Insulin Dose Calculator
The complete dosing walkthrough: estimate your total daily dose (TDD) from weight, split it into basal and bolus, and derive your insulin-to-carb ratio (500 Rule) and correction factor (1800 Rule) — with every formula shown.
💉 Full Insulin Dose Calculator
Estimated Results
Estimated Total Daily Dose (TDD)
(long-acting)
(across meals)
X g carbs (500 Rule)
BG by X mg/dL (1800 Rule)
How to Use This Calculator
Enter Weight
Type your weight in kg or lbs — the value converts automatically when you toggle units.
Pick a Dose Factor
0.5 u/kg is the ADA midpoint for most adults. Insulin-naïve Type 2 usually starts at 0.2 u/kg.
Choose the Split
50/50 is the common teaching default; some clinicians prefer 40% basal / 60% bolus.
Read All Four Numbers
TDD, basal dose, ICR and ISF are calculated together — the same chain your care team uses.
Check the Formulas
Every step of the math is printed below the result so you can verify or share it.
Confirm With Your Team
These are population starting estimates. Your provider confirms, adjusts, and titrates them.
The Complete Insulin Dosing Chain, Explained
Clinicians estimate insulin doses in a chain of four linked calculations. Each step feeds the next, which is why this page calculates them together rather than in isolation.
Step 1 — Total Daily Dose (TDD)
Worked example: 75 kg × 0.5 = 37.5 units/day. Insulin-naïve Type 2: 75 × 0.2 = 15 u/day (or a fixed 10 u basal start). Explore this step in depth with the Dose by Weight Calculator or TDD Calculator.
Step 2 — Basal / Bolus Split
Worked example: 37.5 u TDD → basal ≈ 19 u once daily (long-acting), bolus pool ≈ 18.5 u divided across meals. See the Basal-Bolus Calculator for regimen details.
Step 3 — Insulin-to-Carb Ratio (500 Rule)
Worked example: 500 ÷ 37.5 ≈ 1 unit per 13 g carbs. A 65 g-carb meal → 65 ÷ 13 = 5 units. Using Regular insulin? Use the 450 Rule instead. Full detail: ICR Calculator.
Step 4 — Insulin Sensitivity Factor (1800 Rule)
Worked example: 1800 ÷ 37.5 = 48 mg/dL per unit. At 220 mg/dL with a 120 target: (220 − 120) ÷ 48 ≈ 2 units correction — minus any insulin on board. Full detail: ISF Calculator and Correction Dose Calculator.
Titration: where the real dose comes from
Weight-based math produces a starting estimate only. The actual working dose emerges over 2–6 weeks of titration: fasting glucose guides basal adjustments (a common outpatient pattern is +2 units every 3 days until fasting glucose is in target, per ADA guidance), while post-meal readings refine the ICR, and correction outcomes refine the ISF. Expect your care team to adjust each number independently — most people do not end up on exactly the formula values.
Renal impairment, steroid therapy, pregnancy, and pediatric care all change these formulas materially. Use the dedicated tools: pediatric, pregnancy, steroid-induced hyperglycemia.
Quick Reference: Starting TDD by Body Weight
Estimates from the ADA starting range (0.4 / 0.5 / 0.6 u/kg/day). Values rounded to the nearest unit.
| Weight (kg) | Weight (lbs) | Low — 0.4 u/kg | Mid — 0.5 u/kg | High — 0.6 u/kg |
|---|---|---|---|---|
| 50 | 110 | 20 u | 25 u | 30 u |
| 60 | 132 | 24 u | 30 u | 36 u |
| 70 | 154 | 28 u | 35 u | 42 u |
| 80 | 176 | 32 u | 40 u | 48 u |
| 90 | 198 | 36 u | 45 u | 54 u |
| 100 | 220 | 40 u | 50 u | 60 u |
| 110 | 243 | 44 u | 55 u | 66 u |
| 120 | 265 | 48 u | 60 u | 72 u |
Limitations & Safety Notes
- The 500/1800 Rules assume rapid-acting analog insulin. Regular insulin uses the 450/1500 Rules.
- Formulas do not account for insulin on board, activity, illness, alcohol, or gastroparesis.
- Do not apply adult formulas to children — pediatric dosing requires specialist supervision.
- Renal or hepatic impairment reduces insulin clearance; standard formulas may overestimate need.
Sources & References
- American Diabetes Association. Standards of Medical Care in Diabetes — 2024. Section 9: Pharmacologic Approaches. Link
- Walsh J, Roberts R. Using Insulin: Everything You Need for Success with Insulin. (Origin of the 500/1800 Rules.)
- Davidson PC, et al. Analysis of guidelines for basal-bolus insulin dosing. Endocr Pract. 2008.
- NIDDK. Insulin Medicines & Treatments. Link
Last reviewed: July 2026 · See our methodology
Frequently Asked Questions
How do I calculate my insulin dose?
Start with total daily dose: weight (kg) × 0.4–0.6 u/kg/day. Split it ~50% basal / 50% bolus. Then derive your carb ratio (500 ÷ TDD) and correction factor (1800 ÷ TDD). Each meal dose = carbs ÷ ICR, plus (current − target BG) ÷ ISF when above target. Confirm every value with your care team before use.
What is the 500 Rule and the 1800 Rule?
The 500 Rule (500 ÷ TDD) estimates how many grams of carbohydrate one unit of rapid-acting insulin covers. The 1800 Rule (1800 ÷ TDD) estimates how far one unit drops blood glucose in mg/dL. Regular insulin uses the 450 and 1500 Rules instead — see our 450 Rule calculator.
How much insulin do I need per day?
Typical adult starting estimates are 0.4–0.6 units/kg/day — 28–42 units for a 70 kg adult. Insulin-naïve Type 2 patients usually begin far lower (0.2 u/kg or 10 units basal). People with significant insulin resistance may need considerably more over time. The starting number is only a launch point for supervised titration.
What is the difference between basal and bolus insulin?
Basal insulin is the long-acting background dose (40–50% of TDD) covering fasting periods and overnight. Bolus insulin is rapid-acting insulin at meals covering carbohydrates and corrections (the remaining 50–60%, split across meals). Our basal-bolus calculator models the full regimen.
Is this calculator safe to use for dosing decisions?
It is an educational tool showing the standard published formulas so you can understand where your prescribed numbers come from. It is not a dosing device and not medical advice. Never start or change insulin without your doctor or diabetes care team.