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MEDICAL WARNING

This calculator is for educational purposes only and should NOT be used for actual insulin dosing without consulting your healthcare provider. Incorrect insulin doses can cause life-threatening hypoglycemia or diabetic ketoacidosis. Always verify calculations with your diabetes care team and follow your prescribed insulin regimen.

Insulin Dosage Calculator

Calculate bolus insulin for meals and blood sugar corrections

Current Blood Glucose
Target Blood Glucose
Typical target: 80-130 mg/dL (4.4-7.2 mmol/L) before meals
Insulin Sensitivity Factor (ISF)
Example: If 1 unit drops BG by 50 mg/dL, enter 50
Carbohydrate Intake
Enter 0 if only correcting blood sugar without eating
Insulin-to-Carb Ratio (I:C)
Example: If your ratio is 1:10, enter 10 (1 unit covers 10g carbs)
Active Insulin (Optional)
Enter any rapid-acting insulin still working from previous doses (usually lasts 3-5 hours)
Quick Reference

Bolus Insulin: Fast-acting insulin taken at meals or to correct high blood sugar.

ISF (Insulin Sensitivity Factor): How much 1 unit lowers your blood glucose (e.g., 50 mg/dL).

I:C Ratio: How many carbs 1 unit covers (e.g., 1:10 means 1 unit for 10g carbs).

IOB (Insulin on Board): Active insulin from previous doses still working.

Typical Ratios

Insulin Sensitivity (ISF):

  • Type 1 Adults: 30-50 mg/dL
  • Type 2 on insulin: 25-40 mg/dL
  • Very sensitive: 60-100 mg/dL
  • Insulin resistant: 15-25 mg/dL

Carb Ratio (I:C):

  • Adults: 1:8 to 1:15
  • Children: 1:15 to 1:30
  • Insulin resistant: 1:5 to 1:8
  • Very sensitive: 1:20 to 1:30
When to Seek Help

Call 911 if:

  • Blood sugar <54 mg/dL (3.0 mmol/L)
  • Confusion, seizures, unconsciousness
  • Blood sugar >400 mg/dL with ketones
  • Persistent vomiting
  • Difficulty breathing
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Insulin Therapy:

Understanding Insulin Dosing

The Insulin Dosage Formula

Total bolus insulin consists of two components:

1. Food Bolus:

Carbs (g) ÷ Carb Ratio = Units

2. Correction Dose:

(Current BG - Target BG) ÷ ISF = Units

3. Subtract Active Insulin:

Total = Food Bolus + Correction - IOB

Example: 60g carbs, ratio 1:10, BG 200, target 100, ISF 50:
Food: 60÷10 = 6 units
Correction: (200-100)÷50 = 2 units
Total: 6 + 2 = 8 units

Types of Insulin

Rapid-Acting (Bolus):

  • Humalog, Novolog, Apidra: Onset 10-15 min, peak 1-2 hrs, duration 3-5 hrs
  • Fiasp: Ultra-rapid, onset 5-10 min
  • Use: Mealtime coverage and corrections

Long-Acting (Basal):

  • Lantus, Basaglar: Duration 20-24 hrs
  • Levemir: Duration 12-24 hrs
  • Tresiba: Duration 42+ hrs
  • Use: Background insulin, not for corrections

Determining Your Insulin Ratios

The 500 Rule (Carb Ratio)

Carb Ratio = 500 ÷ Total Daily Insulin

Example: If you take 50 units of insulin per day total (basal + bolus):

500 ÷ 50 = 10
Your ratio is 1:10 (1 unit covers 10g carbs)

The 1800 Rule (ISF)

ISF = 1800 ÷ Total Daily Insulin

Example: If you take 50 units of insulin per day:

1800 ÷ 50 = 36
1 unit drops BG by 36 mg/dL

Note: Use 1500 rule for regular insulin

Insulin Timing & Absorption

Insulin Type Brand Names Onset Peak Duration When to Inject
Ultra-Rapid Fiasp, Lyumjev 5-10 min 30-90 min 3-4 hours At start of meal or within 20 min after
Rapid-Acting Humalog, Novolog, Apidra 10-15 min 1-2 hours 3-5 hours 15 min before meal
Short-Acting Regular (R), Humulin R 30 min 2-3 hours 5-8 hours 30 min before meal
Intermediate NPH (N), Humulin N 1-2 hours 4-8 hours 12-16 hours Twice daily for basal
Long-Acting Lantus, Basaglar, Levemir 1-2 hours No peak 20-24 hours Once daily, same time
Ultra-Long Tresiba, Toujeo 1-2 hours No peak 42+ hours Once daily, flexible timing

