Managing insulin effectively requires understanding several key concepts and calculations. This page explains the most important tools for insulin dosing — written for patients on multiple daily injections (MDI) or insulin pumps. Always use these tools with guidance from your care team; your specific numbers are personalized by your endocrinologist.
⚠️ Important: The calculators on this page are for educational purposes. Your actual insulin-to-carb ratio, correction factor, and target glucose are set by your endocrinologist based on your individual needs. Never change your insulin doses without consulting your care team.
Basal vs. Bolus Insulin — The Foundation
A healthy pancreas delivers insulin in two patterns. Modern insulin therapy tries to replicate this:
| Basal Insulin | Bolus Insulin | |
|---|---|---|
| What it does | Provides steady background insulin 24/7 to manage glucose between meals and overnight | Covers carbohydrates eaten at meals and corrects high blood sugar |
| When given | Once or twice daily (MDI) or continuously (pump) | At each meal or snack, and for corrections |
| Examples (MDI) | Glargine (Lantus, Basaglar, Toujeo), Detemir (Levemir), Degludec (Tresiba) | Lispro (Humalog), Aspart (NovoLog), Glulisine (Apidra), faster Aspart (Fiasp) |
| Examples (pump) | Basal rate programmed per hour | Meal bolus + correction bolus |
| Goal | Keep fasting and between-meal glucose stable | Prevent post-meal spikes and correct highs |
📐 Basal/Bolus Split: For most patients on intensive insulin therapy, basal insulin makes up roughly 40–50% of total daily insulin (TDI), with bolus insulin covering the remaining 50–60%. If your basal dose is much higher than 50%, it may be doing work that should be managed through other means.
Insulin-to-Carb Ratio (ICR)
The insulin-to-carb ratio tells you how many grams of carbohydrates one unit of rapid-acting insulin will cover. It is used to calculate your meal bolus.
Example: If your ICR is 1:15 (1 unit per 15g carbs), and your meal has 60g of carbs:
60 ÷ 15 = 4 units of meal bolus insulin needed.
ICR varies person to person and can differ by time of day (breakfast often requires more insulin per carb due to the dawn phenomenon). Your endocrinologist sets your ICR based on your patterns.
The "500 Rule" (starting estimate): Divide 500 by your total daily insulin dose (TDI) to estimate your ICR. For example, if you take 50 units/day total: 500 ÷ 50 = ICR of 1:10 (1 unit per 10g carbs). This is a starting point — always adjust based on your actual glucose responses.
🧮 Meal Bolus Calculator
Correction Factor (Insulin Sensitivity Factor)
The correction factor (CF) — also called the insulin sensitivity factor (ISF) — tells you how much one unit of rapid-acting insulin will lower your blood sugar. It is used to calculate a correction bolus when your glucose is above your target.
Example: If your CF is 50 mg/dL per unit, your target is 120 mg/dL, and your current glucose is 270 mg/dL:
(270 − 120) ÷ 50 = 3 units correction bolus needed.
The "1800 Rule" (starting estimate): Divide 1800 by your total daily insulin dose (TDI) to estimate your CF. For example, if you take 50 units/day: 1800 ÷ 50 = CF of 36 mg/dL per unit (meaning 1 unit drops glucose ~36 mg/dL).
🎯 Correction Bolus Calculator
Using Both Together — The Full Bolus Calculation
When eating a meal with an elevated blood sugar, your total bolus = meal bolus + correction bolus (minus any active insulin on board):
🍽️ Total Bolus Calculator (Meal + Correction)
Sick Day Rules
Illness — especially infections, fever, nausea, and vomiting — dramatically affects blood sugar and insulin needs. Having a sick day plan in place before you get sick is essential.
