T1D Insulin Calculator

Evidence-based dosing for Type 1 Diabetes

⚠️ Medical Disclaimer

This calculator is for educational purposes only and is NOT medical advice. Always follow your endocrinologist's prescribed insulin regimen and dosing instructions. Consult your diabetes care team before making any changes to your treatment plan. Individual insulin needs vary significantly.

Insulin Type

Target BG (mg/dL)

Carb Ratio (ICR)

1:15

1 unit per 15g carbs

Correction Factor (ISF)

1:50

1 unit drops BG by 50 mg/dL

Current Blood Glucose (mg/dL)

Carbs in Meal (grams)

Step-by-Step Calculation

Rounding rules for half-unit dosing:

• • 0.1-0.3 → Round down to whole unit
• • 0.4-0.6 → Round to nearest half unit (0.5)
• • 0.7-0.9 → Round up to whole unit

Recommended Dose

0.0 units

Humalog (Lispro)

⏰ Reminder: Check glucose monitor in 2 hours post-meal

Enter current BG and carb count to calculate dose

Carb Counting Method:

American Diabetes Association. Standards of Care in Diabetes—2025, Section 5 (Nutrition Therapy) & Section 9 (Type 1 Diabetes).

Read ADA Standards 2025 →

500 Rule for Insulin-to-Carb Ratio:

Walsh J, Roberts R. Pumping Insulin: Everything You Need for Success on an Insulin Pump. 6th ed. Torrey Pines Press; 2016. Formula: ICR = 500 ÷ Total Daily Dose.

Validated in pediatrics: Hanas R, et al. "Bolus calculator settings in well-controlled prepubertal children." J Diabetes Sci Technol. 2017;11(3):632-639.

Read Hanas et al. study →

1800 Rule for Insulin Sensitivity Factor:

Walsh J, Roberts R, Bailey TS. "Guidelines for optimal bolus calculator settings in adults." J Diabetes Sci Technol. 2011;5(1):129-135. Formula: ISF = 1800 ÷ Total Daily Dose.

Based on Davidson PC, et al. "Analysis of guidelines for basal-bolus insulin dosing." Endocr Pract. 2008;14(7):933-946.

Read Walsh et al. guidelines →

Correction Dose Formula:

Correction = (Current BG - Target BG) ÷ ISF. Standard algorithm used in insulin pump bolus calculators.

Pediatric Considerations:

DiMeglio LA, et al. "ISPAD Clinical Practice Consensus Guidelines 2018: Glycemic control targets." Pediatr Diabetes. 2018;19(Suppl 27):105-114.

Note: Young children often need more insulin per carb than the 500 Rule suggests, especially at breakfast.

Read ISPAD Guidelines →

⚠️ Important: These calculations provide starting points only. Work with your endocrinologist to adjust ICR and ISF based on actual blood glucose patterns. Values change during honeymoon phase and throughout life with T1D.