Premixed to Basal-Bolus Conversion Calculator
Convert a 70/30 or 75/25 premixed regimen into a basal-bolus starting plan — with the safety reduction that makes the switch survivable.
🔄 Conversion Calculator
How the conversion works
A premixed insulin such as 70/30 delivers both components in one fixed ratio at one time. That is its appeal — two injections a day instead of four — and also its limitation, because the mealtime portion arrives whether or not you eat, and the basal portion is tied to the same schedule.
Splitting the regimen separates those jobs. Basal insulin holds glucose steady between meals; rapid-acting insulin covers each meal individually and can be varied or skipped. The conversion is three steps.
Worked example. Someone on 30 units of 70/30 in the morning and 20 in the evening has a TDD of 50 units. Reducing by 15% gives 42.5, rounded to 43 units. A 50/50 split gives roughly 21 units of basal once daily and 22 units of rapid-acting divided across three meals — about 7 units per meal.
Why the dose comes down
The reduction is the part people query, because it looks like undertreating a patient who was already on that total. The logic runs the other way.
In a fixed mix, a share of the dose is compensating for the regimen’s inflexibility rather than the body’s requirement — insulin delivered at a time it is not strictly needed, offset by eating on a schedule that suits the injection. Once basal and mealtime insulin are separated, each component lands where it is actually required, and the same total becomes an excess. Published protocols therefore reduce by 10–20% at the point of switching, and titrate back up from there against readings.
The direction matters for safety. Starting slightly low and titrating up produces mild highs for a few days. Starting at the full previous total produces hypoglycemia, often at night, in someone who has just changed their whole routine and is least able to interpret it.
What changes for the patient
| Premixed 70/30 | Basal-bolus | |
|---|---|---|
| Injections | 2 per day | 4 per day |
| Meal timing | Fixed — meals must match the insulin | Flexible — insulin matches the meal |
| Skipping a meal | Risky; the mealtime portion is already given | Straightforward; omit that bolus |
| Carb counting | Not required | Required for best results |
| Dose adjustment | Both components move together | Basal and mealtime adjusted independently |
| Monitoring | Less frequent | More frequent, especially at first |
The trade is flexibility for effort. It suits someone whose meals vary or who is struggling with post-meal control on a mix; it suits less well someone whose routine is fixed and who finds four injections a burden.
Titrating afterwards
The converted figures are a starting plan, and the two components are adjusted against different data. Basal is titrated against fasting and overnight readings, conventionally no faster than every three days. Mealtime doses are titrated against post-meal readings, meal by meal.
Changing both at once makes neither interpretable — if fasting glucose and post-lunch glucose both move after you adjust both, you cannot tell which change did what. Settle basal first, then work through the meals. Our basal testing guide covers the same principle for pump users, and the reasoning is identical on injections.
Expect the equal thirds not to stay equal. Most people need proportionally more at breakfast, because insulin sensitivity is lowest in the morning.
Limitations & Safety Notes
- This is a starting calculation, not a prescription. The switch changes the amount and timing of every dose and requires prescriber supervision with close early follow-up.
- The 10–20% reduction is a published safety margin, not a precise figure. Individual requirement after conversion is settled by titration.
- Equal thirds across meals is a convention. Most people end up needing proportionally more at breakfast.
- Basal-bolus needs carbohydrate counting and more frequent monitoring to outperform a premix. Without those, the switch may not improve control.
- Titrate basal and mealtime doses separately, against different readings. Changing both together makes the result uninterpretable.
Frequently Asked Questions
How do you convert premixed insulin to basal-bolus?
Add the premixed doses to get the total daily dose, reduce it by 10–20% as a safety margin, then split the remainder — commonly half as basal and half as rapid-acting divided across three meals. The reduction exists because basal-bolus delivers insulin more efficiently than a fixed mix, so the same total would overshoot.
Why reduce the total dose when switching?
A premixed regimen delivers insulin at fixed times whether or not it is needed, so part of the dose is compensating for the inflexibility rather than the body’s requirement. Splitting into basal and mealtime components targets the insulin better, and carrying the full previous total across commonly causes hypoglycemia in the first days.
What split between basal and bolus should I use?
Around 50/50 is the usual starting point, and published guidance places basal anywhere between 40% and 60% of the total with the bolus making up the remainder. Where an individual lands depends on eating pattern and is settled by titration, not by the initial calculation.
How is the bolus portion divided across meals?
The conventional start is equal thirds before breakfast, lunch and evening meal. It rarely stays equal — most people end up needing proportionally more at breakfast because insulin sensitivity is lowest in the morning.
Is 70/30 the same as 75/25?
They are close but not identical. 70/30 is 70% intermediate-acting and 30% rapid or short-acting; 75/25 is 75% and 25%. For conversion purposes the arithmetic starts from the total daily dose either way, so the ratio matters less than the total.
Can I make this switch myself?
No. The conversion changes both the amount and the timing of every dose, and it requires carbohydrate counting, more frequent monitoring and usually more injections. It is a prescriber-led change with close follow-up in the first weeks.
Sources
- American Diabetes Association. Case Series: Premixed Insulin Dosing in Actual Practice. Clinical Diabetes. 2009;27(2):91. Link — how premixed regimens are split in practice.
- American Diabetes Association. 9. Pharmacologic Approaches to Glycemic Treatment: Standards of Care in Diabetes — 2026. Diabetes Care. 2026;49(Suppl 1):S183. Link — basal and prandial dose proportions.
- Endotext / NCBI Bookshelf. Inpatient Diabetes Management. Link — basal-bolus dose distribution.
- BC Diabetes. Converting premixed insulin to basal & rapid insulin. — clinical conversion handout.
Last reviewed: July 2026