Basal Percentage Calculator
See what percent of your total daily dose is basal insulin, or split a TDD into basal and bolus at a target percentage — a quick check on whether your basal share is in the usual range.
How to Use This Calculator
- Choose a mode — find your basal % (enter basal + TDD), or split TDD by a target % (enter TDD + %).
- Enter the values for that mode.
- Read the result: your basal share and bolus share, or the basal/bolus units for your target split.
This is a ratio check, not a dosing instruction. A basal share well outside ~40–60% is worth reviewing with your care team.
Basal as a Share of Total Daily Dose
In a basal-bolus regimen, roughly half your insulin is usually basal (background) and half is bolus (meals and corrections). Checking your basal percentage helps spot an imbalance — for example, too much basal can cause between-meal or overnight lows.
Example: 20 units basal on a TDD of 40 → 20 ÷ 40 × 100 = 50% basal.
Typical Basal Percentages
| Basal share of TDD | Interpretation |
|---|---|
| 40–50% | Common target for many adults |
| 50–60% | Sometimes used with lower-carb intake |
| > 60% | High basal share — check for between-meal lows |
| < 40% | Low basal share — check for fasting highs |
Children, very active people, and specific insulins can shift the ideal split. Personal data matters most.
What Changes Your Ideal Basal Split
Diet and activity
Your basal share shifts with how you eat and move. A lower-carb diet means smaller meal boluses, so basal becomes a larger percentage of TDD (sometimes 50–60%+). Frequent exercise can lower overall needs and may call for less basal at certain times, while grazing or high-carb eating raises the bolus share.
Signs your basal share is off
Too much basal shows up as lows when you skip or delay a meal, or overnight. Too little basal shows up as a glucose rise while fasting or overnight even without eating. The way to check is a fasting basal test, where stable glucose during a fast suggests the basal is about right.
Frequently Asked Questions
What percentage of TDD should be basal?
A common starting point is about 40–50% of total daily dose as basal, with the rest as bolus. The ideal split depends on your eating pattern, activity, and insulin type, so it's individualised with your care team.
How do I calculate my basal percentage?
Divide your basal units by your total daily dose and multiply by 100. For example, 20 units of basal on a 40-unit TDD is a 50% basal percentage.
What if my basal percentage is too high?
A high basal share (well over 60%) can cause lows when you skip meals or overnight. A basal rate test can check this. Any adjustment should be made with your clinician — see our basal rate testing helper.
How is this different from a basal insulin calculator?
A basal insulin calculator estimates a basal dose from TDD. This tool focuses on the percentage relationship — checking your current basal share or splitting TDD by a chosen percentage.
How do I know if my basal dose is right?
The basal dose is about right when, in the absence of food, bolus insulin and heavy exercise, your glucose stays roughly steady — generally within about 30 mg/dL. A glucose rise while fasting suggests too little basal; a fall suggests too much. A structured fasting basal test, done with your care team, is how this is checked.
Does a low-carb diet change my basal percentage?
Usually yes. Eating fewer carbs means smaller mealtime boluses, so basal makes up a larger share of your total daily dose — often above 50%. The absolute basal dose may not change much; it's the bolus side that shrinks. Any dose changes should be guided by your care team.
Sources
- American Diabetes Association. Standards of Care — insulin regimens and basal-bolus therapy.
- Walsh J, Roberts R. Pumping Insulin. Basal-bolus balance.
Last reviewed: June 2025