When is cortisol highest? Your daily cortisol rhythm

Cortisol is highest in the early morning and lowest around midnight. That daily swing is one of the largest in the human hormone system, so it shapes how a cortisol result is read. A value that is ordinary at 11 p.m. can look very different at 8 a.m.

This page explains the pattern, what shifts it, and what it means when you are deciding when to test.

Cortisol AM and PM

A morning result and a later one, because cortisol changes through the day. Follow the times on your lab order.

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The pattern across 24 hours

Here is the usual shape in a healthy adult who sleeps at night, drawn from three reviews (Endocrine Reviews, 2024; Int J Mol Sci, 2025; Endocrine Reviews, 2017).

• About 4 a.m.: cortisol starts to rise during the latter part of sleep.
• Around waking: the rise continues and reaches the daily peak. One review gives about 7 to 8 a.m., with the top reached within 30 to 45 minutes of waking. Another says the peak comes within 3 hours of waking. Both fit the same idea: the peak is tied to when you wake.
• Daytime: levels decline steadily. Some studies report a small second rise in the early to mid afternoon, between about 2 and 4 p.m. It is subtle.
• Evening: cortisol keeps falling toward its lowest levels.
• Around midnight: the low point, called the nadir. A 2017 review notes that at this time cortisol can sit close to the limit of what routine assays can detect.

The 2017 review makes a point worth remembering. Morning peak values are often within the range that would count as unusual for the afternoon or evening. The same number can be normal at one hour and noteworthy at another.

Short pulses on top of the daily curve

The smooth curve hides something. Cortisol is released in pulses, roughly every 1 to 2 hours, and the daily rhythm is built from them (Endocrine Reviews, 2024). The pulses are large during waking hours and small during the early hours of sleep (Endocrine Reviews, 2017).

For readers, the point is simple. A single reading is a snapshot of a moving signal. The 2024 review says the variation with time of day makes a single value taken at a random time hard to interpret.

What sets and shifts the rhythm

The master clock sits in a part of the hypothalamus called the suprachiasmatic nucleus. Light is its strongest cue. Sleep timing, meals, activity and stress also play a part (Int J Mol Sci, 2025). A few points follow from the reviews:

• Sleep. Falling asleep lowers HPA axis activity, so cortisol is low in the first half of the night. In the second half, when REM sleep predominates, HPA activity increases. Sleep and cortisol influence each other in both directions (Endocrine Reviews, 2024).
• Age. The daily swing gets smaller with age. The lowest point rises, and the early-morning rise starts earlier. Age-specific cut-offs are typically not used in practice.
• Sex. The same review reports that men have a higher average peak, nadir and morning rise than women before menopause. It adds that the difference in the peak is no longer seen after menopause.
• Meals and exercise. Both can cause short-term rises on top of the curve. A 2017 review describes a short rise after a carbohydrate-rich meal under controlled conditions, and a brief rise after exercise.
• Shift work and jet lag. The 2024 review says sudden changes to the sleep-wake cycle, such as shift work or jet lag, activate the HPA axis and alter the normal cortisol pattern. Some chronic shift workers, but not all, have a delayed early-morning rise. A 2025 review discusses cortisol as a possible marker of circadian disruption, but that is research. It isn’t a clinical test for a body-clock problem.

The sharp rise in the first hour after waking has its own name, the cortisol awakening response. See the cortisol awakening response page.

What this means for testing

MedlinePlus says blood samples are usually taken twice in a day: once in the morning, when cortisol is normally highest, and again around 4 p.m., when it is normally much lower. Doing both shows whether the level falls the way it usually does. Our AM and PM timing page covers the practical side.

One published set of figures for blood (serum) cortisol shows how far the level falls. A 2025 review gives 3 to 23 µg/dL at 8 a.m. and 3 to 13 µg/dL at 4 p.m. for total serum cortisol (Int J Mol Sci, 2025). Other sources give different figures, because labs and methods differ. Use the range printed on your own report, and see normal cortisol levels for more. If your report is in nmol/L, the cortisol units converter can help.

The seller’s page for its morning-and-later test gives typical collection windows. It is unclear about when the second sample is taken, and it doesn’t say whether the test is one visit or two. Check that before you order, and follow the timing on your lab order. The page states no fasting rule either, so follow the instructions on your order.

Questions people ask

Is it a problem if my cortisol is low in the morning?

On its own, a morning result under your lab’s range is not a diagnosis. It is a reason to talk to a clinician, who will look at it next to your symptoms, any medicines and how the sample was taken. MedlinePlus says the most common cause of an abnormal cortisol result is taking steroid medicines for a long time, or stopping them suddenly, and that stress, pregnancy, exercise, temperature extremes and some medicines such as birth control pills can also change results. A single blood cortisol can’t diagnose or rule out adrenal insufficiency. If you take a steroid medicine, ask your prescriber how it affects your results, and don’t change it yourself. See low cortisol.

Is it a problem if cortisol is high in the morning?

Morning is when high values are expected. A value that looks high for the afternoon can be ordinary at 8 a.m. A single blood cortisol can’t diagnose or rule out Cushing’s syndrome either. Tests clinicians use for it include late-night saliva, a 24-hour urine collection and a dexamethasone suppression test, and they belong with a clinician.

When is cortisol lowest?

Around midnight, in people who sleep at night. It is also low in the first part of sleep. That low is normal and is part of the pattern.

Does the pattern change if I work nights?

Cortisol follows your internal clock and your sleep and wake timing. A 2022 laboratory study found the rise after waking is larger when waking happens at an earlier point in the body clock, and suggested this could matter for shift workers who wake at unusual body-clock times (Front Neurosci, 2022). That is research in small groups. If you work nights, tell the clinician or lab, so the time of your sample is read against your own schedule.

Keep reading

• Cortisol awakening response

  The rise in the first hour after waking and how it is measured.

• AM and PM timing

  When the samples are taken and why timing matters.

• Normal cortisol levels

  Published ranges by time of day, with sources.

• What cortisol does

  The jobs behind the rhythm.