Last Updated on August 14, 2025
When your blood sugar goes higher than expected, it can feel frustrating, but there’s a tool 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
This method estimates how far your blood sugar should drop after taking 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: Calculate how high you are above target
220 – 100 = 120 mg/dL
Step 2: Divide by your correction factor
120 ÷ 50 = 2.4 units
You would then 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 |
Repeat testing with each adjustment.
Why Must You Check Your Basal Insulin First?
A correction factor only works if your basal insulin is accurate:
- Too much basal → CorrF may cause lows
- Too little basal → CorrF may seem ineffective
Test your basal rates:
- For injection users: confirm long-acting insulin keeps glucose steady during fasting
- For pump users: do structured fasting blocks
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:
- To test your CorrF accurately, temporarily switch to manual mode
- Disable auto-corrections
- Follow the same 5-hour testing process
If your AID system isn’t correcting effectively, the CorrF or CarbF may be too weak, the basal rate might be too low, or meal boluses could be underestimated. Keep in mind that AID systems continue micro-dosing to correct high glucose levels, which could mask an inaccurate CorrF unless the user intervenes or carefully observes CGM trends.
In an AID system, a lower CorrF than that determined by the 1800 Rule often improves the glucose level. By using a smaller CorrF number, an AID system provides more insulin when the glucose level is high and lesser amounts as the glucose level comes down. Be cautious, though, if you frequently go low after treating highs, your CorrF number may need to be raised a bit.
Don’t unintentionally stack insulin! This often happens when someone on an AID system forgets to bolus for a meal and then covers the missed meal carbs and their high glucose. Because the AID is already correcting for the missed meal carbs, the glucose goes low from this stacking of insulin!
How Can You Avoid Over-Correcting High Blood Sugar?
Be patient when lowering high glucose. Most rapid-acting insulin uses 70% within the first 3–4 hours but continues to act for up to 5 hours. Know this to avoid insulin stacking.
What If Correction Doses Don’t Work?
Repeated highs may indicate:
- Basal rate too low
- CarbF too high
- Missed or miscounted carbs
- Infusion site issues
- Illness, infection, or stress
Fix the root cause, not just the symptom.
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 a dynamic scale based on your average glucose
- Test your correction factor regularly
- Adjust gradually with guidance
- Confirm your basal settings first
- Integrate CorrF into your complete insulin strategy
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.
Talk to your certified diabetes educator (CDE), endocrinologist, or pump trainer if you’re unsure about your correction factor or how to test your basal insulin settings.