Insulin Stacking Risk Estimator
Estimate how much insulin is still active from your last dose, and assess the risk of stacking a new dose on top of it.
Educational estimator only - not medical advice.
Rapid-acting: NovoLog, Humalog, Apidra, Fiasp * Regular: Humulin R, Novolin R
Range: 0.5-100 units
Range: 0-12 hours (rapid-acting duration: 4h)
Range: 0-100 units
Fill in your last dose details above to assess your insulin stacking risk.
This calculator uses a linear decay model to estimate Insulin on Board (IOB) - the amount of insulin still actively lowering blood glucose from your previous dose:
Where duration is 4 hours for rapid-acting insulin and 6 hours for regular insulin. The model assumes linear decay - in reality, insulin action is more complex (biexponential), but this approximation is widely used in clinical decision support.
The total effective dose = IOB + planned new dose. Stacking risk is assessed based on the combined insulin load relative to typical correction thresholds.
Note: Advanced insulin pumps with closed-loop systems use more sophisticated IOB models. This calculator is for educational awareness only.
Insulin stacking occurs when you administer a new insulin dose before a previous dose has finished working. Since insulin's peak action is delayed (typically 60-90 minutes for rapid-acting), people sometimes assume a dose "isn't working" and take more - leading to a dangerous overlap of effects.
Why it's dangerous: Both doses reach their peak effect, causing blood glucose to drop far lower than intended - potentially causing severe hypoglycemia (low blood sugar), which can cause confusion, loss of consciousness, seizures, or in extreme cases, death.
Common triggers: Impatience after a mealtime bolus, correcting a high BG too soon after a previous correction, or miscounting doses. Always account for active insulin before taking any new dose.
Prevention: Track your doses with time stamps. Use a CGM if available to see glucose trends in real time. Wait for your insulin type's full duration before concluding it isn't working.
Understand how insulin action works - onset, peak, and duration - and how to safely manage mealtime and correction doses without stacking. Covered in depth in FOD Mature.
FOD Mature - Ch. 11: InsulinThis calculator is for educational awareness only. Insulin dosing decisions - including whether to take a new dose when prior insulin is still active - must be made in consultation with your diabetes care team. Insulin stacking can cause severe hypoglycemia, which is a medical emergency. Never rely solely on this tool when making an insulin dosing decision. Always follow the guidance provided by your endocrinologist, diabetes educator, or prescribing clinician.