CGM Trend Arrow Insulin Correction Calculator
Factor your continuous glucose monitor's trend arrow into a correction dose by projecting where your glucose is heading before you dose.
Why Trend Arrows Change the Dose
A single glucose number is a snapshot; a CGM trend arrow tells you the direction and speed of change. A reading of 200 mg/dL that is rising fast needs more insulin than the same 200 mg/dL that is already falling. Ignoring the arrow is a common cause of both stubborn highs and surprise lows.
This calculator uses the widely taught projected-glucose approach: it estimates where your glucose will be in about 30 minutes, then applies your normal correction formula to that projected value.
The 30-minute change is estimated from the arrow's rate. Rising arrows add insulin; falling arrows subtract it.
Trend Arrow Adjustments Used Here
| Arrow | Rate of change | Projected 30-min change |
|---|---|---|
| ⬆⬆ Rising rapidly | > 3 mg/dL/min | about +75 mg/dL |
| ⬆ Rising | 1–2 mg/dL/min | about +45 mg/dL |
| ➡ Steady | < 1 mg/dL/min | 0 |
| ⬇ Falling | 1–2 mg/dL/min | about −45 mg/dL |
| ⬇⬇ Falling rapidly | > 3 mg/dL/min | about −75 mg/dL |
These are representative educational values. Published expert protocols (Pettus & Edelman; Aleppo) instead add or subtract a fixed number of units based on your sensitivity — your care team can personalize the approach for your CGM and ISF.
How to Use This Calculator
- Read your CGM now. Enter the current glucose your Dexcom or Libre is showing, in mg/dL or mmol/L.
- Set your target. Use the same target your care team gave you for corrections (often 100–120 mg/dL).
- Enter your ISF. Your insulin sensitivity factor is how far 1 unit lowers glucose. Not sure? Estimate it with the 1800 Rule.
- Pick the trend arrow. Match the on-screen arrow to the direction and speed shown on your CGM.
- Add insulin on board. Enter active insulin from recent doses so it is subtracted — this is the step most people skip. Estimate IOB here.
The result projects your glucose about 30 minutes ahead, applies your correction formula, and subtracts IOB — giving an educational estimate to discuss with your care team, not a prescription.
Dexcom vs FreeStyle Libre Trend Arrows
Trend arrows mean slightly different things on each system, so match the speed — not just the picture — when you choose an arrow above.
Dexcom (G6 / G7)
Dexcom shows seven arrow states based on the rate of change over the last 15–30 minutes:
- ⬆⬆ Rising rapidly — more than 3 mg/dL/min (over ~90 mg/dL in 30 min)
- ⬆ Rising — 2–3 mg/dL/min
- ↗ Rising slowly — 1–2 mg/dL/min
- ➡ Steady — under 1 mg/dL/min
- ↘ / ⬇ / ⬇⬇ — the same bands while falling
FreeStyle Libre (Libre 2 / Libre 3)
Libre shows five arrow states:
- ⬆ Rising quickly — faster than 2 mg/dL/min
- ↗ Rising — 1–2 mg/dL/min
- ➡ Changing slowly — under 1 mg/dL/min
- ↘ Falling — 1–2 mg/dL/min
- ⬇ Falling quickly — faster than 2 mg/dL/min
This tool uses a simplified five-arrow model that maps directly to Libre and to the main Dexcom bands. Because each manufacturer sets its own thresholds, treat a "rapid" arrow on either device as the cue to be cautious and recheck.
Frequently Asked Questions
How do CGM trend arrows affect an insulin correction?
A rising arrow means glucose will keep climbing, so a little more insulin is needed; a falling arrow means less. This tool projects your glucose about 30 minutes ahead from the arrow, then applies the standard (BG − target) ÷ ISF correction to that projected value.
Should I give more insulin when the arrow points up?
Generally yes — a rising trend usually warrants a modestly larger correction, while a falling trend warrants a smaller one or none. The exact amount should follow a plan agreed with your care team, and you must still subtract insulin on board.
Do I still subtract insulin on board?
Always. Trend-arrow adjustment does not replace subtracting IOB — it is added on top. Forgetting active insulin from a recent dose is a leading cause of hypoglycemia, especially when the arrow is already turning down.
What if my glucose is falling but still high?
A downward arrow reduces the projected glucose, so the calculated correction shrinks — and may reach zero if the projection lands near target. When falling rapidly, many clinicians advise waiting and rechecking rather than correcting. Follow your care team's guidance.
Do Dexcom and FreeStyle Libre trend arrows mean the same thing?
Not exactly. Dexcom G6/G7 uses seven arrow states and Libre uses five, and each sets its own rate thresholds — a single "rising" arrow on Libre can mean a faster climb than the angled arrow on Dexcom. Match the rate of change rather than the icon shape, and treat any rapid arrow as a signal to be conservative.
How soon after eating can I trust the trend arrow?
Right after a meal a rising arrow mostly reflects food still being absorbed, not a need for more insulin, so correcting on it risks stacking and a later low. Most guidance is to bolus for carbs at the meal and avoid extra arrow-based corrections for about two hours, until any mealtime bolus has had time to work.
Sources
- Pettus J, Edelman SV. "Recommendations for using real-time CGM data for insulin adjustments in type 1 diabetes." J Diabetes Sci Technol. 2017.
- Aleppo G, et al. "A practical approach to using trend arrows on the Dexcom G5 CGM system." J Endocr Soc. 2017.
Last reviewed: June 2025