Cortisol Normal Levels: Reference Ranges by Time of Day
Last updated: May 2, 2026
Cortisol is the body's primary stress hormone, secreted by the adrenal cortex and essential for blood sugar, blood pressure, immunity, and metabolism. When a lab report shows your cortisol value, the natural question is: what counts as normal? This guide reviews reference ranges by time of day, the differences between blood, saliva, and urine tests, and how to read your results responsibly.
Table of contents
1. Why cortisol reference ranges matter
Cortisol is a steroid hormone secreted by the adrenal cortex that influences blood sugar, blood pressure, immune function, and metabolism. Persistent values outside the reference range may point to endocrine conditions such as Cushing's syndrome (excess) or Addison's disease and adrenal insufficiency (deficiency).
Chronic stress and disrupted sleep can also flatten or invert the natural diurnal rhythm. Knowing the reference ranges helps you interpret a lab report and decide whether further evaluation is appropriate.
- Screening for endocrine conditions (Cushing's, adrenal insufficiency)
- Objective lens on stress and circadian rhythm disruption
- Context for sleep, fatigue, and mood concerns
2. General cortisol reference ranges
Cortisol does not have a single "normal" number. Values vary with the time of sampling and the assay used because cortisol follows a strong diurnal pattern, peaking shortly after waking and bottoming out around midnight.
The table below shows approximate reference ranges. Each laboratory publishes its own ranges — always cross-check with the values printed on your report.
| Time | Serum (μg/dL) | Saliva (ng/mL) |
|---|---|---|
| Early morning (6–10 AM) | 6–23 | 0.04–0.56 |
| Midday (12–2 PM) | 5–15 | 0.03–0.30 |
| Late afternoon (4–6 PM) | 3–10 | 0.02–0.20 |
| Late night (10 PM–12 AM) | Usually < 5 | 0.01–0.09 |
μg/dL applies to serum; saliva is reported in ng/mL or nmol/L. Always check the reference range printed on your own lab report.
3. Morning cortisol (peak window)
Cortisol peaks shortly after waking, a phenomenon known as the cortisol awakening response (CAR). Levels typically rise an additional ~50% in the 30–45 minutes after waking.
Common reference ranges for early-morning serum cortisol are 6–23 μg/dL, although some laboratories report 5–25 μg/dL.
When morning cortisol is high
Acute stress, sleep deprivation, intense early-morning training, or pregnancy can transiently elevate values. Persistently high results merit evaluation for Cushing's syndrome and other endocrine causes.
When morning cortisol is low
Low morning cortisol may indicate adrenal insufficiency. Symptoms such as severe fatigue, anorexia, low blood pressure, or hypoglycemia warrant prompt evaluation, often including an ACTH stimulation test.
4. Evening / night cortisol (trough window)
Cortisol falls to its lowest level around 10 PM to midnight. Late-night serum cortisol below 5 μg/dL is typical, and late-night salivary cortisol is a key screening test for Cushing's syndrome.
Cortisol that fails to drop in the evening has been associated with sleep onset difficulty, frequent awakenings, and reduced sleep quality. Sleep hygiene, stress management, and avoiding late caffeine are common starting points.
- Persistently elevated late-night cortisol: refer to endocrinology
- Late-night salivary cortisol is a useful, non-invasive screen
- Improving rhythm: stable sleep schedule, dim evening light, earlier dinner
5. Saliva vs blood vs urine testing
Three test methods are commonly used to evaluate cortisol: serum (blood), saliva, and 24-hour urine. Each captures a different facet of the hormone's biology and is selected based on the clinical question.
Blood is widely used in routine and endocrine clinics; saliva is well-suited to assessing the diurnal rhythm and late-night screening; 24-hour urine cortisol estimates total daily secretion.
| Test type | Strengths | Limitations |
|---|---|---|
| Blood (serum) cortisol | Standard reference, widely available | Stress of venipuncture can transiently elevate values |
| Salivary cortisol | Non-invasive, reflects biologically active free cortisol | Strict collection technique required |
| 24-hour urinary free cortisol | Captures total daily output | Requires careful 24-hour collection |
6. Interpreting high vs low results
A single value above or below the reference range is rarely diagnostic on its own. Physicians integrate symptoms, history, ACTH, DHEA-S, and dynamic testing before drawing conclusions.
Common reasons for high cortisol
Chronic stress, vigorous exercise immediately before sampling, acute illness, exogenous steroid use, and Cushing's syndrome. A flattened or inverted diurnal rhythm is a particularly important pattern.
Common reasons for low cortisol
Primary adrenal insufficiency (Addison's), secondary adrenal insufficiency, post-steroid suppression, and hypopituitarism. Symptoms such as severe fatigue, low blood pressure, and hyperpigmentation should prompt urgent evaluation.
Borderline values
When a value sits at the edge of the reference range, your physician may order a repeat test or a dynamic test such as a dexamethasone suppression test or ACTH stimulation test. Sleep, recent caffeine, and prior 24-hour activity all factor into interpretation.
For more on low values, see Low cortisol symptoms & causes.
7. When to consider testing
The following situations are common reasons clinicians test cortisol. Self-assessment is not a substitute for medical advice — start with your primary physician or an endocrinologist.
- Severe persistent fatigue lasting 3+ months
- Unexplained central weight gain or rapid weight loss
- New high or low blood pressure
- Skin hyperpigmentation, easy bruising, or thinning skin
- Long-standing mood changes, depression, or insomnia
- Symptoms after long-term steroid use
- Menstrual irregularity or sexual dysfunction
For everyday stress self-care, see How to reduce cortisol and Ashwagandha benefits.
8. Frequently asked questions
Which reference range should I trust?
The range printed on your own laboratory report. A common starting reference for early-morning serum cortisol is 6–23 μg/dL, though some labs use 5–25 μg/dL.
Is it normal for morning and evening values to differ?
Yes — a strong diurnal rhythm with morning peaks and night troughs is normal and healthy. A flattened or inverted pattern is what merits attention.
Which is more accurate, saliva or blood?
They measure different things. Blood reflects total cortisol; saliva reflects biologically active free cortisol. Both have well-established clinical roles, and physicians choose based on the question.
Does a high value mean I have Cushing's syndrome?
Not necessarily. Acute stress, exercise, and even venipuncture itself can transiently elevate cortisol. Diagnosis requires repeat testing, dynamic tests, and often imaging.
What should I do before testing?
Avoid intense exercise, sleep deprivation, and excessive caffeine before testing. Steroid medications can affect results and should be disclosed to your physician.
Do supplements affect cortisol levels?
Adaptogens such as ashwagandha have been studied for effects on stress markers. If you are testing cortisol, disclose all supplements to your clinician.
Are home test kits reliable?
Saliva kits exist for screening and circadian-rhythm assessment. They are not substitutes for diagnostic testing in a clinical setting.
9. Summary
Cortisol reference ranges depend on the time of day and the test method. The pattern of the diurnal rhythm matters more than any single number. If you have persistent symptoms, talk with a clinician rather than self-interpreting. For more on cortisol biology and stress management, see our cortisol pillar guide.