What Are Normal Fasting Blood Glucose Levels?
Normal fasting glucose <100 mg/dL. Prediabetes 100-125. Diabetes ≥126. Enter your reading in mg/dL or mmol/L — instant ADA 2026 classification.
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Reviewed by: Martín Rodríguez (editorial policy ) · Last reviewed:
Result
Classification
Prediabetes – Impaired Fasting Glucose. A sustained value in this range means higher risk of progressing to type 2 diabe
Interpretation
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For guidance only — not medical advice. Consult a licensed healthcare professional.
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A fasting blood glucose test measures blood sugar after at least 8 hours without food. It is the standard first-line screen for prediabetes and type 2 diabetes. This calculator classifies your result using the same thresholds applied by the American Diabetes Association (ADA) Standards of Care 2026 and the World Health Organization (WHO): under 70 mg/dL is hypoglycemia, 70–99 mg/dL is normal, 100–125 mg/dL signals prediabetes (impaired fasting glucose), and 126 mg/dL or above points to the diabetes diagnostic threshold.
Enter your lab result in mg/dL (standard in the US, Latin America) or in mmol/L (standard in Europe, Canada, Australia). The calculator converts automatically and shows which category your value falls into along with a plain-language interpretation of what that means clinically.
Important context: a single elevated reading does not diagnose diabetes on its own. Diagnosis typically requires confirmation on a separate day, or the presence of classic symptoms such as excessive thirst, frequent urination, or unexplained weight loss. This tool helps you understand where your result sits — bring it to your next doctor's appointment to discuss next steps.
When to use this calculator
- Patient who received a lab result of 110 mg/dL and wants to know if this is prediabetes before their next appointment.
- Person with a mmol/L result from a European lab who wants to understand where they stand on the US/international mg/dL scale.
- Type 2 diabetes patient tracking monthly fasting glucose to see if their value has improved and which clinical category they are in.
- Healthcare student or professional verifying ADA 2026 reference range thresholds for fasting plasma glucose.
Fasting Blood Glucose Reference Ranges (ADA 2026 / WHO)
| Category | mg/dL | mmol/L | Recommended Action |
|---|---|---|---|
| Hypoglycemia | < 70 | < 3.9 | Evaluate symptoms; contact doctor |
| Normal | 70–99 | 3.9–5.5 | Retest every 3 years (age > 45) |
| Prediabetes (Impaired Fasting Glucose) | 100–125 | 5.6–6.9 | Lifestyle changes; annual monitoring |
| Diabetes threshold | ≥ 126 | ≥ 7.0 | Confirm on second test; consult doctor |
| Gestational diabetes (IADPSG) | ≥ 92 | ≥ 5.1 | Different criteria — not covered by this calculator |
Fuente: American Diabetes Association — Standards of Care in Diabetes 2026 & WHO — Definition and Diagnosis of Diabetes Mellitus and Intermediate Hyperglycaemia. Values apply to venous plasma, non-pregnant adults. Conversion factor: 1 mmol/L × 18.016 = mg/dL.
How it works
Fasting blood glucose (FBG) — also called fasting plasma glucose (FPG) — is the concentration of glucose in blood after at least 8 hours without caloric intake. It reflects basal glucose metabolism before any meal-induced spike, making it the most widely used and cost-effective screening tool for type 2 diabetes and prediabetes worldwide.
Pregnancy: IADPSG criteria use ≥92 mg/dL as the gestational diabetes threshold — stricter than the general adult criteria. This calculator is not designed for gestational diabetes screening.
Children and adolescents: The ADA recommends screening from age 10 if overweight/obesity is present alongside risk factors.
Medications: Corticosteroids, thiazide diuretics, beta-blockers, and atypical antipsychotics raise fasting glucose. Insulin, oral hypoglycemics, and alcohol suppress it. Always tell your doctor what medications you take.
Home glucometers: Capillary (fingerstick) glucose can differ from venous plasma by 10–15%. Diagnostic thresholds are defined for venous plasma laboratory measurement. Use lab values for this calculator, not glucometer readings, for diagnostic assessment.
This calculator applies the classification algorithm directly:
How It's Calculated
Fasting glucose < 70 mg/dL → Hypoglycemia (evaluate symptoms and causes)
Fasting glucose 70–99 mg/dL → Normal
Fasting glucose 100–125 mg/dL → Prediabetes (Impaired Fasting Glucose)
Fasting glucose ≥ 126 mg/dL (×2) → Diabetes mellitus threshold
Random glucose ≥ 200 mg/dL + symptoms → Diabetes (no repeat needed)If you enter a value in mmol/L, the calculator multiplies by 18.016 to convert to mg/dL before applying the thresholds (standard conversion factor for glucose).
