Basal Insulin Calculator
Estimate your long-acting basal insulin dose from your total daily dose (TDD). Covers multiple split percentages and common long-acting insulin types. Educational use only.
🌙 Basal Dose Estimator
Basal Dose Estimate
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Long-Acting Insulin Types
| Insulin | Brand | Duration | Dosing | Notes |
|---|---|---|---|---|
| Glargine U-100 | Lantus, Basaglar | ~24 hrs | Once daily | Most widely used long-acting; peakless |
| Glargine U-300 | Toujeo | ~36 hrs | Once daily | Flatter profile; less nocturnal hypo |
| Detemir | Levemir | ~18–22 hrs | Once or twice daily | Often needs BID; approved in pregnancy |
| Degludec | Tresiba | >42 hrs | Once daily | Ultra-long; very stable; less dawn effect |
| NPH | Humulin N, Novolin N | ~12–16 hrs | Twice daily | Older; has a peak; more hypo risk |
Basal insulin adequacy is assessed by fasting and between-meal blood glucose. If fasting BG is consistently above target with no food or active bolus explanation, basal may need adjustment. Always adjust with your care team — not based on a single high reading.
How to tell if your basal dose is right
Basal insulin is the steady background dose that holds your glucose level between meals and overnight, while you're not eating. When it's set correctly, your blood sugar should stay relatively flat during a fast — drifting no more than about 30 mg/dL from where it started. If it climbs or falls noticeably when you skip a meal, the basal dose, not your mealtime insulin, is usually the culprit.
Signs your basal may be too high
Unexplained lows between meals or in the early hours, needing to snack to stay safe, or waking overnight sweaty and shaky all point toward too much background insulin. A basal that's too strong forces you to "eat to the insulin," which is the opposite of how it should work.
Signs your basal may be too low
Glucose that creeps upward when you haven't eaten, fasting numbers that are consistently high, or readings that rise overnight suggest the background dose isn't holding the line. The fix is a clinical decision — the trend simply tells you where to look.
When to take long-acting (basal) insulin
Most long-acting insulins are designed for once-daily dosing at the same time each day, and consistency matters more than the exact clock time. Some people split the dose into two to smooth out coverage or curb early-morning rises. Taking it at an erratic time, or missing it, leaves gaps where glucose can climb — which is why a fixed routine, anchored to something you do every day, tends to work best.
Why your basal needs change over time
A basal dose that's perfect today won't necessarily fit in six months. Weight change, activity levels, illness, stress, pregnancy, other medications such as steroids, and the natural progression of diabetes all shift how much background insulin you need. That's why basal isn't a "set and forget" number. Reviewing your fasting and overnight readings periodically — and adjusting only with your care team — keeps the dose matched to your current life rather than your past one.
Frequently Asked Questions
What is basal insulin?
Basal insulin is long-acting insulin that provides a steady background level over roughly 24 hours, covering the glucose your liver releases between meals and overnight. It is separate from bolus (mealtime) insulin.
How do I calculate my basal dose?
A common starting estimate is about 50% of your total daily dose (TDD). For a TDD of 40 units, basal ≈ 20 units. Your care team fine-tunes it from your fasting glucose pattern.
When should I take basal insulin?
Most long-acting insulins are taken once daily at the same time each day. Detemir and NPH are often split into two doses, while degludec's ultra-long action allows flexible timing. Follow your prescribed schedule.
How do I know if my basal dose is right?
Basal is about right when your fasting and between-meal glucose stay stable without food or bolus insulin involved. Consistently high fasting readings may mean basal is too low; overnight lows may mean it is too high — adjust only with your care team.
Sources
- American Diabetes Association. Standards of Medical Care — 2024. Section 9.
- Porcellati F et al. "Glargine vs. NPH insulin in type 1 diabetes." Diabetes Care. 2007.
Last reviewed: June 2025