Last Updated on August 7, 2025
When your blood sugar goes higher than expected, it can feel frustrating—but there’s a way to bring it down safely and predictably. That tool is called the correction factor (CorrF or CorrF), sometimes incorrectly called an insulin sensitivity factor (ISF). (True insulin sensitivity is measured in terms of weight divided by the total insulin dose. The CorrF or ISF does not do this.) Learning to use your CorrF effectively can help you prevent prolonged highs, improve time in range, and take control of your diabetes management.
In this guide, you’ll learn:
- What a correction factor is and how it works
- How to calculate it using the 1800 Rule (and how it varies)
- How to check the accuracy of your correction factor
- When and how to adjust the CorrF safely
- Real-life examples and advanced tips for pump and AID users
Whether you’re newly diagnosed or fine-tuning your insulin therapy, this article will guide you step by step.
What Is a Correction Factor for Insulin?
A correction factor tells you how much 1 unit of rapid-acting insulin will lower your blood sugar, typically measured in mg/dL per unit. For example, if your correction factor is 1:50, then 1 unit of insulin is expected to lower your blood sugar by 50 mg/dL.
Correction factors are used to bring an elevated blood level back to your target range safely. Once any insulin on board (IOB) that is still active is accurately measured, corrective insulin doses can be given before meals, after meals, or at bedtime, as needed.
An accurate correction factor helps smooth out occasional highs without causing dangerous lows, making it an essential part of individualized insulin therapy.
How Do You Calculate Your CorrF?
Your correction factor number is inversely related to your Total Daily Dose (TDD) of insulin—the total amount of basal and bolus insulin you use in 24 hours—AND your Average Glucose, measured over 14 days or more.
What Is the 1800 Rule?
1800 ÷ TDD = Estimated point drop per 1 unit of insulin
Example:
- TDD = 30 units
- 1800 ÷ 30 = 60
- Your correction factor is 1:60 (1 unit lowers BG by ~60 mg/dL)
Should You Adjust Your Correction Factor Based on Average Glucose?
Yes! Some clinicians adjust the formula based on your 14-day average glucose or A1c:
| Avg Glucose or A1c | (mg/dL) | (mmol/L) |
|---|---|---|
| 100–135 mg/dL (5.1–6.3%) | 2100 ÷ TDD | 117 ÷ TDD |
| 136–155 mg/dL (6.4–7.0%) | 1900–1800 ÷ TDD | 106–100 ÷ TDD |
| 156–198 mg/dL (7.1–8.4%) | 1800–1560 ÷ TDD | 106–87 ÷ TDD |
| 199–241 mg/dL (8.5–10%) | 1560–1325 ÷ TDD | 87–74 ÷ TDD |
| 242–300 mg/dL (10.1–12%) | 1325–1000 ÷ TDD | 74–56 ÷ TDD |
Higher average glucose = stronger correction needed (smaller CorrF)
What Are the Correction Factor Ranges Based on TDD?
| TDD (units/day) | 2000 Rule | 1800 Rule | 1600 Rule | 1400 Rule |
|---|---|---|---|---|
| 20 | 100 | 90 | 80 | 70 |
| 30 | 67 | 60 | 53 | 47 |
| 40 | 50 | 45 | 40 | 35 |
| 50 | 40 | 36 | 32 | 28 |
| 75 | 27 | 24 | 21 | 18 |
| 100 | 20 | 18 | 16 | 14 |
How Do You Use Your Correction Factor?
Scenario Example:
- Your current blood sugar = 220 mg/dL
- Your target blood sugar = 100 mg/dL (before a meal, after a meal, it might be 160 or 180 mg/dL)
- Your correction factor = 1:50
Step 1: 220 – 100 = 120 mg/dL
Step 2: 120 ÷ 50 = 2.4 units
Add 2.4 units of rapid-acting insulin as a correction dose to your meal dose (rounding to 2.5 or 2 units, depending on your delivery method).
Always consult your provider before using a correction dose if you’re unsure or new to insulin therapy.
How Can You Test If Your Correction Factor Works?
- Choose a time when BG > 250 mg/dL
- No food in the past 3 hours
- No insulin bolus in the past 5 hours
- Take a correction bolus based on your CorrF
- Track BG hourly for 5 hours (or review CGM trend)
- BG should land within 20 mg/dL of your target glucose without going low
When Should You Adjust Your Correction Factor?
If you consistently go too low or remain too high, adjust your CorrF by 10%.
| Current CorrF | 10% Stronger (More Insulin) | 10% Weaker (Less Insulin) |
|---|---|---|
| 40 mg/dL | 36 mg/dL | 44 mg/dL |
| 50 mg/dL | 45 mg/dL | 55 mg/dL |
| 60 mg/dL | 54 mg/dL | 66 mg/dL |
Why Must You Check Your Basal Insulin First?
Correction factors only work well if your basal insulin is properly set:
- Too much basal → CorrF may cause lows
- Too little basal → CorrF may seem ineffective
How Does the Correction Factor Differ in AID Systems?
Automated insulin delivery (AID) systems like Tandem Control-IQ, Omnipod 5 SmartAdjust, Medtronic SmartGuard, or Tidepool Loop use CorrF to deliver automated corrections.
To test your CorrF in an AID system:
- Switch temporarily to manual mode
- Disable auto-corrections
- Follow the 5-hour testing process
A lower CorrF than calculated by the 1800 Rule often improves average glucose in AID systems by delivering more correction insulin when needed.
How Can You Avoid Over-Correcting High Blood Sugar?
Most rapid-acting insulin works 70% within the first 3–4 hours but lasts up to 5 hours. Avoid stacking insulin by giving correction doses too soon.
What If Correction Doses Don’t Work?
If correction doses are ineffective, consider:
- Basal rate too low
- CarbF too high
- Missed or miscounted carbs
- Infusion site issues
- Illness, infection, or stress
Key Takeaways on the Correction Factor
- Correction factor for insulin = how much 1 unit of insulin lowers your BG
- Use the 1800 Rule for diabetes or dynamic formulas based on your glucose average
- Check your correction factor regularly and adjust as needed
- Always confirm your basal insulin is accurate first
- Use CorrF in combination with other insulin dosing strategies
Need Support?
Get a copy of Pumping Insulin, 7th Edition to learn more about diabetes management. Also, try out our AID and Pump Settings Tool For Better Glucose Control.
Remember, always talk to your certified diabetes educator (CDE), endocrinologist, or pump trainer if you’re unsure about your correction factor or basal insulin settings.