Insulin Dose Calculator
Calculate insulin bolus doses for meals and corrections. Estimate carb coverage and correction doses using your insulin-to-carb ratio and sensitivity factor.
Medical Disclaimer
This calculator is for educational purposes only. Always follow your healthcare provider's prescribed insulin regimen. Incorrect insulin dosing can cause dangerous hypoglycemia or hyperglycemia. Never adjust your insulin without medical guidance.
Carb Coverage
Correction Dose
Related Calculators
About This Calculator
Calculating insulin doses accurately is one of the most important skills for people with diabetes who take mealtime (bolus) insulin. This calculator helps estimate the insulin needed to cover carbohydrates and correct elevated blood glucose levels, though it should never replace medical advice or prescribed regimens.
How Insulin Dosing Works: Mealtime insulin dosing has two main components:
- Carb Coverage - Insulin to cover the carbohydrates you eat
- Correction Dose - Additional insulin to bring high blood sugar back to target
The Key Personal Factors:
- Insulin-to-Carb Ratio (ICR): How many grams of carbs 1 unit of insulin covers (e.g., 1:10 means 1 unit covers 10g carbs)
- Insulin Sensitivity Factor (ISF): How much 1 unit of insulin lowers your blood glucose (e.g., 1:50 means 1 unit lowers BG by 50 mg/dL)
Important Medical Disclaimer: This calculator is for educational purposes only. Your insulin doses should be determined by your healthcare provider based on your individual needs. Incorrect insulin dosing can cause dangerous hypoglycemia (low blood sugar) or hyperglycemia (high blood sugar). Always follow your prescribed regimen.
For related diabetes tools, see our A1C Calculator and Blood Sugar Converter.
How to Use the Insulin Dose Calculator
- 1Enter your current blood glucose reading from your meter or CGM.
- 2Enter your target blood glucose (typically 80-120 mg/dL or as prescribed).
- 3Select your glucose unit (mg/dL for US, mmol/L for international).
- 4Enter the grams of carbohydrates you plan to eat.
- 5Enter your Insulin-to-Carb Ratio (ICR) as prescribed by your doctor.
- 6Enter your Insulin Sensitivity Factor (ISF) or Correction Factor.
- 7Optionally enter any active insulin on board (IOB) from recent doses.
- 8Review the calculated total bolus dose.
- 9Check the breakdown showing carb coverage and correction components.
- 10Always verify the dose makes sense before administering insulin.
Understanding Insulin-to-Carb Ratio (ICR)
Your ICR tells you how many grams of carbs are covered by 1 unit of insulin.
How ICR Works
Example: ICR of 1:10
- 1 unit of insulin covers 10 grams of carbs
- A 50g carb meal needs: 50 ÷ 10 = 5 units
Example: ICR of 1:15
- 1 unit covers 15 grams of carbs
- A 50g carb meal needs: 50 ÷ 15 = 3.3 units
Common ICR Ranges
| Population | Typical ICR |
|---|---|
| Adults (Type 1) | 1:10 to 1:15 |
| Children | 1:20 to 1:30 |
| Insulin-resistant adults | 1:5 to 1:8 |
| Very insulin-sensitive | 1:20 to 1:25 |
ICR Can Vary By:
Time of day:
- Morning ICR often lower (more insulin needed) due to dawn phenomenon
- Evening ICR may be higher (less insulin needed)
Activity level:
- More activity = may need less insulin
Menstrual cycle:
- Hormones can affect insulin sensitivity
How ICR Is Determined
Your endocrinologist calculates ICR based on:
- Total daily insulin dose
- Weight
- A1C and glucose patterns
- Trial and adjustment over time
The 500 Rule (approximate): ICR ≈ 500 ÷ Total Daily Dose
Example: TDD of 50 units → ICR ≈ 1:10
This is a starting estimate only - always follow your provider's guidance.
Understanding Insulin Sensitivity Factor (ISF)
Your ISF (also called Correction Factor) tells you how much 1 unit of insulin lowers your blood glucose.
