The luteal phase is the second half of your menstrual cycle, starting the day after you ovulate and ending when your period begins. It typically lasts between 10 and 15 days, and its primary job is preparing your uterine lining for a potential pregnancy. If no pregnancy occurs, the phase ends with the shedding of that lining, which is your period.
What Happens During the Luteal Phase
Once an egg is released from your ovary, the empty follicle it left behind transforms into a temporary structure called the corpus luteum. This small cluster of cells starts producing high amounts of progesterone, along with some estrogen. Progesterone is the dominant hormone of this phase, and it has one main goal: thickening and enriching the uterine lining so a fertilized egg could implant there.
If no embryo implants, the corpus luteum gradually breaks down. As it degenerates, progesterone and estrogen levels drop sharply. That hormonal withdrawal triggers the shedding of the uterine lining, and your period starts. The luteal phase is over, and a new cycle begins.
How It Differs From the First Half of Your Cycle
Your cycle has two main halves. The first, called the follicular phase, runs from the start of your period until ovulation. During this stretch, your body is selecting and maturing an egg inside a follicle. The follicular phase is the part of your cycle that varies most in length, both from cycle to cycle and across your lifetime. That’s why cycles can be 25 days one month and 32 the next.
The luteal phase, by contrast, is relatively consistent. Most people’s luteal phases stay close to the same number of days each cycle. So when your overall cycle length changes, it’s almost always because the first half got shorter or longer, not the second.
Common Symptoms You Might Notice
The surge in progesterone after ovulation is responsible for many of the physical changes you feel in the days before your period. Progesterone raises your basal body temperature by a small but measurable amount, typically between 0.4°F and 1°F. This temperature shift is one of the most reliable signs that ovulation has occurred, and it stays elevated throughout the luteal phase until your period arrives.
Progesterone also causes breast tenderness, bloating, mood changes, fatigue, and food cravings. These are the symptoms commonly grouped under PMS, and they happen specifically because of the hormonal environment of the luteal phase. As progesterone and estrogen decline in the final days before your period, those symptoms often intensify before resolving once bleeding starts.
The Luteal Phase and Fertility
The length of your luteal phase matters for conception. After a fertilized egg travels down the fallopian tube, it needs to implant in the uterine wall. In humans, this typically happens between days 8 and 12 after ovulation. If your luteal phase is too short, the uterine lining may start shedding before an embryo has a chance to implant.
A luteal phase shorter than 10 days is generally considered a potential concern, a condition sometimes called luteal phase deficiency. The American Society for Reproductive Medicine defines it as a luteal phase of 10 days or fewer, measured from the hormonal surge that triggers ovulation to the onset of menstrual bleeding. If you’re tracking your cycles and consistently see fewer than 10 days between ovulation and your period, that’s worth discussing with a provider, especially if you’re trying to conceive.
What Happens If You Get Pregnant
When an embryo successfully implants, it begins producing a hormone called hCG (the same hormone pregnancy tests detect). This hormone is structurally similar to the brain signal that originally triggered ovulation, and it sends a direct message to the corpus luteum: keep going. Instead of breaking down, the corpus luteum continues producing progesterone, which maintains the uterine lining and supports the early pregnancy.
The corpus luteum stays active until roughly 10 weeks of pregnancy. By that point, the placenta has developed enough to take over progesterone production on its own. This handoff is why the first trimester is sometimes considered the most hormonally fragile period of pregnancy.
How to Track Your Luteal Phase
The simplest method is tracking your basal body temperature each morning before getting out of bed. You’ll see a small but consistent rise after ovulation, and the number of days between that rise and the start of your next period is your luteal phase length. Ovulation predictor kits, which detect the hormonal surge that precedes egg release, offer another way to pinpoint when the luteal phase begins.
Because the luteal phase is the more stable half of your cycle, knowing its length helps you predict your period more accurately than counting from day one alone. If your luteal phase is consistently 13 days, for example, and you detect ovulation on a given day, you can reasonably expect your period about 13 days later. This is also the principle behind many fertility awareness methods of family planning.