Basal-Bolus Insulin Calculator
Medically reviewed by Dr. Chhaya Makhija, MD, DipABLM — October 2026
Estimate your full basal-bolus regimen from TDD — basal dose, mealtime bolus, carb ratio (ICR), sensitivity factor (ISF), and correction dose. Uses the ADA's roughly half-and-half split with the 500 and 1800 rules. Educational use only.
⚖️ Full Basal-Bolus Estimator
Don't know your TDD? Calculate TDD →
Optional: enter current BG to calculate correction dose
Full Regimen Estimates
units/day
(equal meals)
g carbs per unit
mg/dL per unit
How a Basal-Bolus Regimen Works
Basal Insulin (40–50% of TDD)
Long-acting insulins (glargine/Lantus, degludec/Tresiba, or detemir/Levemir where still available) are given once or twice daily to suppress hepatic glucose output between meals and overnight. The dose keeps blood glucose stable during fasting. If fasting or overnight glucose is consistently high, basal may be too low; if hypoglycemia occurs between meals, basal may be too high.
Bolus (Mealtime) Insulin
Rapid-acting analogs are given at mealtime to cover the carbohydrate content of the meal. If all meals are equal in carbs, the bolus pool (TDD × 50%) can be divided equally. In real practice, meal bolus varies by what you eat — hence the importance of knowing and applying your ICR.
Correction Dose
Added to the meal bolus when pre-meal BG is above target. A negative correction (BG below target) would reduce the bolus — but never give less than zero. Always subtract IOB before applying a standalone correction.
Basal-to-Bolus Ratio: 50/50, 40/60 and What the Evidence Shows
When a different split makes sense
The ADA Standards of Care 2026 start both outpatient type 1 regimens and hospital basal-bolus plans at roughly half basal, half mealtime. Measured needs often land below 50% basal, and the ADA warns about overbasalization: too much basal insulin quietly covers meals, masks a wrong carb ratio and raises the risk of lows between meals and overnight. People eating low-carb can drift the other way, toward a larger basal share. Your split is a setting your care team titrates, not a constant.
| Context | Typical split | Why |
|---|---|---|
| Outpatient type 1 start | ≈ 50 / 50 | ADA Standards of Care 2026 |
| Patient teaching (UCSF) | 40–50 basal | UCSF Diabetes Teaching Center |
| Davidson AIM analysis | 47 basal | 167 well-controlled type 1 adults (Endocr Pract 2008) |
| Type 1 on a pump, measured | ≈ 28–30 basal | Kuroda et al., Diabetes Care 2011 |
| Hospital, eating meals | ≈ 50 / 50, plus correction | ADA 2026 hospital standards; RABBIT 2 trial |
| Low-carb eaters | 55–60 basal | Less carbohydrate to cover at meals |
Transitioning from IV insulin (drip) to basal-bolus
Hospital patients coming off an insulin infusion are converted using the drip's own data: total the last 6–8 hours of stable infusion, extrapolate to 24 h, then take about 60% of that as the starting subcutaneous TDD (ADA 2026), split basal/bolus. Give the basal dose about 2 hours before the drip stops; the 2024 hyperglycemic-crises consensus says at least 1–2 hours. Our Drip → Subcutaneous Calculator runs this exact conversion. Every number in a basal-bolus plan can be checked with the insulin regimen calculators on our home page.
Titrating each component separately
- Fasting/overnight high or low → adjust basal (classic pattern: ±2 u every 3 days to fasting target).
- Post-meal spikes → adjust that meal's ICR, not the basal.
- Corrections consistently over/under-shooting → adjust ISF.
- Change one variable at a time and give it 3 days of data — otherwise you can't attribute the result.