Factors Affecting Insulin Needs

Increase Insulin Needs

  • Illness/infection: Stress hormones raise BG
  • Stress/anxiety: Cortisol increases glucose
  • High-fat meals: Delayed glucose rise
  • Steroids: Prednisone, cortisone
  • Menstruation: Hormonal changes (premenstrual)
  • Weight gain: Increases insulin resistance
  • Sedentary lifestyle: Less insulin sensitivity

Decrease Insulin Needs

  • Exercise: Muscles use glucose, increases sensitivity
  • Alcohol: Blocks liver glucose release
  • Weight loss: Improves insulin sensitivity
  • Hot weather: Faster insulin absorption
  • Injection site rotation: Fresh sites absorb better
  • Hormonal changes: First trimester pregnancy

Variable Effects

  • Dawn phenomenon: Higher BG 4-8am (more insulin needed)
  • Somogyi effect: Rebound high after nighttime low
  • Gastroparesis: Delayed stomach emptying
  • Celiac disease: Affects carb absorption
  • Kidney disease: Insulin cleared more slowly

Insulin Stacking & Insulin on Board (IOB)

Avoid Insulin Stacking

Insulin stacking occurs when you take correction doses too frequently, before previous insulin has finished working. This can cause dangerous hypoglycemia.

How to Calculate IOB:

  • Rapid-acting insulin lasts 3-5 hours
  • Use "linear decay" method: subtract 20% per hour
  • Example: Took 5 units 2 hours ago → 3 units still active
  • Many insulin pumps/apps calculate this automatically

Safe Correction Timing:

  • Wait at least 2-3 hours between corrections
  • Check BG trend, not just single reading
  • Account for recent meals (glucose may still be rising)
  • Consider recent exercise (delayed glucose drop)

Carbohydrate Counting Guide

Reading Food Labels

Total Carbohydrates: This is the number you need for insulin dosing.

  • Serving size: Check if you're eating more/less than listed
  • Total carbs: Includes sugars, fiber, starch
  • Fiber: If >5g, subtract half from total (net carbs)
  • Sugar alcohols: Subtract half if listed separately

Example: Label shows 30g total carbs, 8g fiber
Net carbs = 30 - (8÷2) = 26g

Common Food Portions

  • Bread: 1 slice = 15g
  • Rice/pasta (cooked): 1/3 cup = 15g
  • Potato (baked): 1 small (3 oz) = 15g
  • Apple: 1 small = 15g
  • Banana: 1/2 medium = 15g
  • Milk: 1 cup = 12g
  • Yogurt: 3/4 cup plain = 12g
  • Beans (cooked): 1/2 cup = 15g

Tip: Use the "15g = 1 carb choice" method to simplify counting

Trusted Diabetes Resources

American Diabetes Association (ADA)

The leading organization providing diabetes research, information, and advocacy.

CDC Diabetes Resources

Centers for Disease Control and Prevention diabetes prevention and management information.

JDRF

Juvenile Diabetes Research Foundation - Type 1 diabetes research and advocacy.

Visit JDRF

Diabetes.co.uk

Comprehensive diabetes community with tools, forums, and education.

Visit Diabetes.co.uk

Mayo Clinic

Evidence-based diabetes information from leading medical experts.

Visit Mayo Clinic

Hypoglycemia (Low Blood Sugar) Management

Mild (54-70 mg/dL)

Symptoms: Shakiness, sweating, hunger, rapid heartbeat

Treatment (Rule of 15):

  • 15g fast-acting carbs (4 glucose tabs, 4 oz juice, 1 tbsp honey)
  • Wait 15 minutes
  • Recheck BG, repeat if still low
  • Eat a snack with protein once normalized

Moderate (<54 mg/dL)

Symptoms: Confusion, difficulty concentrating, irritability, blurred vision

Treatment:

  • 20-30g fast-acting carbs immediately
  • Have someone stay with you
  • Check BG every 15 minutes
  • Do not drive or operate machinery
  • Call for help if not improving

Severe (Unconscious)

Symptoms: Seizures, loss of consciousness, unable to swallow

DO NOT give food/drink to unconscious person

Treatment:

  • Call 911 immediately
  • Give glucagon injection if available
  • Turn person on side (recovery position)
  • Stay until help arrives

Insulin Storage & Handling

Storage Guidelines

  • Unopened vials/pens: Refrigerate at 36-46°F (2-8°C), use before expiration
  • In-use vials/pens: Room temperature OK for 28 days (varies by type—check package insert)
  • Never freeze: Frozen insulin loses potency permanently
  • Avoid extreme heat: Don't leave in hot car (>86°F/30°C)
  • Protect from light: Keep in original packaging or case
  • Traveling: Use insulated case; can go through airport security