How ISF Works
Example: ISF of 50 mg/dL (2.8 mmol/L)
- 1 unit lowers blood glucose by 50 mg/dL
- To drop from 200 to 100 mg/dL: 100 ÷ 50 = 2 units
Example: ISF of 30 mg/dL
- 1 unit lowers blood glucose by 30 mg/dL
- To drop from 200 to 100 mg/dL: 100 ÷ 30 = 3.3 units
Common ISF Ranges
| Population | ISF (mg/dL) | ISF (mmol/L) |
|---|---|---|
| Adults (Type 1) | 30-50 | 1.7-2.8 |
| Children | 50-100 | 2.8-5.6 |
| Insulin-resistant | 15-30 | 0.8-1.7 |
| Very sensitive | 75-100 | 4.2-5.6 |
Factors That Affect ISF
Lower ISF (need more insulin):
- Illness or infection
- Stress
- Less physical activity
- Certain medications (steroids)
Higher ISF (need less insulin):
- Exercise
- Weight loss
- Improved insulin sensitivity
How ISF Is Determined
The 1800 Rule (rapid-acting insulin): ISF ≈ 1800 ÷ Total Daily Dose
Example: TDD of 45 units → ISF ≈ 40 mg/dL
The 1500 Rule (regular insulin): ISF ≈ 1500 ÷ Total Daily Dose
These are starting estimates - actual ISF is refined through glucose monitoring.
Active Insulin (Insulin on Board)
Active insulin, or Insulin on Board (IOB), refers to insulin from previous doses still working in your body.
Why IOB Matters
If you take a correction dose and then eat 2 hours later, that first dose is still active. Taking another full correction could cause hypoglycemia (stacking insulin).
Insulin Action Time
Rapid-acting insulin (Humalog, Novolog, Apidra):
- Onset: 10-15 minutes
- Peak: 1-2 hours
- Duration: 3-5 hours
Approximate IOB over time:
| Hours Since Dose | % Still Active |
|---|---|
| 0 | 100% |
| 1 | 75% |
| 2 | 50% |
| 3 | 25% |
| 4 | 10% |
| 5 | 0% |
Example Calculation
Scenario:
- Took 4 units 2 hours ago
- Current BG: 200 mg/dL
- Target: 100 mg/dL
- ISF: 50 mg/dL
Without IOB consideration: Correction = (200 - 100) ÷ 50 = 2 units
With IOB consideration:
- IOB ≈ 4 × 50% = 2 units still working
- Needed correction = 2 - 2 = 0 units
The active insulin will likely bring you to target!
Pump vs. MDI
Insulin pumps automatically track IOB. If you use multiple daily injections (MDI), you need to estimate IOB manually or use an app/calculator.
Hypoglycemia and Safety Considerations
Understanding when NOT to dose insulin is as important as knowing how to calculate doses.
Signs of Hypoglycemia (Low Blood Sugar)
Mild (BG 55-70 mg/dL / 3.0-3.9 mmol/L):
- Shakiness, trembling
- Sweating
- Hunger
- Fast heartbeat
Moderate (BG 40-55 mg/dL / 2.2-3.0 mmol/L):
- Confusion
- Difficulty speaking
- Blurred vision
- Coordination problems
Severe (BG < 40 mg/dL / < 2.2 mmol/L):
- Loss of consciousness
- Seizures
- Requires assistance
The 15-15 Rule
If blood glucose is below 70 mg/dL:
- Eat 15 grams of fast-acting carbs
- Wait 15 minutes
- Recheck blood glucose
- Repeat if still low
15g fast-acting carbs:
- 4 glucose tablets
- 4 oz fruit juice
- 5-6 hard candies
- 1 tablespoon honey
When NOT to Take Correction Insulin
- Blood glucose below 70 mg/dL - treat the low first
- Uncertain about recent food or insulin
- About to exercise vigorously
- Feeling symptoms of hypoglycemia
- Alcohol consumption (can lower BG unpredictably)
Safety Tips
- Always carry fast-acting glucose
- Wear medical identification
- Teach family/friends about glucagon
- Don't stack insulin doses
- Check BG before driving
- Have a glucagon emergency kit prescribed
Carbohydrate Counting Basics
Accurate carb counting is essential for accurate insulin dosing.
What Are Carbohydrates?
Carbs are the macronutrient that most directly affects blood glucose:
- Sugars: Simple carbs, fast impact
- Starches: Complex carbs, sustained impact
- Fiber: Doesn't raise blood glucose
Reading Nutrition Labels
Key values to find:
- Serving size (measure carefully!)