How to Calculate Basal and Bolus Doses: Worked Example
Take an adult with type 1 diabetes, 70 kg, starting a basal-bolus plan at the ADA's typical 0.5 u/kg/day.
| Step | Formula | Result |
|---|---|---|
| 1. Total daily dose | 70 kg × 0.5 | 35 units/day |
| 2. Basal dose | 35 × 50% | 17.5 → 17 or 18 units once daily |
| 3. Bolus pool | 35 − 17.5 | 17.5 units across the day's meals |
| 4. Carb ratio | 500 ÷ 35 | 1 unit per 14 g carbohydrate |
| 5. Correction factor | 1800 ÷ 35 | 1 unit lowers glucose ≈ 51 mg/dL (2.9 mmol/L) |
| 6. Lunch bolus, 60 g carbs | 60 ÷ 14 | 4.3 units |
| 7. Correction at 200 mg/dL, target 120 | (200 − 120) ÷ 51 | 1.6 units |
| 8. Total lunch dose | 4.3 + 1.6 | ≈ 6 units (minus any insulin still on board) |
Each number is a starting estimate. Fasting readings then tune the basal dose, post-meal readings tune the carb ratio, and correction results tune the correction factor.
Basal-Bolus Insulin Calculator: Limitations & Safety Notes
- The 50/50 basal-to-bolus split is a convention rather than a rule. 40/60 and 60/40 are both used routinely depending on eating pattern and regimen.
- The calculation assumes a full basal-bolus regimen. It does not apply to someone on basal insulin alone, where the dose is titrated against fasting glucose.
- Converting from an intravenous infusion needs overlap timing as well as a dose figure — subcutaneous basal must be given before the drip stops.
- Each component is titrated against different data: basal against overnight and fasting readings, bolus against post-meal readings. Adjusting both at once makes neither interpretable.
Sources & References
- American Diabetes Association. Standards of Care in Diabetes — 2026. Link
- Walsh J, Roberts R, Bailey T. "Guidelines for Optimal Bolus Calculator Settings." J Diabetes Sci Technol. 2011;5(1):129–135.
- Umpierrez GE, et al. RABBIT 2 Trial: basal-bolus vs sliding scale in inpatients with type 2 diabetes. Diabetes Care. 2007;30(9):2181-6. Link
- American Diabetes Association. 16. Diabetes Care in the Hospital: Standards of Care in Diabetes — 2026. — source of the half basal / half nutritional split, the 60% IV-to-SC conversion and the 2-hour overlap. Link
- Davidson PC, Hebblewhite HR, Steed RD, Bode BW. "Analysis of guidelines for basal-bolus insulin dosing." Endocr Pract. 2008;14(9):1095–1101. Link
- UCSF Diabetes Teaching Center. Calculating Insulin Dose. Link
- Kuroda A, et al. "Basal Insulin Requirement Is ∼30% of the Total Daily Insulin Dose in Type 1 Diabetic Patients Who Use the Insulin Pump." Diabetes Care. 2011;34(5):1089. Link
Written by Ryan Mitchell · Last updated: October 2026
How basal-bolus mimics a working pancreas
A healthy pancreas does two jobs at once. It releases a small, steady trickle of insulin all day to manage the glucose your liver constantly produces, and it adds a sharp burst whenever you eat. A basal-bolus regimen copies that pattern with two kinds of insulin: a long-acting basal dose for the background trickle, and a rapid-acting bolus for each meal. Because the two roles are separated, you can fine-tune one without disturbing the other — something a single fixed dose can never do.
This is why basal-bolus is considered the most physiological way to use insulin outside of a pump. It matches insulin to what your body is actually doing moment to moment, rather than forcing your meals and routine to fit a rigid dose.
Splitting your total daily dose between basal and bolus
The usual starting point is to divide your total daily dose roughly in half: about 50% as basal and 50% spread across mealtime boluses. The bolus portion is then shared between meals according to how many carbohydrates each contains, using your insulin-to-carb ratio.
Why the 50/50 split is only a starting point
Your ideal balance depends on how you eat and live. People who eat lower-carb often need a larger basal share; those who eat large, frequent meals may need more bolus. The split is refined over time by watching whether your glucose drifts while fasting (a basal issue) or spikes after meals (a bolus issue). The calculator gives you a sensible first estimate; your data and your care team shape the rest.
