Luteal phase: what happens and how to measure it

The luteal phase is the second half of your menstrual cycle. It runs from the day after ovulation to the first day of your next period. It usually lasts 12 to 14 days and is run by progesterone from the corpus luteum. Whether that phase really happened is something one blood value can show.

Most explanations of the cycle stop at ovulation. I think that is a shame. The real work happens right after it. That work decides whether you feel bloated, sleep badly or can get pregnant.

What is the luteal phase?

The luteal phase starts as soon as the egg has been released at ovulation. The empty follicle then turns into the corpus luteum, the yellow body. That corpus luteum produces progesterone, and progesterone makes the lining of your womb thick and well supplied.

If no fertilised egg arrives, the corpus luteum shuts down after about two weeks. Your period starts.

If a fertilised egg does implant, the embryo makes human chorionic gonadotropin (hCG). That hormone keeps the corpus luteum working, and your period stays away.

Say your ovulation test was positive on day 14 of a 28-day cycle. On day 15 the egg is released. From day 16 your progesterone rises, and around day 21 to 22 it reaches its peak. If there is no fertilisation, progesterone falls from day 26 and your period starts on day 29.

Your next cycle begins on the first day of your period. Your cycle has four phases: menstruation, the follicular phase, ovulation and the luteal phase.

In the follicular phase a follicle matures under follicle-stimulating hormone (FSH). A surge of luteinising hormone (LH) triggers ovulation, and then progesterone takes over. How those four hormones work together is explained in understanding your menstrual cycle hormones.

How long does the luteal phase last?

On average the luteal phase lasts 12 to 14 days. An analysis of 612,613 cycles from app users found a mean of 12.4 days. The range ran from 7 to 17 days.

In an American cohort of women trying to conceive the mean was 14 days. 'About 14 days' is a rounding, not a rule.

What stands out in those 612,613 cycles: almost all the variation sits in the first half. The follicular phase averaged 16.9 days, with a range of 10 to 30 days. The luteal phase stays fairly stable from woman to woman.

Is your cycle 35 days? Then your ovulation usually falls around day 21, not day 14.

That is exactly where the classic mistake lives. Having progesterone drawn on day 21 then often lands you still in the follicular phase. The value is then low without anything being wrong.

In a longer cycle, ovulation and the luteal phase shift later. In a shorter cycle they move earlier. The luteal phase itself barely changes in length.

Luteal phase symptoms: how do you feel in this phase?

During the luteal phase some women feel calmer, others irritable or tired. Progesterone raises your body temperature slightly, can cause bloating and makes your breasts more tender. A few days before your period progesterone and oestrogen fall, and the familiar premenstrual complaints arrive. Most women notice at least one of these changes.

Those hormonal changes are small but measurable. The temperature rise is about 0.2 to 0.5 degrees Celsius. You only notice it if you measure every morning before getting up. The bloating comes from progesterone slowing your gut and your body holding a little more fluid.

Sleep changes during this phase too. Many women sleep more lightly in the week before their period. Cravings for sweet or salty food increase.

That is not a lack of discipline. It is progesterone setting your metabolism a fraction higher.

Complaints that come back every month and genuinely limit you belong to PMS. What is going on then is covered in PMS symptoms and what helps. If work and relationships suffer, it may be PMDD, more than ordinary PMS.

One thing I want to set straight here. Complaints in the second half of your cycle do not prove there was an ovulation. Your body makes hormones without ovulation too, and you can feel bloated and irritable then as well.

Short luteal phase: when is short too short?

A luteal phase that lasts 11 days or less counts as short. You count from the day of ovulation. An American study followed 284 women aged 30 to 44. It occurred in 18 percent of their 1,635 cycles.

In the following cycle the chance of pregnancy was slightly lower, 0.82 times as high. After twelve months of trying there was no difference any more.

So one short luteal phase is no reason to panic. It happens in almost one in five cycles. The effect on the chance of pregnancy was small and temporary. Women who smoked had a short luteal phase more often in that study.

Researchers do name a deficient luteal phase as a possible cause of infertility and miscarriage. At the same time they write that no good test exists for such a luteal phase defect. A low progesterone value on one day is a clue, not a diagnosis.

A long luteal phase, longer than 17 days, is rare. Does your period stay away that long after a confirmed ovulation? Then think of a possible pregnancy first.

It often turns out to be a counting error. Ovulation came later than the ovulation test or the app suggested.

A regular cycle is not proof of ovulation

This is the point that almost no explanation of the luteal phase makes. A Norwegian population study followed 3,168 women with a normal cycle length. Each woman had one random progesterone value drawn in the second half of the cycle.

In 37 percent it was below 9.54 nmol/L. That was the threshold the researchers used for ovulation. So more than one in three normal-looking cycles probably had no real luteal phase.

Picture two women with a 28-day cycle, both drawn on day 21. One reads 40 nmol/L, the other 4 nmol/L. From the outside their cycles were identical.

One measurement on one day is still a snapshot. The study did not follow a series of cycles per woman. Some of the low values may come from the draw day.

But the core stands. A regular period, an app that reports 'ovulation' and premenstrual complaints do not prove ovulation.

The Dutch GP guideline on subfertility is the NHG-standaard Subfertiliteit. It assumes no ovulation disorder at a cycle of 21 to 35 days. It then advises the GP not to measure progesterone. That is a defensible choice for a consulting room where time and budget are limited.

I think you are entitled to know that the assumption exists. And that it can be checked.

How to measure your luteal phase with a blood test

The direct measure of the luteal phase is progesterone in your blood. You draw it about seven days after ovulation. That is when the corpus luteum is at its peak.

In a 28-day cycle that is around day 21. In a longer cycle the draw day shifts with it. A value well above the laboratory threshold fits an ovulation. A low value first asks for a repeat on a better day.

Do not know your ovulation day? Then count seven days from a positive LH test. Or count seven days back from the day you expect your period. What an LH test does and does not tell you is in LH levels and your cycle.

The step-by-step of such a measurement is in confirming ovulation with a blood test. The values laboratories use per cycle phase are in the progesterone reference values table. The page on progesterone as a blood value explains what the hormone is.

At Lunara you have that value measured with the progesterone test. You pick a draw day yourself and have blood taken at a collection point near you. The result arrives digitally.

A result gives a number on one day, not a verdict on your fertility. Discuss a low or unexpected value with your GP.

My concrete advice is small. Mark the day of your positive LH test or the day after your temperature jump. Count seven days. That is the day on which a progesterone value says the most about your luteal phase.

Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.

Sources

1. Bull JR, Rowland SP, Scherwitzl EB, Scherwitzl R, Danielsson KG, Harper J. Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. NPJ Digit Med. 2019;2:83. PMID 31482137.
2. Crawford NM, Pritchard DA, Herring AH, Steiner AZ. Prospective evaluation of luteal phase length and natural fertility. Fertil Steril. 2017;107(3):749-755. PMID 28065408.
3. Prior JC, Naess M, Langhammer A, Forsmo S. Ovulation prevalence in women with spontaneous normal-length menstrual cycles: a population-based cohort from HUNT3, Norway. PLoS One. 2015;10(8):e0134473. PMID 26291617.
4. Mesen TB, Young SL. Progesterone and the luteal phase: a requisite to reproduction. Obstet Gynecol Clin North Am. 2015;42(1):135-151. PMID 25681845.
5. NHG. NHG-standaard Subfertiliteit (Dutch GP guideline on subfertility). Consulted 2026.