase is remodeling the uterine lining into a hospitable environment for a fertilized egg. Under the influence of progesterone, the endometrium thickens and its glands begin secreting nutrients and fluids. These glands coil and branch as they extend through the tissue, forming a complex network that can nourish an embryo in the earliest days before a placenta develops. New blood vessels grow into the lining to supply it with oxygen and nutrients.
This transformation is so distinct that doctors call it the “secretory phase” of the endometrium, in contrast to the “proliferative phase” earlier in your cycle when the lining was simply growing thicker under estrogen’s influence. By the middle of the luteal phase, the lining is at its most receptive to implantation.
Your Body Temperature Rises
Progesterone acts on the brain’s temperature control center, raising your core body temperature by 0.3°C to 0.7°C (roughly 0.5°F to 1.3°F) compared to the first half of your cycle. This shift is subtle enough that you won’t notice it day to day, but it’s consistent enough that tracking your basal body temperature each morning can confirm whether ovulation occurred. The temperature stays elevated throughout the luteal phase and drops again when your period starts, or stays high if you become pregnant.
Mood, Energy, and Appetite Changes
Progesterone doesn’t just act on your uterus. Your body converts some of it into a compound that interacts with the same brain receptors targeted by anti-anxiety medications and sedatives. This compound enhances the effect of your brain’s primary calming chemical, which is why many people feel more relaxed, sleepy, or slightly sluggish during the luteal phase. In most people, this produces mild, manageable shifts in mood and energy.
For a smaller group, the brain’s receptors don’t respond normally to these fluctuations. Instead of a calming effect, the hormonal shifts trigger irritability, anxiety, or depressed mood. This abnormal response is at the root of premenstrual dysphoric disorder (PMDD), a condition that goes well beyond typical PMS.
Your metabolism also picks up. Resting energy expenditure increases by about 6% during the late luteal phase compared to the first half of the cycle. That translates to roughly 100 to 150 extra calories burned per day for most people, which helps explain the increased appetite and food cravings that often show up in the days before your period.
What Happens If You Don’t Get Pregnant
The corpus luteum appears to have a built-in lifespan. If no embryo implants in the uterine lining, the corpus luteum begins to break down on its own after about 10 to 14 days, a process called luteolysis. Interestingly, the exact mechanism that triggers this breakdown isn’t fully understood. Research in primates has shown that the process isn’t simply caused by a drop in signals from the brain; even when those signals are temporarily removed and then restored, progesterone production bounces back. Something within the corpus luteum itself seems to set its expiration date.
As progesterone levels fall, the thickened uterine lining loses its hormonal support. The blood vessels that grew into the lining constrict, the tissue breaks down, and menstruation begins. The spent corpus luteum gradually shrinks into a small, pale scar on the ovary. And with the drop in progesterone, the cycle resets: your temperature falls, your mood and energy shift again, and the brain signals that recruit a new follicle ramp back up.
What Happens If You Do Get Pregnant
When a fertilized egg implants in the uterine lining, the early embryo immediately begins releasing a hormone called hCG (the same hormone detected by pregnancy tests). hCG acts on the same receptor as the brain signal that originally maintained the corpus luteum, essentially taking over the job and keeping progesterone production running. This prevents the lining from breaking down and stops menstruation from occurring.
The corpus luteum continues producing progesterone for roughly the first 8 to 10 weeks of pregnancy, until the placenta is developed enough to take over hormone production on its own.
When the Luteal Phase Is Too Short
A luteal phase of 10 days or fewer is considered short, a condition sometimes called luteal phase deficiency. The concern is that a shorter window may not give the uterine lining enough time to develop properly for implantation. Some definitions set the cutoff at 9 days, others at 11, which reflects how much debate surrounds the diagnosis.
Despite the logical concern, the American Society for Reproductive Medicine notes that the available evidence does not support luteal phase deficiency as a proven, independent cause of infertility or recurrent pregnancy loss. In studies, people with shorter luteal phases were less likely to conceive in any given month, but their overall chances of pregnancy over 12 months were not lower than average. This doesn’t mean a short luteal phase is irrelevant, but it does mean the relationship between luteal phase length and fertility is more nuanced than it might seem.
If you’re tracking your cycles and consistently see fewer than 10 days between ovulation and your period, it’s worth discussing with a reproductive health provider, particularly if you’re trying to conceive.