What is a normal TSH level?

Updated October 31, 2026 · 22 sources · Written by the AumniVIDA team

Units

Short answer

Most labs use a normal adult TSH range of about 0.4 to 4.0 or 4.5 mIU/L, but the upper limit rises with age: in NHANES III it was 3.56 mIU/L at age 20 to 29 and 7.49 at 80 and over . Pregnancy needs trimester-specific ranges . Women run slightly higher than men .

TSH upper reference limit by age

US, age 20 to 293.56 mIU/L
NHANES III, 97.5th centile (Surks 2007)
Australia, age 403.75 mIU/L
Western Australia laboratory data (Kahapola-Arachchige 2012)
Scotland, age 31 to 403.98 mIU/L
Tayside TEARS study, 97.5th centile (Vadiveloo 2013)
Australia, age 905 mIU/L
Western Australia laboratory data (Kahapola-Arachchige 2012)
Scotland, over 905.94 mIU/L
Tayside TEARS study, 97.5th centile (Vadiveloo 2013)
US, age 80 and over7.49 mIU/L
NHANES III, 97.5th centile (Surks 2007)

Show the data

TSH upper reference limit by age
Item	Value (mIU/L)	Note
US, age 20 to 29	3.56	NHANES III, 97.5th centile (Surks 2007)
Australia, age 40	3.75	Western Australia laboratory data (Kahapola-Arachchige 2012)
Scotland, age 31 to 40	3.98	Tayside TEARS study, 97.5th centile (Vadiveloo 2013)
Australia, age 90	5	Western Australia laboratory data (Kahapola-Arachchige 2012)
Scotland, over 90	5.94	Tayside TEARS study, 97.5th centile (Vadiveloo 2013)
US, age 80 and over	7.49	NHANES III, 97.5th centile (Surks 2007)

The upper limit of TSH in people without thyroid disease climbs with age in the US, Scotland and Australia, so a value flagged high at 30 can be ordinary at 85.

Key takeaways

1
Large studies treat about 0.45 to 4.49 mIU/L as normal for adults [4][5].
2
The upper limit rises with age, from 3.56 at 20 to 29 to 7.49 mIU/L at 80 and over in NHANES III [1].
3
Women's TSH runs higher than men's, but by no more than 0.1 mIU/L [3].
4
Pregnancy uses trimester-specific ranges; first-trimester upper limits ranged from 2.24 to 6.02 mU/L across cohorts [6].
5
No trial supports a single optimal TSH for everyone [7][8].

What is the normal TSH range for adults?

About 0.4 to 4.0 or 4.5 mIU/L, depending on the lab and assay. Large pooled studies use 0.45 to 4.49 mIU/L, and the ETA treats 4.0 to 10.0 as mildly raised.

Each lab sets its own range from its assay and population, so your report's range is the one to use. The pooled cohort studies behind most risk data define normal as 0.45 to 4.49 mIU/L [5][9] or 0.50 to 4.49 mIU/L [4]. Spencer's third-generation assay found a normal range of 0.39 to 4.6 mU/L [10]. The ETA calls 4.0 to 10.0 mU/L mildly increased [11].

Assays matter near the top of the range. Four common TSH assays agreed well below 2 mU/L but differed by about 1 mU/L at 4.0 [12]. Comparing results from two different labs can therefore mislead.

In the NHANES III reference population, the geometric mean TSH was 1.40 mIU/L [13], and 85% of people without thyroid disease were below 2.5 mIU/L [7]. Units: mIU/L, µIU/mL and mU/L are all the same number.

What is the normal TSH range by age?

The upper limit rises with age. In US adults without thyroid disease it was 3.56 mIU/L at 20 to 29 and 7.49 at 80 and over. Scottish and Australian data show the same rise, though smaller.

Sources: NHANES III [1], TEARS [14], Western Australia [12], Korea [15].

In NHANES III, 10.6% of people aged 20 to 29 without thyroid disease had TSH above 2.5 mIU/L, rising to 40% at 80 and over, and 70% of older people with TSH above 4.5 were inside their age-specific range [1]. A Dutch analysis of 7.6 million results found upper limits rising from age 50 in women and 60 in men [16]. In Western Australia, age-specific limits reclassified only 0.1% to 1.9% of results in most age bands, but more in people aged 85 and over [12].

The Korean data are a reminder that iodine intake shapes the range: TSH ran higher at every age and did not climb with age [15]. Many labs still print one adult range, so an older person's result flagged high may be ordinary for their age [17].

