Insulin Clinics / Starting and managing

Correction insulin explained

A correction dose is a small extra amount of fast-acting insulin to bring a high reading back toward target. Understanding how it works — and how it goes wrong — prevents many lows.

Last updated: October 2026 · Based on ADA Standards of Care, FDA prescribing information, and NIDDK · General information, not medical advice — see our editorial policy

What a correction dose is

A correction dose (sometimes called a "correction bolus" or "supplemental insulin") is a small extra amount of rapid- or short-acting insulin used to bring a high blood glucose reading back toward your target. It is different from the mealtime dose, which covers the food you are about to eat. Often the two are added together before a meal.

Correction doses are used mostly by people who already take mealtime insulin. People on basal insulin alone usually do not correct highs at all; instead, patterns of high readings lead to an adjustment of the regimen with their team.

The three numbers behind a correction

• Target glucose — the number your team wants you to aim for, for example 120 mg/dL. It may differ by time of day, especially at bedtime.
• Correction factor (also called insulin sensitivity factor, ISF) — roughly how far one unit of insulin lowers your glucose. A factor of 50 means one unit lowers glucose by about 50 mg/dL (about 2.8 mmol/L).
• Insulin on board — how much rapid-acting insulin from earlier doses is still working.

An illustration

Suppose — purely as an example — someone's target is 120 mg/dL, their correction factor is 50, and their reading is 220 mg/dL with no insulin still on board. The reading is 100 mg/dL above target; 100 ÷ 50 = 2, so their plan would call for a 2-unit correction. If they had insulin still active from a dose an hour earlier, the correction would be smaller or none at all.

Clinicians often estimate a starting correction factor with a rule of thumb based on total daily dose and then refine it from real readings. These formulas are tools for your care team, not something to work out on your own.

Stacking: the main danger

Rapid-acting insulin keeps working for about 3–5 hours. If you correct a high, see that glucose is still high an hour later, and correct again, both doses end up working at the same time — and glucose can fall much further than intended. This is called stacking and is a common cause of unexpected lows.

• Pumps and many smart pens or apps track insulin on board and reduce the suggested correction automatically.
• On injections, plans usually say how long to wait before correcting again. Follow that rule even when a high feels stubborn.
• Write down every correction — the time and the amount — so you and your team can see patterns.

Before you correct

• Confirm the reading. Wash your hands and recheck a surprising fingerstick; confirm a CGM reading with a fingerstick if it does not match how you feel.
• Ask why it is high. A missed dose, an underestimated meal, illness, stress, a failed pump site, or damaged insulin all call for different responses.
• Check ketones if glucose is above 250 mg/dL (some plans use 240 mg/dL — follow the level in your plan), especially if you use a pump, and any time you are vomiting or feel unwell — even at lower glucose if you take an SGLT2 inhibitor. High ketones change what to do — see high blood sugar and DKA.
• Be careful at bedtime and before exercise. Many plans use a higher target or smaller corrections at these times to avoid lows.

When a correction does not work

If glucose does not come down as expected after a correction, think about the insulin and the delivery before taking more:

• Is the insulin past its room-temperature limit, or could it have been exposed to heat? See how long insulin can be out of the fridge.
• Did the dose go into a lumpy area (lipohypertrophy)?
• On a pump: is the infusion set kinked, dislodged, or more than its recommended wear time? A failed site can lead to DKA within hours, so many plans say to give the correction by pen or syringe and change the site.
• Are you getting sick?

Glucose that stays high despite corrections, especially with ketones, vomiting, or feeling unwell, needs a call to your care team or urgent care.

Correction factor vs sliding scale

A sliding scale is a fixed table that assigns a dose to each glucose range, without considering food, insulin on board, or your personal sensitivity. Used on its own, it tends to react to highs after they happen rather than preventing them, and is not recommended as the only form of insulin for ongoing care. A personal correction factor, used alongside basal and mealtime insulin, is the more precise approach.

Frequently asked questions