Insulin Guides & Education
Medically reviewed by Dr. Chhaya Makhija, MD, DipABLM — September 2026
Plain-language explanations of insulin dosing formulas, ratios, insulin types, and the clinical concepts behind every calculator on this site. ADA-referenced. No medical advice.
All Insulin Guides
How to Calculate Insulin Dose
Step-by-step walkthrough of the weight-based and TDD-based formulas used to estimate starting insulin doses.
Insulin-to-Carb Ratio Explained
What the ICR is, how the 500 Rule works, how to use it at meals, and when it needs adjustment.
Insulin Types Explained
Rapid-acting, short-acting, intermediate, long-acting, and ultra-long โ onset, peak, duration, and when each is used.
Insulin Sensitivity Factor Explained
What ISF (correction factor) means, how the 1800 Rule and 1500 Rule work, and how to use ISF for corrections.
How to Read an Insulin Syringe
Understanding U-100 vs U-40 syringes, unit markings, and how to draw the correct dose safely.
Insulin Storage & Expiration
How to store open and unopened insulin, expiration timelines, signs of degraded insulin, and travel tips.
What Is HOMA-IR?
A plain-language explanation of the HOMA-IR index, what it measures, reference ranges, and its limitations.
Insulin Calculator Formulas Reference
Every formula used on this site in one place: TDD, ICR, ISF, HOMA-IR, QUICKI, eAG, pump rates, and more.
Glucose Infusion Rate Explained
The GIR formula, normal neonatal ranges, and the threshold that signals hyperinsulinism.
Basal Rate Testing
How to fast-test each segment, the drift rule, and what invalidates a test.
Insulin Dosing for Dogs & Cats
AAHA starting doses, why cats start on a flat unit, and the U-40 syringe trap.
GMI vs A1c
Why your CGM number and your lab result disagree, and how big a gap is normal.
Vial, Pen & Day-Supply Math
Units per container, 90-day supply maths, and the priming and 28-day rules that break it.
Insulin and Steroids
Why glucocorticoids raise requirements ~50%, the afternoon pattern, and the taper risk.
What Is Insulin on Board?
IOB, duration of action, linear vs exponential decay, and how stacking happens.
Pre-Bolus Timing
How long before a meal to inject, and how to adjust for glucose and meal type.
Glycemic Index & Load Explained
How GI is measured, why GL exists, and the formula and bands for both.
Frequently Asked Questions
Are these guides considered medical advice?
No. All content on this site is strictly for educational purposes. Our guides aim to break down complex dosing formulas and concepts into plain language so you can better understand how insulin works, but they do not replace the personalized guidance of your diabetes care team.
Who writes the educational content?
Ryan Mitchell, our founder, writes and maintains these articles. He works in the healthcare and pharmaceutical industry. Every article cites a published clinical source, and we check the guidance against the ADA Standards of Care. Dr. Chhaya Makhija, a board-certified endocrinologist, reviews the clinical content.
How often are the articles updated?
We review our core educational guides annually or whenever major updates to clinical guidelines (like the ADA Standards of Care in Diabetes) are published. You can always check the "Last reviewed" date at the bottom of the page.
What is the difference between these guides and the calculators?
While our calculators provide mathematical estimates based on your specific inputs, these educational guides explain the underlying clinical theory. They break down the formulas and rules (like the 500 Rule or 1800 Rule) so you understand exactly how those numbers are derived.
Where do the clinical formulas discussed here come from?
All concepts and formulas discussed in our guides are sourced from peer-reviewed medical literature, clinical textbooks, and established organizations such as the American Diabetes Association (ADA) and the Endocrine Society. We publish and cite these sources directly.
Can I share these educational guides with my patients?
Yes. Healthcare professionals, diabetes educators, and clinicians are welcome to share our guides as supplementary reading materials to help patients understand the basics of insulin therapy. However, they must not be used as a substitute for your individualized clinical instructions.
Written by Ryan Mitchell · Last updated: September 2026