The luteal phase is the second half of the menstrual cycle, spanning from ovulation to the start of your next period. It typically falls between days 15 and 28 of a standard 28-day cycle and lasts an average of 12 to 14 days. Its main purpose is preparing the uterine lining for a possible pregnancy.
Where It Falls in the Cycle
The menstrual cycle has two main halves, separated by ovulation. The first half, called the follicular phase, begins on the first day of your period and continues until an egg is released from the ovary. The luteal phase begins immediately after ovulation and ends when your next period starts. If your cycle is 28 days long, ovulation typically happens around day 14, placing the luteal phase on roughly days 15 through 28.
The follicular phase can vary quite a bit in length from person to person and cycle to cycle, which is why periods don’t always arrive on schedule. The luteal phase, by contrast, tends to stay relatively consistent for each individual. A normal luteal phase lasts anywhere from 10 to 17 days, with most people falling in the 12 to 14 day range.
What Happens During the Luteal Phase
Once the ovary releases an egg, the empty follicle that housed it transforms into a temporary structure called the corpus luteum. This structure has one critical job: producing progesterone, the hormone that thickens and enriches the uterine lining so it can support an embryo. The corpus luteum also produces some estrogen, but progesterone is the dominant hormone of this phase.
If sperm fertilizes the egg and conception occurs, the corpus luteum keeps producing progesterone for about 12 weeks. Around that point in the first trimester, the placenta takes over hormone production and the corpus luteum is no longer needed. If fertilization doesn’t happen, the corpus luteum begins to break down about 10 days after ovulation. Progesterone levels drop, the thickened uterine lining can no longer sustain itself, and your period begins, restarting the cycle.
How You Can Tell You’re in It
The most reliable physical marker of the luteal phase is a slight rise in basal body temperature. After ovulation, your resting temperature increases by less than half a degree Fahrenheit (about 0.3°C). This small shift stays elevated throughout the luteal phase and drops back down when your period arrives. Tracking this temperature change each morning before getting out of bed is one of the oldest methods for confirming that ovulation has occurred.
Progesterone is also behind many of the physical sensations you may notice in the second half of your cycle: breast tenderness, bloating, fatigue, mood changes, and food cravings. These are essentially the same symptoms associated with PMS, and that’s no coincidence. PMS symptoms are driven by the hormonal shifts of the luteal phase, particularly the rise and then sharp fall of progesterone in the days before your period.
Why Luteal Phase Length Matters for Fertility
The luteal phase needs to be long enough for the uterine lining to thicken and for an embryo to implant. A luteal phase shorter than 10 days is considered too short. In that scenario, progesterone drops and menstruation begins before the lining has had time to fully develop, making it difficult for a pregnancy to take hold even if an egg was fertilized.
This condition is sometimes called luteal phase deficiency. It’s generally defined as a luteal phase lasting 10 days or fewer, often combined with low progesterone levels during the middle of that phase. In normal ovulatory cycles, about 31% of cycles have mid-luteal progesterone levels below 10 ng/mL, and roughly 8% fall below 5 ng/mL. When both a short phase and low progesterone occur together, the uterine lining may not develop the changes needed to support implantation.
If you’re trying to conceive and consistently have very short cycles or spotting that starts well before your expected period, tracking your luteal phase length can provide useful information to share with a healthcare provider. Knowing whether your luteal phase is consistently under 10 days helps narrow down one possible barrier to conception.
The Luteal Phase During Early Pregnancy
When conception does occur, the luteal phase doesn’t simply end. Instead of breaking down, the corpus luteum receives a hormonal signal from the developing embryo that keeps it alive and producing progesterone. This sustained progesterone production is what prevents your period from arriving. It’s also why early pregnancy symptoms, like breast soreness and fatigue, feel so similar to PMS: the same hormone is responsible for both.
The corpus luteum remains the primary source of progesterone until roughly week 12 of pregnancy, when the placenta is mature enough to take over. This handoff is sometimes called the luteal-placental shift, and it’s a critical transition in early pregnancy support.