Why basal-bolus offers more flexibility than fixed doses
The biggest practical win of basal-bolus is freedom. Because each meal's dose is calculated from what you're actually eating, you can change meal sizes, eat later, skip a meal, or adjust for exercise without throwing your whole day off. Fixed-dose regimens, by contrast, demand that you eat set amounts at set times to match the insulin you've already taken. For most people who want their diabetes to fit around their life — rather than the reverse — that flexibility is the deciding advantage.
Converting premixed (mixed) insulin to a basal-bolus regimen
People switching from a premixed insulin (like 70/30, 75/25 or 50/50, taken twice daily) to full basal-bolus need to split that fixed mixture back into separate long-acting and mealtime components. The usual starting approach keeps the same total daily dose and redistributes it:
| Step | What to do | Example (premixed TDD 40 u) |
|---|---|---|
| 1. Keep total | Add up all premixed units per day → that becomes the new TDD | 24 u AM + 16 u PM = 40 u |
| 2. Set basal | ~50% of TDD as one long-acting dose | 20 u glargine once daily |
| 3. Split bolus | Remaining ~50% divided across 3 meals | ~6–7 u rapid-acting per meal |
| 4. Refine | Titrate basal by fasting glucose, meals by post-meal readings | Adjust over 1–2 weeks |
Some clinicians reduce the total by 10–20% during the switch to lower early hypoglycemia risk, then titrate up. This is a supervised change — the numbers above are a starting framework, not a prescription. Related: long-acting (basal) calculator and carb-ratio calculator for the mealtime side.
Frequently Asked Questions: Basal-Bolus Insulin Calculator
What is a basal-bolus insulin regimen?
A basal-bolus regimen uses two types of insulin to mimic normal pancreatic function. Basal (long-acting) insulin covers background glucose needs between meals and overnight — suppressing liver glucose output. Bolus (rapid-acting) insulin is given before meals to cover carbohydrates and, when needed, to correct high blood glucose. This is the standard regimen for Type 1 diabetes and is increasingly used for intensively managed Type 2 diabetes.
How is basal insulin calculated?
Basal dose is typically estimated as 40–50% of TDD. With TDD = 40 units, basal = 20 units/day. The basal dose is given as long-acting insulin (glargine/Lantus, degludec/Tresiba, or detemir/Levemir where still available). Basal adequacy is assessed by looking at fasting and between-meal blood glucose — if these are in range, basal is appropriate. Adjustment is guided by glucose patterns under your care team's supervision.
What is the difference between basal and bolus insulin?
Basal insulin (long-acting: glargine, detemir, degludec) provides a steady low-level insulin background, given once or twice daily. It covers glucose that the liver produces during fasting. Bolus insulin (rapid-acting: lispro, aspart, glulisine) is given before meals, peaks quickly (30–90 min), and covers carbohydrate-driven glucose rises. Basal controls fasting glucose; bolus controls post-meal glucose. Both are necessary for complete insulin replacement in Type 1 diabetes.
Can I mix basal and bolus insulin?
It depends on the insulin types. Glargine (Lantus/Basaglar/Toujeo) and degludec (Tresiba) must NOT be mixed with other insulins — mixing changes their pharmacokinetics and can cause unpredictable action. NPH (intermediate-acting) can be mixed with Regular or some rapid-acting analogs in the same syringe. Pre-mixed insulins (e.g., 70/30) are pre-formulated blends. Always follow your prescriber's specific instructions for mixing — never combine insulins without explicit guidance.
What is the normal basal to bolus ratio?
Starting plans use roughly 50% basal and 50% bolus, per the ADA Standards of Care 2026, and patient guides give 40–50% basal. Measured needs vary: one study of well-controlled type 1 adults found 47% basal, and a study of pump users found about 28%. A basal share well above 50% often means mealtime doses are too small.
How do I calculate my bolus dose?
Divide the meal's carbohydrate grams by your carb ratio, then add a correction if your glucose is above target: (current − target) ÷ correction factor. With a 1:14 ratio, 60 g of carbs is 4.3 units; at 200 mg/dL with a target of 120 and a factor of 51, add 1.6 units, for about 6 units in total. Subtract insulin still on board.