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Reproductive Health

Progesterone

Progesterone is the hormone that prepares the body for pregnancy. It naturally rises in the second half of your monthly cycle, after an egg is released, and falls again if pregnancy does not happen. Because it only climbs after that release, the test is timed to your cycle — usually around day 21 of a 28-day one — so your result is read against where you are in your cycle.

Targeted Testing
CategoryReproductive Health
Reference rangeSee your report
Evidence○Targeted Testing
Last updated3 July 2026
On this page

What is progesterone?

Progesterone is a steroid hormone — a chemical messenger the body makes from cholesterol. Its main role is to help prepare the body for pregnancy, working alongside other female hormones. After ovulation (when an egg is released from the ovary), a small temporary structure called the corpus luteum forms at the site where the egg was released. The corpus luteum begins producing progesterone, which acts on the uterine lining — the endometrium — stopping it from growing and instead preparing it for the possible implantation of a fertilised egg. If pregnancy does not occur, the corpus luteum breaks down, progesterone falls, and the lining sheds as a period. If pregnancy does occur, progesterone continues to rise and supports the early pregnancy. Oestrogen and progesterone together, released by the ovaries, are the two main hormones responsible for the female reproductive cycle and the development of female body characteristics.

Why is it tested?

Progesterone is most useful as a test of whether ovulation has occurred. Because it is only produced in significant amounts after an egg is released, measuring it at the right point in the cycle can confirm whether ovulation happened that month. Multiple measurements across the cycle can also help investigate fertility concerns. The test is timed carefully: for a 28-day cycle, the sample is taken about seven days before the expected period — typically around day 21. If your cycle is longer or shorter, the timing shifts accordingly. A sample taken at the wrong cycle point is hard to interpret, so your GP will ask when your last period started.

Reference range (Australia)

No single 'normal' value — progesterone rises in the second half of the menstrual cycle; a mid-luteal sample (timed to about seven days before the next expected period) is used to confirm ovulation, read against your report's interval nmol/L

Progesterone is very low in the first half of the cycle (follicular phase) and rises after ovulation (luteal phase). The test is timed to the mid-luteal phase — about day 21 of a 28-day cycle, or approximately seven days before the next expected period. Levels during pregnancy are substantially higher. Always use the interval printed on your own report for your cycle phase.

Reference intervals vary between laboratories. Always use the range printed on your own report.

What your result means

If your level is low

If you are testing because you are trying to conceive, a single low day-21 result is one of the most common reasons for a needless scare. It very often just means the sample was taken on the wrong day, before progesterone had risen. It can also mean ovulation did not happen that month, or the corpus luteum is making less hormone than expected. Either way, one result is not a diagnosis, and your GP will look at the timing and your cycle pattern before drawing any conclusion.

If your level is in range

A result within the phase-appropriate reference interval for your cycle day suggests progesterone is rising as expected after ovulation. Cycle timing is always the most important context for interpreting this result.

If your level is high

A progesterone result above the expected threshold in the mid-luteal phase (the second half of the cycle, around day 21) indicates that ovulation has occurred and the corpus luteum is functioning. This is a reassuring finding if you are investigating whether your cycle is ovulatory. Your GP will look at this alongside your cycle history and any other symptoms.

What can affect your result

Cycle phase and timing are the dominant factors. Progesterone is very low in the follicular phase (the first half of the cycle, before ovulation) and rises substantially only after the egg is released. The timing of the blood draw — whether it falls in the right mid-luteal window — has the greatest effect on what the result means. If ovulation does not occur (an anovulatory cycle), progesterone will stay low throughout the month. Hormonal contraceptives that prevent ovulation — the pill, implant, or injection — also suppress the post-ovulatory rise. Stress, significant weight changes, and intense exercise can disrupt ovulation and keep progesterone low. During pregnancy, progesterone is produced first by the corpus luteum and then by the placenta, reaching levels much higher than in a non-pregnant cycle.

When to act

If your progesterone result is lower than expected for your cycle day, it is worth discussing with your GP — and the timing of your sample is one of the first things they will ask about. A single result is rarely the whole story. If you are investigating ovulation or fertility, your GP may suggest repeat testing in a subsequent cycle to build a clearer picture. This page is general information and is not a substitute for advice from your GP.

Frequently asked questions

Progesterone's main role is to prepare the body for a possible pregnancy after ovulation. After an egg is released, a small structure called the corpus luteum forms in the ovary at the release site and begins producing progesterone. This progesterone acts on the uterine lining — called the endometrium — preparing it for the possible implantation of a fertilised egg. If pregnancy does not occur, the corpus luteum breaks down, progesterone falls, and the lining sheds as a period. Alongside oestrogen, progesterone regulates the full menstrual cycle.

Progesterone rises after ovulation and peaks in the mid-luteal phase — the middle of the second half of the cycle. For a standard 28-day cycle this is around day 21, which is approximately seven days before the next expected period. Testing at this point captures progesterone when it should be at its highest if ovulation occurred. If your cycle is longer or shorter, the ideal day shifts — your GP will calculate the right timing for you.

A mid-luteal progesterone result can indicate whether ovulation occurred in that cycle. A level that rises substantially by about day 21 (of a 28-day cycle) indicates ovulation is likely to have occurred that month, which your GP reads with your cycle history. Multiple measurements across cycles can also help investigate whether ovulation is occurring regularly, because levels vary predictably through the menstrual cycle.

After ovulation, the corpus luteum — the temporary structure that forms in the ovary — produces progesterone that prepares the uterine lining for a fertilised egg to implant. If fertilisation occurs, progesterone continues to rise and supports the early pregnancy. Later in pregnancy, the placenta takes over progesterone production. Progesterone is sometimes measured in early pregnancy alongside other tests as part of routine care. What any result means depends on the full clinical picture, which your GP or obstetric team can explain.

There is no single normal number — progesterone changes dramatically across the menstrual cycle. Levels are very low in the first half of the cycle, then rise substantially after ovulation. The reference interval on your report is specific to your cycle phase and your laboratory. Your GP will interpret your result in the context of the cycle day the sample was taken.

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