Insulin Clinics / Starting and managing

Dosing and adjustment

Insulin doses follow a few principles, not a fixed formula. Understanding the principles helps you read your own numbers — but the specific doses always come from your care team.

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This page describes concepts, not doses. The numbers that work for any individual depend on weight, type of diabetes, kidney function, other medications, eating patterns, and many other factors. Always work with your prescriber on the specific amounts.

Total daily dose

The total daily dose (TDD) is all the insulin a person takes in 24 hours, basal and mealtime combined. For people with type 1 diabetes, a common range is roughly 0.4 to 1.0 units per kilogram of body weight per day, with most adults landing somewhere in the middle. For people with type 2 diabetes, requirements vary much more widely because insulin resistance varies — some people use 0.3 units/kg/day, others over 1.5.

TDD is useful because many other dose calculations are anchored to it. It is also a way to spot when something has changed: if your TDD has been steady for months and suddenly jumps or drops, that is information worth telling the care team.

Basal vs bolus

Insulin replacement mimics two patterns the healthy pancreas produces:

Basal insulin — a slow, steady background amount that keeps fasting and between-meal glucose stable. It also keeps the liver from over-releasing glucose overnight.
Bolus insulin — a quick dose timed with a meal that covers the rise in glucose from food. Bolus insulin also includes "correction" doses to bring down a high reading.

In type 1 diabetes, the basal-bolus split is commonly around 50/50 — about half of the total daily dose is basal, and half is divided across meals. This is a starting estimate, not a rule.

In type 2 diabetes, the picture is different. Most people start on basal alone, often at bedtime, and the basal share of the total dose is much higher — sometimes 100 percent for years. Mealtime insulin is added later only if post-meal numbers are not controlled by basal plus other medications.

Carb counting

Carb counting is the practice of estimating the grams of carbohydrate in a meal so you can match the bolus dose to the food. It applies almost entirely to people taking mealtime (rapid or short-acting) insulin.

The basics:

Carbohydrates raise blood glucose more than protein or fat in the short term, so they are what mealtime insulin is dosed for.
You can read carb counts from packaged food labels, restaurant nutrition information, food databases, or apps. With practice most people get reasonably accurate estimates from familiar meals.
Fiber is sometimes subtracted from total carbs (the "net carb" approach) when fiber is high, because fiber does not raise glucose. Practices vary.
Large amounts of fat or protein in a meal — pizza, burgers, very rich foods — slow digestion and can raise glucose hours later. Pumps offer "extended" or "dual-wave" boluses to handle this; on injections, an extra small dose later sometimes helps.

Carb counting is a learnable skill. Most diabetes education programs teach it explicitly, and CGMs make it much easier to see when an estimate was off.

Insulin-to-carb ratio

An insulin-to-carb ratio (sometimes written I:C or just "carb ratio") tells you how many grams of carbohydrate are covered by one unit of mealtime insulin. A ratio of 1:10 means one unit covers ten grams of carbs; a ratio of 1:15 means one unit covers fifteen grams.

People who are more insulin-sensitive have higher numbers (one unit covers more carbs); people who are more insulin-resistant have lower numbers. Many people have different ratios for different meals — for example, more sensitive at dinner than at breakfast — because the body's response shifts across the day.

Ratios are usually estimated initially using formulas (such as the "500 rule") and then refined based on real-world results over a couple of weeks.

Correction factor (insulin sensitivity factor)

A correction factor, also called insulin sensitivity factor (ISF), tells you how far one unit of mealtime insulin will lower your blood glucose. A correction factor of 50 means one unit lowers blood glucose by about 50 mg/dL.

The correction factor is used to calculate small extra doses when blood glucose is above the target. For example, if your target is 120, your reading is 220, and your correction factor is 50, the math suggests two units to bring you back. As with carb ratios, correction factors are estimates that are tuned over time, and they may differ at different times of day.

Stacking. Rapid-acting insulin keeps working for 3–5 hours after the dose. Adding more correction insulin while a previous dose is still active is called "stacking" and is the most common cause of unexpected lows. Most pumps and many apps track "insulin on board" to help avoid this. On injections, a useful rule is to wait at least 3–4 hours between corrections unless something has changed.

What titration looks like

Titration is the process of adjusting an insulin dose based on patterns. The principles are simple even though the calculations are not.

Adjust based on patterns, not single readings

One high reading on Tuesday morning is not enough to change a dose. The same high reading three or four mornings in a row is. Most clinicians look at three to seven days of data before changing anything, unless readings are clearly dangerous.

Change one thing at a time

If both basal and mealtime doses might need adjusting, the basal usually gets fixed first — because basal sets the baseline that mealtime doses are layered on top of. Trying to adjust two doses at once makes it impossible to tell which change did what.

Use small steps

For basal insulin, common adjustments are 1–2 units at a time, or about 10 percent of the current dose, every few days, based on fasting glucose. For mealtime insulin, the change is often 0.5–1 unit per meal at a time. Larger jumps overshoot and produce lows.

Look at the right reading for the right dose

Fasting glucose mostly reflects basal insulin (and overnight liver glucose release).
Pre-lunch glucose mostly reflects breakfast bolus.
Pre-dinner glucose mostly reflects lunch bolus.
Bedtime glucose mostly reflects dinner bolus.
2-hour post-meal glucose reflects how well that meal's bolus matched the meal.

This is why clinicians often ask for paired pre- and post-meal readings — the difference is more informative than either number alone.

"Sliding scale" is not the same as titration

You may hear the term sliding scale, which refers to a fixed table of correction doses based on the current blood glucose reading. Sliding scale alone, without basal insulin or attention to meals, is widely considered poor practice for ongoing care of type 2 diabetes — it reacts to highs after they happen instead of preventing them. It is still used in some hospital settings, where the situation changes hour to hour.

Putting it together

For someone on basal-bolus therapy, a typical day's thinking goes:

Take basal insulin at the same time each day to anchor the baseline.
Before each meal, check glucose, estimate carbs, and dose mealtime insulin using the carb ratio plus a correction if above target.
Watch readings over the following hours; note patterns, not isolated numbers.
Adjust doses with the care team every 1–4 weeks, one variable at a time, in small steps.

For someone on basal alone, the same logic applies, but only the basal dose is being adjusted, usually based on fasting numbers.

What changes the right dose

Even a perfectly titrated regimen will need to adapt to:

Illness. Infections raise insulin needs, sometimes dramatically.
Stress. Cortisol and adrenaline raise glucose. A demanding work week can shift averages noticeably.
Activity. Exercise lowers insulin needs both during and afterward, sometimes for hours.
Weight change. Gaining or losing weight changes insulin sensitivity, often substantially.
Other medications. Steroids raise glucose; some weight-loss and diabetes medications lower it.
Hormones. Menstrual cycles, pregnancy, and menopause all shift insulin requirements.

None of these are failures of the plan. They are exactly what insulin therapy is designed to handle, with help.