Calculate Your Insulin Sensitivity Factor
What Is Insulin Sensitivity Factor (ISF)?
O Insulin Sensitivity Factor (ISF), also known as Insulin Sensitivity Factor, is a value that describes the amount of blood glucose reduction (in mg/dL) that each unit of insulin produces in the body. In other words, it measures the your body's sensitivity to insulin.
For example, if your ISF is 1:50, this means that each 1 unit of insulin lowers your blood glucose by approximately 50 mg/dL. This value is individual and unique to each person, varying with factors such as age, weight, body sensitivity, type of diabetes, type of insulin used, and even factors such as physical activity and stress.
The ISF is essential for calculating the insulin correction dose when blood glucose is above target. Without knowing your ISF, it is very hard to know how much insulin should be given to bring blood glucose back to normal levels.
How Is the ISF Calculated?
The ISF calculation uses the Total Daily Dose (TDD) of insulin and a empirical constant — numbers obtained from observing patients, not from an exact law of physiology.6,7,8
What goes into the TDD (Total Daily Dose)
It is the sum of all the units of insulin injected over 24 hours: the long-acting (basal) e a short/rapid-acting of meals and corrections. In many treatment regimens, basal insulin accounts for about half of the TDD.7
| Long-acting (basal) insulin — e.g., 1 injection of 20 units | 20 units |
| Rapid at breakfast | 6 units |
| Rapid at lunch | 8 units |
| Rapid at dinner | 6 units |
| TDD (daily total) | 40 units |
Note the names: in Brazil, the "rapid" insulin is usually the Regular (human), and the "rapid-acting" are the analogs (lispro, aspart, glulisine).5
Correction with rapid-acting analog (lispro, aspart, glulisine):
ISF = 1800 ÷ TDD (day's long-acting + rapid)
Correction with Regular insulin:
ISF = 1500 ÷ TDD (day's long-acting + rapid)
A 1500 rule was described for Regular insulin, which acts more slowly. For the rapid-acting analogs, constants of 1700 a 1800: a study of well-controlled insulin pump patients arrived at 1700 ÷ TDD,7 and another, with continuous glucose monitoring, showed that the classic formulas are only a starting point and required individual adjustment.8 This calculator uses 1800, the most conservative option (it yields smaller correction doses).
Practical example: the sum of all your insulins for the day comes to 50 units (for example, 24 units of long-acting + 26 units of rapid-acting at meals):
ISF = 1800 ÷ 50 (TDD) = 36 mg/dL
This means that each unit of insulin lowers your blood glucose by approximately 36 mg/dL.
How to Calculate the Correction Dose
Once the ISF is known, it is possible to calculate the insulin correction dose — the estimated amount needed to bring blood glucose back to target when it is above goal.
Correction Dose Formula:
Dose = (Current Glucose − Target Glucose) ÷ ISF
Practical example (using the same data: TDD = 50 units adding long-acting + rapid, correction with rapid-acting, ISF = 36 mg/dL):
- Current Glucose: 280 mg/dL
- Target Glucose: 100 mg/dL
- ISF: 36 mg/dL per unit
Dose = (280 − 100) ÷ 36 = ≈ 5 units
In this example, approximately 5 units of insulin would be needed to correct a blood glucose of 280 mg/dL to the target of 100 mg/dL.
Note: The formula is an estimate. The actual response may vary depending on active insulin (insulin on board), a recent meal, physical activity, and stress. All dose adjustments should be made under the guidance of your doctor.
Type 1 Diabetes (T1D)
A Type 1 Diabetes Mellitus (T1D) is an autoimmune condition in which the pancreas does not produce insulin adequately. People with T1D require exogenous insulin (injected or by pump) to survive. The The ISF is especially important in these patients because they need to make constant insulin adjustments to keep blood glucose under control.5
In T1D, the ISF is usually more sensitive (higher numbers) because the body usually produces no endogenous insulin at all. Patients with T1D often use the carbohydrate counting + correction, where they calculate both the insulin needed to cover the carbohydrates eaten and the insulin to correct blood glucose.