TSH upper reference limits in young and old adults, compiled from four studies (mIU/L) [1]
Study	Younger adults	Oldest adults
US, NHANES III (97.5th centile)	3.56 at 20 to 29	7.49 at 80 and over
Scotland, TEARS (97.5th centile)	3.98 at 31 to 40	5.94 over 90
Western Australia (laboratory data)	3.75 at 40	5.0 at 90
Korea, KNHANES VI (iodine-rich)	6.42 at 19 to 29	6.58 at 70 and over

TSH upper reference limit by age

US, age 20 to 293.56 mIU/L
NHANES III, 97.5th centile (Surks 2007)
Australia, age 403.75 mIU/L
Western Australia laboratory data (Kahapola-Arachchige 2012)
Scotland, age 31 to 403.98 mIU/L
Tayside TEARS study, 97.5th centile (Vadiveloo 2013)
Australia, age 905 mIU/L
Western Australia laboratory data (Kahapola-Arachchige 2012)
Scotland, over 905.94 mIU/L
Tayside TEARS study, 97.5th centile (Vadiveloo 2013)
US, age 80 and over7.49 mIU/L
NHANES III, 97.5th centile (Surks 2007)

Show the data

TSH upper reference limit by age
Item	Value (mIU/L)	Note
US, age 20 to 29	3.56	NHANES III, 97.5th centile (Surks 2007)
Australia, age 40	3.75	Western Australia laboratory data (Kahapola-Arachchige 2012)
Scotland, age 31 to 40	3.98	Tayside TEARS study, 97.5th centile (Vadiveloo 2013)
Australia, age 90	5	Western Australia laboratory data (Kahapola-Arachchige 2012)
Scotland, over 90	5.94	Tayside TEARS study, 97.5th centile (Vadiveloo 2013)
US, age 80 and over	7.49	NHANES III, 97.5th centile (Surks 2007)

The upper limit of TSH in people without thyroid disease climbs with age in the US, Scotland and Australia, so a value flagged high at 30 can be ordinary at 85.

Is the normal TSH range different for women and men?

Slightly. Women have higher TSH than men on average, but the difference is 0.1 mIU/L or less, so labs use the same range. Women are more likely to have thyroid antibodies and thyroid disease.

In 465,593 TSH results, females had significantly higher TSH and free T4 than males, but the gap did not exceed 0.1 mIU/L or 0.1 ng/dL [3]. NHANES III found higher TSH and more thyroid antibodies in women [13], and age-related rises started earlier in women (from 50) than men (from 60) in Dutch data [16].

The bigger difference for women is pregnancy, covered below, and menopause: NICE notes that symptoms of thyroid dysfunction in menopausal women may be mistaken for menopause [18].

What is a normal TSH in pregnancy?

Pregnancy uses its own trimester-specific ranges, ideally from the local population and assay. If none exist, the 2017 ATA guideline allowed an upper limit of about 4.0 mIU/L, or the nonpregnant upper limit minus 0.5 in the first trimester.

The ATA's 2017 guideline recommends population- and trimester-specific TSH and free T4 ranges calculated in women without thyroid disease, with optimal iodine and negative TPO antibodies [2][6]. When those are unavailable, it allowed a fixed TSH upper limit of 4.0 mU/L or subtracting 0.5 mU/L from the nonpregnant upper limit in the first trimester [6].

Real ranges vary widely. Across 22 cohorts with 63,198 women, the TSH upper limit ranged from 2.24 to 6.02 mU/L in the first trimester and 2.67 to 6.15 in the second, and the lower free T4 limit in the first trimester ranged from 0.61 to 1.03 ng/dL (7.8 to 13.2 pmol/L)7.8 to 13.2 pmol/L (0.61 to 1.03 ng/dL) [6]. Shortcut approaches missed many women with a treatment indication compared with trimester-specific ranges [19].

The ATA updated its pregnancy guideline in 2026 using GRADE methods [20]. Thyroid testing and treatment in pregnancy or when trying to conceive should always run through a clinician.

What is the optimal TSH range?

There is no agreed optimal TSH for people who are not on treatment. Some experts favour an upper limit of 2.5 mIU/L; most guidelines keep the wider range. For people on levothyroxine, the ETA suggested aiming for 0.4 to 2.5 mU/L, a target set by a clinician.

Wartofsky and Dickey argued that more than 95% of normal people have TSH below 2.5 mU/L and that values above it often reflect early Hashimoto disease [21]. Surks and colleagues countered that lowering the limit would label 9.7% of the reference population, about 20.6 million Americans, as having thyroid disease without evidence that treatment helps [7].

Treatment trials since then have not found symptom benefits from lowering TSH in subclinical hypothyroidism [8][22]. For people already on levothyroxine, the ETA suggested that most adults aim for a stable TSH in the lower half of the range, 0.4 to 2.5 mU/L [11]; this is a clinician's target, not a reason to change a dose yourself.

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