Free tool

Correction dose calculator

For rapid-acting insulin (like NovoRapid, Humalog or Apidra) only. It works from numbers only you and your care team know — your own correction factor and target — and refuses a number when insulin may still be active.

Step 1 — Work out your numbers

If your doctor has already given you a correction factor, skip to step 2 and enter it there. Otherwise, this gives you a starting estimate from your total daily insulin dose — a well-known method, not a substitute for numbers confirmed against your own glucose readings.

Total daily insulin doseall your insulin for one full day added together — basal/long-acting plus every rapid-acting dose

units/day

Enter your total daily dose to see an estimate.

The carb ratio is shown for your own reference only — this tool does not use it to size a dose for a meal or snack. Carb-to-insulin dosing should come from your care team.

Already know your correction factor? You can skip straight to step 2 and type it in there.

This is a starting estimate, not a prescription

These formulas (the “1800 rule” and “500 rule”) are a common way to estimate a starting point, but they are averages. The research behind them found the traditional constant can under-estimate for many people — real studies have suggested numbers closer to 1960 than 1800. Confirm your own numbers with your care team using your actual glucose readings.

Step 2 — Calculate your correction dose

Current blood glucose

mg/dL

Your target blood glucosethe number your care team gave you — not a guess

mg/dL

Correction factorfrom step 1, or your own if your doctor has given you one

mg/dL/unit

Hours since your last rapid-acting insulin dosethe fast-acting, mealtime kind — not your long-acting insulin or tablets

hours

Enter your numbers above to calculate.

How the numbers work

A correction dose brings a high reading back toward your target: (current glucose − target) ÷ correction factor. Your correction factor — how many mg/dL one unit of rapid-acting insulin lowers your glucose — can be estimated from your total daily dose, but is best set and adjusted with your care team from your own readings.

This is a calculation, not an instruction

This tool works only from the numbers you type in — it doesn’t know your medical history, your other medicines, or what your own doctor has told you. If anything here disagrees with your care team’s instructions, follow your care team, and bring any question about it to your next visit.

Important

The information on this site is for education and does not replace individual medical advice. Always discuss your own treatment with a clinician who knows your case. If this is a medical emergency, contact your local emergency services now.

Sources

Walsh J, Roberts R, Bailey T. Guidelines for insulin dosing in continuous subcutaneous insulin infusion using new formulas from a retrospective study of individuals with optimal glucose levels. J Diabetes Sci Technol 2010;4:1174–1181. doi.org/10.1177/193229681000400516
Joslin Diabetes Center. Insulin stacking. Published 20 November 2019. joslin.org/news-stories/all-news-stories/education/2019/11/insulin-stacking
American Diabetes Association Professional Practice Committee. 6. Glycemic goals, hypoglycemia, and hyperglycemic crises: Standards of Care in Diabetes—2026. Diabetes Care 2026;49(Suppl 1):S132–S149. doi.org/10.2337/dc26-S006
American Diabetes Association. Hypoglycemia (low blood glucose): the 15-15 rule. diabetes.org/living-with-diabetes/treatment-care/hypoglycemia