• Total dependence on exogenous insulin
• More sensitive ISF (higher values)
• Need for frequent adjustments
• Regular glucose monitoring is essential
• Higher risk of hypoglycemia
Type 2 Diabetes (T2D)
A Type 2 Diabetes Mellitus (T2D) is the most common type of diabetes, accounting for 90-95% of cases. In this condition, the body still produces insulin, but cannot use it properly (insulin resistance). Many patients with T2D can control the disease with lifestyle changes and medications such as metformin, but some eventually need supplemental insulin.
In T2D, the ISF is usually less sensitive (lower numbers) because the body still has some endogenous insulin production and there is greater insulin resistance. When a patient with T2D starts insulin, it often begins with low doses of basal insulin.
• Endogenous insulin present but insufficient
• Insulin resistance is the central problem
• Less sensitive ISF (lower values)
• Insulin start is usually later
• Higher risk of chronic hyperglycemia
LADA (Latent Autoimmune Diabetes in Adults)
LADA (Latent Autoimmune Diabetes in Adults) is often called "adult T1D" or "slow-onset T1D". It is an autoimmune condition like T1D, but develops more slowly in adults13, often presenting as T2D at first.
In LADA, the immune system gradually attacks the beta cells of the pancreas, resulting in progressive insulin deficiency. Over time, patients with LADA generally need insulin, as in T1D. The ISF in LADA follows intermediate patterns, and may vary depending on the stage of disease progression.
• Autoimmunity like T1D, but slow onset
• Often initially diagnosed as T2D
• Gradual progression to insulin dependence
• ISF intermediate between T1D and T2D
• Requires progressive monitoring and adjustments
Gestational Diabetes
Gestational Diabetes occurs during pregnancy and is one of the most common metabolic changes of gestation (the frequency varies with the diagnostic criterion used). It is caused by insulin resistance induced by pregnancy hormones. Most women can control it with diet and exercise, but some need insulin during pregnancy — and in that case, the targets and adjustments are set by the prenatal care team.3
The ISF in gestational diabetes is typically less sensitive due to pregnancy-induced insulin resistance. Close monitoring is essential, because both hyperglycemia and hypoglycemia can harm the fetus. Gestational diabetes usually resolves after delivery, although the risk of T2D later in life increases.
• Occurs only during pregnancy
• Caused by gestational insulin resistance
• Less sensitive ISF (lower values)
• Requires close prenatal follow-up
• Usually resolves postpartum
Hospital Hyperglycemia
Hospital hyperglycemia is not a type of diabetes: it is elevated blood glucose during a hospital stay, in people with or without a prior diagnosis of diabetes. It is caused by physical stress (infections, surgery, trauma) that increases the production of counter-regulatory hormones and induces hyperglycemia.
In the hospital setting, glycemic control is critical because it contributes to clinical outcomes. The ISF in hospital diabetes is often less sensitive due to the catabolic and inflammatory state. Management is handled by the hospital team, with its own protocols, frequent blood glucose checks, and a preference for regimens with basal insulin + correction rather than a "sliding scale" alone.4
• Acute stress-induced hyperglycemia
• Often transient
• Less sensitive ISF (lower values)
• Managed exclusively by the hospital team
• May reveal previously undiagnosed diabetes (which is why hemoglobin A1c is usually ordered at admission)
Important Risks and Considerations
Although the ISF is a valuable tool, it is important to understand its risks and limitations:
How the Sensitivity Factor Is Adjusted
The calculated ISF is only the starting point. Over time, the doctor adjusts the factor by observing how blood glucose responds to corrections. Understanding the logic helps you talk better during your appointment:
Frequently Asked Questions
Does the TDD include long-acting (basal) insulin?
Yes. The TDD is the sum of all the day's insulins: the long-acting/basal (NPH, glargine, degludec, detemir) plus the short- or rapid-acting insulin for meals and corrections. Using only the rapid makes the factor come out too high and the correction dose wrong.
I use different doses each day. Which TDD should I enter?
Use the average of the last few days (for example, add up the doses from 3 to 7 days and divide by the number of days). If you use an insulin pump, you can find this value in the device's history.
What is the difference between short-acting and rapid-acting insulin?