- Total Carbohydrates (this is what you count)
- Fiber (some subtract for "net carbs")
Example label:
- Serving size: 1 cup
- Total carbs: 45g
- Fiber: 5g
- Net carbs: 40g (if counting net carbs)
Estimating Without Labels
| Food | Serving | Approx Carbs |
|---|---|---|
| Bread | 1 slice | 15g |
| Rice (cooked) | 1/3 cup | 15g |
| Pasta (cooked) | 1/3 cup | 15g |
| Apple (medium) | 1 | 25g |
| Banana (medium) | 1 | 27g |
| Milk | 1 cup | 12g |
| Potato (medium) | 1 | 30g |
Carb Counting Tips
- Use a food scale - Estimating portions leads to errors
- Measure, don't guess - 1 cup of rice isn't "about a cup"
- Read labels every time - Products change
- Use apps - MyFitnessPal, Calorie King have databases
- Keep a food log - Learn how foods affect YOUR glucose
Advanced: Fat and Protein Effects
High-fat and high-protein meals can raise glucose hours later (delayed rise). Some people:
- Take a portion of bolus upfront
- Use extended/dual-wave bolus (pumps)
- Check BG 3-4 hours after eating
Types of Insulin and Timing
Understanding insulin types helps with proper dosing and timing.
Rapid-Acting Insulin
Names: Humalog (lispro), Novolog (aspart), Apidra (glulisine), Fiasp, Lyumjev
| Property | Timing |
|---|---|
| Onset | 10-15 minutes |
| Peak | 1-2 hours |
| Duration | 3-5 hours |
Dosing timing: 15-20 minutes before eating (or at start of meal with ultra-rapid)
Short-Acting Insulin
Names: Regular (Humulin R, Novolin R)
| Property | Timing |
|---|---|
| Onset | 30-60 minutes |
| Peak | 2-4 hours |
| Duration | 5-8 hours |
Dosing timing: 30-45 minutes before eating
Long-Acting Insulin (Basal)
Names: Lantus (glargine), Levemir (detemir), Tresiba (degludec), Basaglar, Toujeo
Purpose: Background insulin, not for meals Duration: 18-42 hours depending on type
Intermediate-Acting Insulin
Names: NPH (Humulin N, Novolin N)
Purpose: Can cover meals but less predictable Duration: 12-16 hours
Meal Timing Guidelines
Rapid-acting:
- Ideal: 15-20 minutes before eating
- If BG low: At start of meal or after
- If BG high: 20-30 minutes before
Why timing matters:
- Insulin and food should "match up"
- Taking insulin too early when BG is normal can cause hypo
- Taking too late can cause post-meal spike
Pre-Bolusing
Taking insulin before eating to allow it to start working:
- Standard: 15-20 minutes before
- High BG: 20-30+ minutes before
- Low BG: At meal or after starting to eat
- Uncertain: During meal
Pro Tips
- 💡Always verify calculated doses make sense before taking insulin.
- 💡Keep a log of your boluses and post-meal glucose to refine your ratios.
- 💡Account for insulin on board to prevent dangerous stacking.
- 💡Your ICR and ISF may vary by time of day - track patterns.
- 💡Weigh or measure foods - eyeballing portions leads to dosing errors.
- 💡If unsure about carbs, estimate conservatively and correct later if needed.
- 💡Check glucose before driving - never drive with low blood sugar.
- 💡Carry fast-acting glucose at all times (tablets, juice, candy).
- 💡Set reminders to check post-meal glucose at 2 hours.
- 💡Review settings with your healthcare provider regularly (every 3-6 months).
- 💡Consider how exercise affects your insulin needs - you may need less.
- 💡When ill, monitor more frequently - insulin needs often increase.
Frequently Asked Questions
Your insulin-to-carb ratio (ICR) is determined by your endocrinologist or diabetes care team based on your total daily insulin dose, weight, and glucose patterns. A common starting estimate is the "500 Rule": ICR = 500 ÷ Total Daily Dose. For example, if you take 50 units total daily, ICR ≈ 1:10. However, this is only a starting point - your actual ICR is refined through monitoring and adjustments. Many people have different ICRs for different times of day.
