Insulin Types Explained: Onset, Peak & Duration
Medically reviewed by Dr. Chhaya Makhija, MD, DipABLM — September 2026
By Ryan Mitchell · Medically reviewed by Dr. Chhaya Makhija, MD, DipABLM · Updated July 2026
Every insulin does the same job — moving glucose out of the blood — but the five classes differ in when they start (onset), when they work hardest (peak), and how long they last (duration). Those three numbers decide what role each insulin plays in a regimen, which dosing rule applies to it, and how it interacts with meals and corrections.
The complete onset–peak–duration chart
| Class | Generic (brand) | Onset | Peak | Duration | Role |
|---|---|---|---|---|---|
| Ultra-rapid | faster aspart (Fiasp), lispro-aabc (Lyumjev) | 2–15 min | ~1 h | 3–5 h | Mealtime bolus, minimal pre-bolus |
| Rapid-acting | lispro (Humalog), aspart (NovoLog), glulisine (Apidra) | 10–20 min | 1–2 h | 3–5 h | Mealtime bolus & corrections (500/1800 Rules) |
| Short-acting (Regular) | Humulin R, Novolin R | 30–60 min | 2–4 h | 6–8 h | Meals with 30-min lead (450/1500 Rules); IV drips |
| Intermediate | NPH (Humulin N, Novolin N) | 1–2 h | 4–8 h | 12–18 h | Twice-daily basal in some regimens |
| Long-acting | glargine (Lantus, Basaglar), detemir (Levemir) | 1–2 h | Minimal / flat | ~20–24 h | Once/twice-daily basal |
| Ultra-long | degludec (Tresiba), glargine U-300 (Toujeo) | 1–6 h | None (flat) | 36–42 h | Once-daily basal, flexible timing |
Why the times matter for dosing math
- Which carb-ratio rule applies. Rapid analogs use the 500 Rule; Regular insulin's longer overlap uses the 450 Rule.
- Pre-bolus timing. Rapid insulin is typically taken 10–20 minutes before eating; Regular needs ~30 minutes. Our timing calculator adjusts for your current glucose.
- Insulin on board. Duration defines how long a bolus keeps working — the basis of IOB calculations and stacking prevention. Rapid analogs are usually modeled at 3–5 hours.
- Hypo-risk windows. Peaking insulins (NPH, Regular) create predictable low-risk windows; flat basals don't. This is why NPH regimens require more structured meal timing.
Premixed insulins
Premixed products (70/30, 75/25, 50/50) combine intermediate insulin with rapid or Regular insulin in one injection — e.g., Humulin 70/30 is 70% NPH + 30% Regular. They trade flexibility for simplicity: fewer injections, but meals must be consistent because the mix can't be adjusted per-meal. Dosing conversions between regimens are care-team territory.
Concentrations: U-100, U-40, U-500
Most human insulin is U-100 (100 units/mL). U-500 Regular exists for severe insulin resistance, and U-40 is common in veterinary insulin (see the cat and dog calculators). Matching syringe to concentration is a safety-critical step — our units-to-mL converter and syringe-reading guide cover it in detail.
Frequently Asked Questions
How long does rapid-acting insulin take to work?
Rapid-acting analogues such as lispro, aspart and glulisine generally begin working within about 15 minutes, peak around 1–2 hours, and are largely finished by 4–5 hours. Ultra-rapid formulations act sooner still. Regular human insulin is slower on every count, typically starting around 30 minutes and peaking at 2–3 hours.
What is the difference between basal and bolus insulin?
Basal insulin is the background supply that holds glucose steady between meals and overnight, delivered by a long-acting insulin or a pump’s continuous rate. Bolus insulin is the fast-acting dose taken to cover a meal or correct a high reading. A common starting split is roughly half the total daily dose as basal and half as bolus.
What does U-100 mean?
It is the concentration: 100 units of insulin per millilitre, which is the standard for human insulin products. U-40 holds 40 units per mL and is mostly veterinary, while U-500 is five times as concentrated as U-100 and reserved for severe insulin resistance. Mismatching concentration and syringe is a well-documented cause of serious dosing errors.
What are premixed insulins?
They combine a fixed proportion of intermediate and rapid or short-acting insulin in one pen or vial — 70/30 and 75/25 are common. They reduce the number of daily injections, which suits some people, but the fixed ratio cannot be adjusted independently, so mealtime flexibility is lower than with a separate basal-bolus regimen.
Why does duration of action matter for dosing?
Because doses overlap. If a previous rapid-acting dose is still active and you take another correction, the two stack and can drive glucose too low. Knowing how long your insulin actually works is what makes insulin-on-board calculations meaningful.
Sources & References
- American Diabetes Association. Standards of Care in Diabetes — 2026. Section 9. Link
- NIDDK. Insulin Medicines & Treatments. Link
- Donner T, Sarkar S. Insulin – Pharmacology, Therapeutic Regimens. In: Endotext. Link
Written by Ryan Mitchell · Last updated: September 2026