A correction factor — also called an insulin sensitivity factor or ISF — describes how far one unit of rapid-acting insulin drops your glucose. A correction factor of 50 means one unit lowers you about 50 mg/dL. It is the number behind correction boluses: the math that turns a reading of 250 and a target of 120 into a specific dose. Like the insulin-to-carb ratio, it is personal, time-of-day dependent, and set with your care team.
The concept that keeps corrections safe is insulin on board: rapid-acting insulin works for three to five hours, so a correction taken two hours after a meal bolus lands on top of insulin still actively working. Corrections stacked without accounting for IOB are one of the most common causes of severe lows — pumps and smart pens track IOB automatically for exactly this reason.
Things that make corrections behave unexpectedly:
- High-fat meals still digesting can outlast a correction and push glucose back up.
- Exercise multiplies insulin's effect — the same correction goes further on a walk.
- Sensitivity itself shifts with illness, stress, sleep, and hormones, so the factor is a living number, not a constant.
Descriptively, a correction that keeps overshooting into lows suggests the factor is set too aggressive, and one that barely dents highs suggests too gentle — and recalibrating it is precisely care-team territory.
