What is a good fasting insulin level?
Updated October 31, 2026 · 15 sources · Written by the AumniVIDA team
UnitsShort answer
Lab normal ranges for fasting insulin are wide, such as 2.6 to 24.9 µIU/mL (16 to 149 pmol/L)16 to 149 pmol/L (2.6 to 24.9 µIU/mL). Studies link values above about 9 to 12.5 µIU/mL (54 to 75 pmol/L)54 to 75 pmol/L (9 to 12.5 µIU/mL) with prediabetes or insulin resistance. No standardized optimal value exists, and results differ between assays.
Reported fasting insulin reference limits and research thresholds
- Below one lab's reference range
- 00 to 2.616
- Within lab range, below research thresholds
- 2.616 to 954
- Thresholds studies have linked to prediabetes or insulin resistance
- 954 to 12.575
- Within lab range, above research thresholds
- 12.575 to 24.9149
- Above one lab's reference range
- 24.9149 to 30180
- 2.6 µIU/mL (multiply by 6.0 for pmol/L)16 pmol/L: Labcorp lower limit
- 9 µIU/mL (multiply by 6.0 for pmol/L)54 pmol/L: Above 9 caught 80% of prediabetes (US clinic)
- 12 µIU/mL (multiply by 6.0 for pmol/L)72 pmol/L: 75th percentile, normal glucose (Spain)
- 12.5 µIU/mL (multiply by 6.0 for pmol/L)75 pmol/L: Hyperinsulinemia cut point, 75 pmol/L (Canada)
- 24.9 µIU/mL (multiply by 6.0 for pmol/L)149 pmol/L: Labcorp upper limit
Key takeaways
What is the normal range for fasting insulin?
It depends on the lab. One large US lab uses 2.6 to 24.9 µIU/mL. Other published ranges run from 5 to 13 µIU/mL to 3 to 28 µIU/mL. Always read your result against the range on your own report.
A reference range shows where most results fall in a lab's reference population. It is not a definition of good health, and for insulin it is wide.
- Labcorp: 2.6 to 24.9 µIU/mL (16 to 149 pmol/L)16 to 149 pmol/L (2.6 to 24.9 µIU/mL) [1].
- Other lab ranges compiled in a 2015 review: 5 to 13 µIU/mL, up to 30 µIU/mL and 3 to 28 µIU/mL (18 to 173 pmol/L)18 to 173 pmol/L (3 to 28 µIU/mL) [6].
The ranges differ partly because labs use different assays that do not agree with each other [7]. That is also why searches for a fasting insulin range in India, Australia or the UK turn up different numbers: each lab sets its own.
What is a good fasting insulin level?
Lower values within the normal range generally go with better insulin sensitivity. Studies have linked values above 9.0 µIU/mL with prediabetes and above about 12 to 12.5 µIU/mL with insulin resistance, but none of these is a validated target.
Research thresholds give more useful anchors than the lab range:
| Threshold | µIU/mL | pmol/L (x 6.0) | What it marked |
|---|---|---|---|
| Johnson 2010 [2] | Above 9.0 | Above 54 | Identified 80% of prediabetes in 965 US patients |
| Ascaso 2003 [8] | 12 | 72 | 75th percentile in Spanish adults with normal glucose |
| Wiebe 2026 [3] | Above 12.5 | Above 75 | Hyperinsulinemia; 36.6% of Canadian adults were above it |
In the Johnson study, people in the lowest fasting insulin quartile averaged 4.9 µIU/mL, and the odds of prediabetes rose with each quartile [2].
Optimal fasting insulin and functional medicine. Many clinicians and wellness programs advertise optimal fasting insulin targets below these thresholds. Lower insulin at a normal glucose generally means less compensation. But the insulin standardization workgroup argued that insulin cannot support clinical cut points until assays are harmonized [4], and no outcome trial has tested a target.
Too low. Very low insulin with normal glucose usually reflects good sensitivity, but in lean adults the lowest HOMA-IR groups also had higher mortality [9]. Low insulin with high glucose is a different matter. See why is my fasting insulin low.
What is a normal fasting insulin in pmol/L?