In Brazil, "short-acting" usually refers to human Regular insulin, which starts working in about 30 minutes. The "rapid-acting" ones are the analogs (lispro, aspart, glulisine), which act sooner and for a shorter time. That is why the rules differ: 1500 for Regular and 1700–1800 for the analogs.
Can I use the result to change my dose today?
No. The result is educational and serves to understand the logic of correction. The actual correction dose depends on the insulin still active, the meal, physical activity, and your doctor's assessment.
Bibliographic References
References reviewed in October 2026. Each number in the text leads to the source; the links open the original article (DOI) and the PubMed record.
- American Diabetes Association Professional Practice Committee. 6. Glycemic Goals, Hypoglycemia, and Hyperglycemic Crises: Standards of Care in Diabetes—2026. Diabetes Care. 2026;49(Suppl 1):S132-S149. DOI: 10.2337/dc26-s006 · PubMed 41358894
- American Diabetes Association Professional Practice Committee. 9. Pharmacologic Approaches to Glycemic Treatment: Standards of Care in Diabetes—2026. Diabetes Care. 2026;49(Suppl 1):S183-S215. DOI: 10.2337/dc26-s009 · PubMed 41358900
- American Diabetes Association Professional Practice Committee. 15. Management of Diabetes in Pregnancy: Standards of Care in Diabetes—2026. Diabetes Care. 2026;49(Suppl 1):S321-S338. DOI: 10.2337/dc26-s015 · PubMed 41358885
- American Diabetes Association Professional Practice Committee. 16. Diabetes Care in the Hospital: Standards of Care in Diabetes—2026. Diabetes Care. 2026;49(Suppl 1):S339-S355. DOI: 10.2337/dc26-s016 · PubMed 41358892
- Silva Júnior WS, Gabbay MAL, Lamounier RN, et al. Insulinoterapia no diabetes mellitus tipo 1 (DM1). Official Guideline of the Brazilian Diabetes Society. 2022. DOI: 10.29327/557753.2022-5
- Walsh J, Roberts R, Bailey T. Guidelines for optimal bolus calculator settings in adults. J Diabetes Sci Technol. 2011;5(1):129-135. DOI: 10.1177/193229681100500118 · PubMed 21303635
- Davidson PC, Hebblewhite HR, Steed RD, Bode BW. Analysis of guidelines for basal-bolus insulin dosing: basal insulin, correction factor, and carbohydrate-to-insulin ratio. Endocr Pract. 2008;14(9):1095-1101. DOI: 10.4158/EP.14.9.1095 · PubMed 19158048
- King AB, Armstrong DU. A prospective evaluation of insulin dosing recommendations in patients with type 1 diabetes at near normal glucose control: bolus dosing. J Diabetes Sci Technol. 2007;1(1):42-46. DOI: 10.1177/193229680700100107 · PubMed 19888378
- Cryer PE. Diverse causes of hypoglycemia-associated autonomic failure in diabetes. N Engl J Med. 2004;350(22):2272-2279. DOI: 10.1056/NEJMra031354 · PubMed 15163777
- International Hypoglycaemia Study Group. Glucose concentrations of less than 3.0 mmol/L (54 mg/dL) should be reported in clinical trials: a joint position statement of the ADA and the EASD. Diabetes Care. 2017;40(1):155-157. DOI: 10.2337/dc16-2215 · PubMed 27872155
- Battelino T, Danne T, Bergenstal RM, et al. Clinical targets for continuous glucose monitoring data interpretation: recommendations from the International Consensus on Time in Range. Diabetes Care. 2019;42(8):1593-1603. DOI: 10.2337/dci19-0028 · PubMed 31177185
- Porcellati F, Lucidi P, Bolli GB, Fanelli CG. Thirty years of research on the dawn phenomenon: lessons to optimize blood glucose control in diabetes. Diabetes Care. 2013;36(12):3860-3862. DOI: 10.2337/dc13-2088 · PubMed 24265365
- Buzzetti R, Tuomi T, Mauricio D, et al. Management of latent autoimmune diabetes in adults: a consensus statement from an international expert panel. Diabetes. 2020;69(10):2037-2047. DOI: 10.2337/dbi20-0017 · PubMed 32847960
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