Reference Ranges (ADA 2026 / WHO, venous plasma, non-pregnant adults)
| Category | mg/dL | mmol/L | Recommended action |
|---|---|---|---|
| Hypoglycemia | < 70 | < 3.9 | Evaluate symptoms; contact doctor |
| Normal | 70–99 | 3.9–5.5 | Retest every 3 years (age >45) |
| Prediabetes | 100–125 | 5.6–6.9 | Lifestyle changes; annual monitoring |
| Diabetes threshold | ≥ 126 | ≥ 7.0 | Confirm on second test; consult doctor |
| Pregnancy (IADPSG) | ≥ 92 | ≥ 5.1 | Gestational diabetes (different criteria) |
When These Ranges Do NOT Apply
Disclaimer
This calculator is informational only. It classifies a single glucose value according to standard reference ranges. It is not a diagnostic tool and does not replace professional medical evaluation. If your result is outside the normal range, or if you have symptoms of high or low blood sugar, consult a qualified healthcare provider.
Example: adult with a fasting glucose of 110 mg/dL
Enter: fasting glucose = 110, unit = mg/dL
The calculator converts internally: 110 mg/dL = 6.1 mmol/L
Compares with ADA 2026 / WHO ranges: 100–125 mg/dL falls in prediabetes
Result: Prediabetes – Impaired Fasting Glucose (100–125 mg/dL / 5.6–6.9 mmol/L)
Prediabetes – Impaired Fasting Glucose. A sustained value in this range means higher risk of progressing to type 2 diabetes. Lifestyle intervention (losing 5–7% of body weight, 150 min/week of moderate activity) reduces that risk by 58% according to the Diabetes Prevention Program (NEJM 2002).
Frequently asked questions
What is a normal fasting blood glucose level?
According to the ADA Standards of Care 2026 and WHO criteria, normal fasting plasma glucose is 70–99 mg/dL (3.9–5.5 mmol/L). A value below 70 mg/dL indicates hypoglycemia. Values from 100 to 125 mg/dL indicate prediabetes (impaired fasting glucose), and 126 mg/dL or above, confirmed on a second test, meets the diagnostic threshold for diabetes.
How do I prepare for a fasting blood glucose test?
Fast for at least 8 hours before the test, ideally no more than 12–14 hours. Only plain water is allowed. Avoid food, sugary drinks, coffee, tea, chewing gum, and tobacco. Avoid intense exercise the evening before, as it can lower fasting glucose the following morning. If you take medications, ask your doctor whether to take them before or after the blood draw. Most fasting tests are scheduled for the morning after an overnight fast.
What does a fasting glucose of 110 mg/dL mean?
A value of 110 mg/dL falls in the prediabetes range (100–125 mg/dL). This is above normal but below the diabetes diagnostic threshold. It signals that your body's glucose regulation is becoming less efficient, usually due to developing insulin resistance. Without intervention, 15–30% of people in this range progress to type 2 diabetes within 5 years. However, evidence shows that losing 5–7% of body weight and getting 150 min/week of moderate activity reduces that progression risk by 58% (Diabetes Prevention Program, NEJM 2002). This is a signal to discuss lifestyle modifications with your doctor, not a diagnosis.
What is the difference between fasting glucose, HbA1c, and oral glucose tolerance test (OGTT)?
These are three complementary tests measuring different aspects of glucose metabolism. Fasting glucose (FPG) captures the baseline state after an 8-hour fast — good for initial screening. The Oral Glucose Tolerance Test (OGTT) measures the 2-hour glucose response to a 75 g glucose load and is more sensitive for detecting prediabetes because it catches post-meal dysfunction before fasting levels become abnormal. HbA1c (glycated hemoglobin) reflects the average blood glucose over the past 2–3 months and does not require fasting. Any of the three can be used for diagnosis: HbA1c ≥6.5% means diabetes; 5.7–6.4% means prediabetes.
Can a single elevated fasting glucose reading diagnose diabetes?
In most cases, no. The ADA and WHO require confirmation with a second test on a separate day before establishing a diabetes diagnosis from fasting glucose alone. The only exception is when classic symptoms of hyperglycemia are present simultaneously (excessive thirst, frequent urination, unexplained weight loss, blurred vision) and the random plasma glucose is ≥200 mg/dL. The reasoning is that a single reading can be falsely elevated due to acute stress, illness, certain medications, or recent food intake despite stated fasting. Confirmatory testing reduces misdiagnosis.
Do fasting glucose reference ranges differ by age, sex, or ethnicity?