Multiply µIU/mL by 6.0. A range of 2.6 to 24.9 µIU/mL becomes about 16 to 149 pmol/L, and 9 µIU/mL becomes 54 pmol/L. Converting with 6.945 instead gives pmol/L values about 16% higher.
| µIU/mL (= mU/L) | pmol/L at 6.0 | pmol/L at 6.945 |
|---|---|---|
| 2.6 | 16 | 18 |
| 5 | 30 | 35 |
| 9 | 54 | 63 |
| 12 | 72 | 83 |
| 12.5 | 75 | 87 |
| 24.9 | 149 | 173 |
The correct factor for human insulin is 1 µIU/mL = 6.00 pmol/L; the 6.945 factor is common in calculators and journal style guides and shifts results by about 15% [5]. If your lab reports pmol/L, look for the conversion factor in the report notes before comparing with a µIU/mL threshold.
Does a normal fasting insulin level differ by age, sex or PCOS?
Most labs use one adult range for everyone. Research suggests thresholds may shift with age in women, and insulin resistance is common in PCOS, but no separate standardized ranges by age or sex exist.
- Age and sex. In 2,459 Spanish adults, the HOMA-IR threshold for metabolic risk varied with age in women without diabetes, but not in men [10].
- Ethnicity. HOMA-IR cut points differ widely between populations, from 1.775 in Iran to 3.80 in Mexican Americans [11] [12], which suggests fasting insulin thresholds differ too.
- PCOS. The ADA lists polycystic ovary syndrome as a risk factor for diabetes [13], and metformin lowered HOMA-IR in PCOS trials [14]. People with PCOS often track fasting insulin, but there is no PCOS-specific normal range.
- Pregnancy. Insulin resistance rises normally in pregnancy, and non-pregnant ranges do not apply.
Children have their own reference ranges, which this page does not cover.
Does fasting insulin change from day to day?
Yes. Insulin is released in pulses, and single fasting samples can vary by 25% to 50%. A recent meal, a short night or a different lab can all move the number, so look at trends on the same lab.
Because insulin is pulsatile, one recommendation is to average three samples taken five minutes apart; single samples can vary 25% to 50% [6]. Short sleep lowers insulin sensitivity in randomized trials [15], and different assays read the same sample differently [7].
A practical approach: test under the same conditions each time (same lab, morning, after an overnight fast and a normal night of sleep), and give any lifestyle change at least a few months before retesting. Pair insulin with glucose to calculate HOMA-IR, and track HbA1c and triglycerides alongside it.
More about Fasting insulin
- Fasting insulin: the full guideFasting insulin is the level of insulin in your blood after at least 8 hours without food.
- Fasting insulin test: why it is done and how to prepareA fasting insulin test is a blood test taken after at least 8 hours without food.
- How to calculate HOMA-IR from fasting insulin and glucoseHOMA-IR equals fasting glucose in mg/dL times fasting insulin in µIU/mL, divided by 405.
- How to lower fasting insulinWeight loss lowers fasting insulin the most: in one trial it fell about 15% at 5% weight loss and about 48% at 16%.
- Why is my fasting insulin low?A low fasting insulin with normal glucose usually means your cells are sensitive to insulin, common in lean, active people.
Protocols that act on Fasting insulin
- Low-glycemic dietA low-glycemic diet favors carbohydrate foods that raise blood sugar slowly, rated by the glycemic index (GI): 55 or less is low and 70 or more is high.
- Time-restricted eatingTime-restricted eating means eating all of the day's food and caloric drinks within a consistent daily window, usually 6 to 10 hours, and fasting the rest of the day.
- Ketogenic dietA ketogenic diet keeps carbohydrate under about 20 to 50 g a day so the body burns fat and makes ketones, defined in supervised programs as blood BHB of 0.5 to 3.0 mmol/L.
- Zone 2 cardioZone 2 cardio is steady aerobic exercise held just below the first lactate threshold, where blood lactate stays near 2 mmol/L and you can still talk in full sentences.
Common questions
Is a fasting insulin of 10 good?
Is a fasting insulin of 5 normal?
Yes, 5 µIU/mL (30 pmol/L)30 pmol/L (5 µIU/mL) is within common lab ranges and close to the 4.9 µIU/mL average of the lowest-risk quartile in one study [2].