Injection Technique

  • Rotation: Rotate injection sites to prevent lipodystrophy (lumps/indentations)
  • Best sites: Abdomen (fastest), arms, thighs, buttocks
  • Pinch technique: For lean individuals, pinch skin to avoid IM injection
  • Needle length: 4mm-8mm; shorter needles reduce pain
  • Angle: 90° for most; 45° if very thin
  • Wait after injection: Count to 10 before removing pen needle
  • Alcohol swab: Let dry completely before injecting

Frequently Asked Questions

Never take a dose that doesn't feel right. If the calculated dose seems wrong, double-check your inputs (current BG, carbs, ratios). Your carb ratio and ISF may need adjustment—these aren't fixed and can change over time with weight changes, activity level, or insulin resistance. Contact your healthcare provider if you consistently need to adjust from calculated doses. They can help you fine-tune your ratios. When in doubt, it's safer to take less insulin initially, check your BG in 2 hours, and take a small correction if needed.

High-fat and high-protein meals can cause delayed and prolonged blood sugar rises, sometimes 3-5 hours after eating. For pizza, pasta with cream sauce, or fatty meats, consider: (1) Split the dose: Take 50-60% of insulin upfront, the rest 1-2 hours later, or (2) Use an extended bolus if you have an insulin pump (deliver insulin over 2-3 hours), or (3) Add 10-30% extra insulin for high-fat meals and check BG more frequently. Track your response to specific meals and adjust your strategy based on patterns. Fat doesn't directly raise BG but slows carb absorption and can cause insulin resistance.

Alcohol is tricky for diabetes management. It has calories but blocks the liver from releasing glucose, which can cause delayed hypoglycemia (lows) hours after drinking, especially overnight. Guidelines: (1) Never drink on an empty stomach—always have food, (2) Count carbs in mixed drinks/beer (light beer ~5g, regular beer ~13g, sweet wine ~5g, hard liquor 0g), (3) Reduce insulin doses when drinking—many people reduce mealtime insulin by 20-50%, (4) Check BG before bed (aim for >140 mg/dL) and set an alarm to check overnight, (5) Wear medical ID and drink with someone who knows you have diabetes. Consider eating extra carbs before bed without insulin.

Exercise lowers blood sugar both during and up to 24 hours after activity. Strategies depend on timing: Before exercise: If BG <100, eat 15-30g carbs without insulin. If BG 100-180, reduce pre-exercise bolus by 25-50%. During exercise: Check BG every 30 min for long workouts; consume 15-30g carbs per hour for moderate activity. After exercise: Risk of delayed lows for 4-24 hours—reduce basal insulin by 10-20% if you have a pump, or reduce next mealtime bolus by 10-30%. Anaerobic exercise (weightlifting, sprints) can actually raise BG due to adrenaline. Keep fast-acting carbs and glucagon handy during all exercise. Develop personalized strategies through trial and CGM/BG monitoring.

There's no universal "maximum" dose—it depends entirely on your individual insulin sensitivity and needs. Some people with severe insulin resistance may require 30-50+ units per meal, while others need only 2-5 units. However, sudden large increases are concerning. If you're typically taking 5 units and the calculator suggests 25 units, something is wrong (incorrect carb count, wrong ratio entered, etc.). General safety rules: (1) Never increase doses by more than 10-20% without medical guidance, (2) If a dose >20 units seems needed, double-check all calculations, (3) For very large meals (>100g carbs), consider splitting into two smaller meals with separate doses, (4) Always re-check BG 2 hours post-meal to verify dose was appropriate. When in doubt, start conservatively and correct later.

Officially, manufacturers and medical organizations recommend single use only for safety and sterility. However, many people reuse their own syringes/needles for cost reasons. If you choose to reuse: (1) Only reuse your own needles, never share, (2) Recap carefully after each use to maintain sterility, (3) Discard if needle becomes dull, bent, or contaminated, (4) Don't reuse more than 3-4 times maximum, (5) Higher infection risk if you have poor circulation, immune issues, or don't maintain hygiene. Reused needles are more painful (they dull quickly) and can cause lipodystrophy. Check if your insurance covers supplies or look into patient assistance programs—proper supplies are worth the investment for health and comfort.
CRITICAL MEDICAL DISCLAIMER

This calculator is for EDUCATIONAL PURPOSES ONLY and must not be used to determine actual insulin doses without supervision from your healthcare provider.

Insulin dosing is highly individualized and must be determined by your doctor or certified diabetes educator. Incorrect insulin doses can cause:

  • Severe hypoglycemia: Can lead to seizures, loss of consciousness, brain damage, or death
  • Diabetic ketoacidosis (DKA): Life-threatening condition from too little insulin
  • Long-term complications: Poor glucose control damages organs over time

Always: Verify calculations, work with your healthcare team to determine your personal insulin ratios, never make major dose adjustments without medical guidance, check blood glucose 2 hours after meals, and seek immediate medical attention for severe high or low blood sugar.