The diagnostic thresholds are the same for men and women in non-pregnant adults: normal 70–99 mg/dL, prediabetes 100–125 mg/dL, diabetes ≥126 mg/dL. Pregnancy is the major exception: IADPSG criteria for gestational diabetes use a threshold of ≥92 mg/dL, which is stricter. Some research shows modest differences in fasting glucose between ethnic groups at equivalent degrees of insulin resistance, but international guidelines do not currently apply ethnicity-specific thresholds for clinical classification.
What medications can affect fasting blood glucose?
Several commonly prescribed medications alter fasting glucose. Those that raise it include corticosteroids (prednisone, dexamethasone), thiazide diuretics (hydrochlorothiazide), beta-blockers (metoprolol, atenolol), atypical antipsychotics (olanzapine, clozapine), tacrolimus, and some immunosuppressants. Those that lower it include insulin, oral hypoglycemics (metformin, glipizide, empagliflozin), and alcohol (which inhibits hepatic gluconeogenesis during fasting). Always inform your doctor of all medications before interpreting a fasting glucose result. An elevated result while on corticosteroids, for example, may represent drug-induced hyperglycemia rather than diabetes.
How does stress affect fasting blood glucose?
Acute and chronic stress raise blood glucose through cortisol and catecholamines (epinephrine, norepinephrine). These hormones stimulate hepatic glucose production and reduce peripheral uptake — an evolutionary response for energy mobilization under threat. If you had an acutely stressful night before the blood draw (severe anxiety, acute pain, illness), your fasting result may be transiently elevated. Chronic sustained stress can also drive progressive insulin resistance. A single elevated value in a clearly stressful context should be repeated under calmer conditions before drawing clinical conclusions.
Is a home glucometer accurate enough for diagnosing diabetes?
No — home glucometers are not validated for diagnostic purposes. They measure capillary whole blood glucose from a fingerstick, while diagnostic thresholds are established for venous plasma from certified laboratory analysis. Capillary glucometer results can differ from venous plasma by 10–15%, meaning a glucometer might read 90 mg/dL while the lab value is 100 mg/dL. Glucometers are excellent for day-to-day monitoring in diagnosed patients. For initial diagnosis or clinical decision-making, a certified laboratory test is required.
How do I convert between mg/dL and mmol/L?
Divide mg/dL by 18 (more precisely, 18.016) to get mmol/L. Multiply mmol/L by 18 to get mg/dL. Key reference points: 100 mg/dL = 5.6 mmol/L (normal/prediabetes cutoff); 126 mg/dL = 7.0 mmol/L (diabetes diagnostic threshold). This calculator accepts both units and converts automatically before classifying.
What does a fasting glucose below 70 mg/dL mean?
A fasting glucose below 70 mg/dL (3.9 mmol/L) is classified as hypoglycemia. In people without diabetes, fasting hypoglycemia is uncommon and may indicate an insulinoma (insulin-secreting pancreatic tumor), adrenal insufficiency, severe liver disease, or excessive alcohol intake. In people with diabetes taking insulin or sulfonylureas, it is the most immediate treatment risk. Symptoms typically include trembling, sweating, palpitations, and hunger. Values below 54 mg/dL (3.0 mmol/L) are considered clinically significant and require prompt evaluation. If you consistently have low fasting glucose without a diabetes medication explanation, see your doctor.
How often should I test my fasting blood glucose?
Frequency depends on your baseline. Healthy adults with no risk factors and a normal result: every 3 years starting at age 45 (ADA guideline). At any age if you have risk factors such as obesity (BMI ≥25), first-degree relative with diabetes, gestational diabetes history, hypertension, dyslipidemia, or polycystic ovary syndrome. If you are in the prediabetes range, annual or semi-annual retesting is recommended. If you have diagnosed diabetes, your doctor will set the monitoring frequency, which may include weekly glucometer readings plus quarterly HbA1c.
Sources & references
Methodology & trust
Editorial
Calculadora de salud revisada por el equipo editorial de Hacé Cuentas, contrastada con American Diabetes Association — Standards of Care in Diabetes 2026, según nuestra política editorial y metodología.
Updates
Última revisión: June 20, 2026. Los parámetros se verifican periódicamente con las fuentes citadas.
Privacy
Calculations run 100% in your browser. We do not store or transmit your data.
Limitations
Indicative results. For critical decisions, consult a professional.
📌 How to cite this calculator
Rodríguez, M. (2026). What Are Normal Fasting Blood Glucose Levels?. Hacé Cuentas. https://hacecuentas.com/fasting-blood-glucose-levels
Contenido bajo licencia CC-BY 4.0 — reutilizable citando la fuente con enlace a Hacé Cuentas.