What fasting insulin is too high?
Is there a fasting insulin levels chart by age?
No standardized chart by age exists for adults. One Spanish study found that HOMA-IR thresholds shift with age in women [10].
Why do different labs give different normal ranges?
Insulin assays are not standardized; in one comparison results differed by a median of 24% between assays [7].
Sources
- 1.Labcorp. Insulin (test 004333). Labcorp test menu, 2026. Link
- 2.Johnson JL, Duick DS, Chui MA, Aldasouqi SA. Identifying prediabetes using fasting insulin levels. Endocrine Practice, 2010. doi:10.4158/EP09031.OR
- 3.Wiebe N, Thompson S, Stenvinkel P, et al. Associations of obesity, systemic inflammation, and hyperinsulinemia with the incidence of non-communicable chronic disease and mortality: A prospective cohort study. Diabetes, Obesity and Metabolism, 2026. doi:10.1111/dom.70568
- 4.Staten MA, Stern MP, Miller WG, et al. Insulin assay standardization: leading to measures of insulin sensitivity and secretion for practical clinical care. Diabetes Care, 2010. doi:10.2337/dc09-1206
- 5.Knopp JL, Holder-Pearson L, Chase JG. Insulin Units and Conversion Factors: A Story of Truth, Boots, and Faster Half-Truths. Journal of Diabetes Science and Technology, 2019. doi:10.1177/1932296818805074
- 6.Crofts C, Zinn C, Wheldon M, Schofield G. Hyperinsulinemia: A unifying theory of chronic disease?. Diabesity, 2015. doi:10.15562/diabesity.2015.19
- 7.Marcovina S, Bowsher RR, Miller WG, et al. Standardization of insulin immunoassays: report of the American Diabetes Association Workgroup. Clinical Chemistry, 2007. doi:10.1373/clinchem.2006.082214
- 8.Ascaso JF, Pardo S, Real JT, et al. Diagnosing insulin resistance by simple quantitative methods in subjects with normal glucose metabolism. Diabetes Care, 2003. doi:10.2337/diacare.26.12.3320
- 9.Kawamoto R, Kikuchi A, Ninomiya D, Kumagi T, Abe M. Excessively Low Insulin Resistance May Increase the Risk of All-Cause Mortality Among Community-Dwelling Individuals Without Diabetes. Cureus, 2025. doi:10.7759/cureus.81773
- 10.Gayoso-Diz P, Otero-González A, Rodriguez-Alvarez MX, et al. Insulin resistance (HOMA-IR) cut-off values and the metabolic syndrome in a general adult population: effect of gender and age: EPIRCE cross-sectional study. BMC Endocrine Disorders, 2013. doi:10.1186/1472-6823-13-47
- 11.Esteghamati A, Ashraf H, Khalilzadeh O, et al. Optimal cut-off of homeostasis model assessment of insulin resistance (HOMA-IR) for the diagnosis of metabolic syndrome: third national surveillance of risk factors of non-communicable diseases in Iran (SuRFNCD-2007). Nutrition & Metabolism, 2010. doi:10.1186/1743-7075-7-26
- 12.Qu HQ, Li Q, Rentfro AR, Fisher-Hoch SP, McCormick JB. The definition of insulin resistance using HOMA-IR for Americans of Mexican descent using machine learning. PLoS One, 2011. doi:10.1371/journal.pone.0021041
- 13.American Diabetes Association Professional Practice Committee. 2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes-2026. Diabetes Care, 2026. doi:10.2337/dc26-S002
- 14.Melin J, Forslund M, Alesi S, et al. The impact of metformin with or without lifestyle modification versus placebo on polycystic ovary syndrome: a systematic review and meta-analysis of randomized controlled trials. European Journal of Endocrinology, 2023. doi:10.1093/ejendo/lvad098
- 15.Sondrup N, Termannsen AD, Eriksen JN, et al. Effects of sleep manipulation on markers of insulin sensitivity: A systematic review and meta-analysis of randomized controlled trials. Sleep Medicine Reviews, 2022. doi:10.1016/j.smrv.2022.101594