Morning cortisol optimal range and reference range

Compiled by Alina Radu, founder of Sera, from the published sources below · Last reviewed November 9, 2026

Sera's bands for Morning cortisol:

Optimal 10 – 18 μg/dL (276 – 497 nmol/L); sufficient 5 – 25 μg/dL (138 – 690 nmol/L); out of range below 5 or above 25 μg/dL.

Evidence grade: Published reference interval. A band that primarily reflects a published adult laboratory or population reference interval. It is not necessarily applicable to every assay or laboratory.

All units

Unit	Optimal	Sufficient	Out of range
μg/dL	10 – 18	5 – 25	below 5 or above 25
nmol/L	276 – 497	138 – 690	below 138 or above 690
ng/mL	100 – 180	50 – 250	below 50 or above 250

What the evidence says

For a sample drawn at about 8 am. The acceptable band is the 5 to 25 μg/dL (138 to 690 nmol/L) morning interval published by MedlinePlus; laboratory intervals vary with the assay (Mayo 7 to 25, Labcorp 6.2 to 19.4). The optimal band starts at 10 μg/dL (300 nmol/L), which the 2024 European and US endocrine society guideline treats as a reasonable sign of normal adrenal function; a morning result below 5 μg/dL makes adrenal insufficiency very likely and needs medical follow-up. The optimal ceiling of 18 μg/dL is a functional target with no published threshold behind it. Oral oestrogen raises total cortisol, and a single sample cannot diagnose Cushing syndrome or adrenal insufficiency.

Sources

Cortisol blood test — MedlinePlus Medical Encyclopedia, US National Library of Medicine, 2025 · Government / public-health guidanceNormal values for a sample taken at 8 in the morning are 5 to 25 mcg/dL (138 to 690 nmol/L). Supports a sufficient band of 5 to 25 μg/dL.
CORT - Overview: Cortisol, Serum — Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceAdults: a.m. 7 to 25 mcg/dL, p.m. 2 to 14 mcg/dL. With symptoms of glucocorticoid deficiency, an 8 a.m. cortisol below 10 mcg/dL calls for further studies. Supports the morning upper edge of 25 and the afternoon band of 2 to 14.
Cortisol — Labcorp, 2026 · Laboratory / reference-interval sourceReference interval: AM 6.2 to 19.4 μg/dL, PM 2.3 to 11.9 μg/dL. A narrower interval than Mayo's on a different assay; shows how far the upper limit moves between laboratories.
European Society of Endocrinology and Endocrine Society Joint Clinical Guideline: Diagnosis and Therapy of Glucocorticoid-induced Adrenal Insufficiency — European Society of Endocrinology and Endocrine Society (Beuschlein F, Else T, Bancos I, et al. — The Journal of Clinical Endocrinology and Metabolism), 2024 · Clinical guidelineA morning cortisol above 300 nmol/L (10 μg/dL) is taken as a reasonable threshold for recovery of adrenal function; below 150 nmol/L (5 μg/dL) adrenal insufficiency is very likely. The guideline is about people coming off glucocorticoids, and it says cortisol should be read as a continuum. Supports an optimal lower edge of 10 μg/dL and a sufficient lower edge of 5.

What Cortisol (Morning) measures

Your cortisol level in the morning, which reflects how the adrenal glands are working.

Morning cortisol reflects adrenal health and your stress response. For accurate results, test between 7 and 9 AM.

Related hormone health markers

See Morning cortisol in the full list of biomarker ranges

This page is a reference for practitioners, not medical advice. Sera's bands are practitioner targets for structured review, not diagnostic thresholds, and Sera does not diagnose or recommend treatment. Read a result alongside the interval printed by the issuing laboratory and the client's history and symptoms. Range set: Sera Production, version 1.0, last reviewed November 9, 2026.