✅ Always Do
- Never stop your basal insulin — even if you can't eat, your body still needs background insulin
- Check blood sugar every 2–4 hours
- Check urine or blood ketones if glucose is above 250 mg/dL (especially Type 1)
- Stay hydrated — sip fluids continuously
- Contact your care team if you can't keep fluids down
⚠️ Watch For
- Blood sugar consistently above 300 mg/dL
- Moderate or large ketones (Type 1 diabetes)
- Vomiting more than 1–2 times (can't keep fluids down)
- Rapid breathing, fruity breath, abdominal pain (possible DKA)
- Confusion or extreme fatigue
🍵 What to Eat/Drink
- Clear fluids: water, broth, herbal tea, Pedialyte
- If glucose is low: regular soda, juice, sports drinks
- If glucose is high: sugar-free fluids only
- Bland foods if tolerated: crackers, toast, rice, applesauce
📞 Call Us or Go to ER If
- Blood sugar above 300 mg/dL that won't come down
- Large ketones present
- Can't keep any fluids down for more than 4 hours
- Signs of DKA: rapid breathing, vomiting, confusion, fruity breath
- Any doubt about safety
💊 Metformin & SGLT2 Inhibitors on Sick Days: Hold metformin if you're severely dehydrated or unable to keep fluids down (kidney risk). Hold SGLT2 inhibitors (Jardiance, Farxiga) during illness — they increase ketone production and risk of euglycemic DKA even at normal blood sugars. Restart when you are eating and drinking normally. Call our office if you're unsure.
Hypoglycemia: The 15-15 Rule
Hypoglycemia (low blood sugar) is defined as glucose below 70 mg/dL. Severe hypoglycemia (below 54 mg/dL or with symptoms of confusion, seizure, or loss of consciousness) requires immediate action.
🍊 The 15-15 Rule
- Treat immediately with 15 grams of fast-acting carbohydrates
- Wait 15 minutes — do not eat more yet
- Recheck your blood sugar
- If still below 70 mg/dL, repeat — 15g more, wait 15 min, recheck
- Once glucose is above 70 mg/dL, eat a small snack with protein and carbs if your next meal is more than an hour away (e.g., crackers and peanut butter)
What Counts as 15g of Fast-Acting Carbs?
| Treatment Option | Amount = 15g carbs | Notes |
|---|---|---|
| Glucose tablets | 3–4 tablets | ✅ Best option — precise, portable, fast |
| Glucose gel (e.g., GlucoBurst) | 1 tube | ✅ Good for people who struggle swallowing |
| Regular (not diet) soda | 4 oz (½ cup) | ✅ Works well — avoid diet versions |
| Orange juice or apple juice | 4 oz (½ cup) | ✅ Fast — avoid if over-treating |
| Honey or corn syrup | 1 tablespoon | ✅ Good if swallowing is difficult |
| Candy (Skittles, Smarties, Lifesavers) | Check label for 15g | Works, but use only if nothing else available |
| Chocolate, peanut butter, cheese | ❌ Not effective | Fat slows glucose absorption — too slow for acute lows |
| Diet soda | ❌ Does not work | Contains no sugar |
Severe Hypoglycemia — Glucagon
If someone is unconscious, having a seizure, or cannot swallow safely, do NOT give food or juice. Use emergency glucagon:
- Baqsimi — nasal glucagon powder, no injection needed, works in minutes
- Gvoke — auto-injector glucagon pen
- Zegalogue — dasiglucagon auto-injector
- Call 911 if glucagon is not available or the person does not respond within 15 minutes
All patients on insulin — especially those with Type 1 diabetes or frequent lows — should have a glucagon kit at home and ensure family members know how to use it.
Quick Reference Summary
- Basal insulin: Background — taken once/twice daily; don't skip, even when sick
- Meal bolus: Carbs ÷ ICR = units to take before eating
- Correction bolus: (Current BG − Target BG) ÷ Correction Factor = units to give
- Don't stack corrections: Factor in insulin on board before correcting
- Sick days: Never stop basal insulin; check ketones if BG > 250; hold metformin and SGLT2i if vomiting or severely ill
- Lows: 15g fast carbs → wait 15 min → recheck → repeat if still below 70
- Severe low: Glucagon (Baqsimi, Gvoke) + call 911 if no response
Our Team Manages Diabetes Technology
Our providers are experienced with insulin pumps, CGMs, and advanced diabetes technology. Book with any member of our team:
Book an Appointment → or call 832-968-7003