NovoLog Dose Calculator
Estimate a mealtime dose of insulin aspart from body weight, and see how its action profile determines when to inject relative to eating.
🍽️ NovoLog Daily Bolus Estimate
What NovoLog does
NovoLog is insulin aspart, a rapid-acting analogue used to cover meals and correct high readings. It begins working in roughly 10 to 20 minutes, peaks around 1 to 3 hours, and is largely finished by 3 to 5 hours.
That profile is what makes basal-bolus therapy work: fast enough to be given at mealtimes, short enough not to overlap heavily with the next meal. It is also why timing matters more for aspart than for any basal insulin — a 15-minute error in a 24-hour insulin is irrelevant, whereas the same error in a 4-hour insulin changes the shape of the whole post-meal curve.
| Property | NovoLog (aspart) | Fiasp (faster aspart) |
|---|---|---|
| Onset | 10–20 minutes | Faster — within minutes |
| Peak | 1–3 hours | Earlier |
| Duration | 3–5 hours | 3–5 hours |
| Typical pre-bolus | 15–20 minutes | 0–10 minutes |
| In-use window | 28 days | 28 days |
Fiasp is the same aspart molecule with added niacinamide to speed absorption. It is not a dose change — it is a timing change.
Where the dose actually comes from
The calculator above estimates the total daily bolus pool from weight, which is useful for setting expectations. It is not how an individual meal dose is worked out.
A mealtime dose has two components. The carbohydrate portion comes from your insulin-to-carb ratio — grams of carbohydrate divided by the ratio. The correction portion comes from your sensitivity factor: current glucose minus target, divided by the ISF, then reduced by any insulin still on board.
Our mealtime dose calculator combines both parts.
Pre-bolus timing
Because aspart takes 10 to 20 minutes to start working and carbohydrate does not wait, injecting as you begin eating puts the two out of step. Evidence on prandial timing supports a 15 to 20 minute head start at a normal starting glucose, which lowers the post-meal peak without increasing hypoglycemia.
Adjust from there: longer if glucose is already high, none at all if it is low or falling, and shorter for a high-fat meal whose carbohydrate arrives late. Our pre-bolus timing guide covers the full set of adjustments.
Limitations & Safety Notes
- The weight-based figure is a total daily bolus pool, not a meal dose. Individual doses come from your carb ratio and correction factor.
- Rapid-acting insulin is timing-sensitive in a way basal insulin is not. The same dose given 20 minutes earlier or later produces a materially different curve.
- Corrections must account for insulin still on board. Stacking corrections is a common cause of delayed hypoglycemia.
- NovoLog does not provide background coverage. It is used alongside a basal insulin, not instead of one.
- Fiasp is faster-absorbing aspart, not stronger aspart. Switching changes pre-bolus timing rather than dose.
Frequently Asked Questions
How do I calculate my NovoLog dose?
A meal dose is the carbohydrate portion (grams divided by your insulin-to-carb ratio) plus any correction ((current glucose minus target) divided by your sensitivity factor), minus insulin still on board. The weight-based figure above estimates only the daily bolus total.
How long before eating should I take NovoLog?
Roughly 15 to 20 minutes at an in-range glucose. Longer if you are starting high, and none at all if you are low or falling — eat first and dose after in that case.
What is the difference between NovoLog and Fiasp?
Fiasp is the same insulin aspart with niacinamide added to speed absorption, so it starts working sooner. The dose is not different; the pre-bolus window is shorter, typically 0 to 10 minutes rather than 15 to 20.
How long does NovoLog last?
Onset is 10 to 20 minutes, peak around 1 to 3 hours, and duration 3 to 5 hours. That duration is what determines insulin on board and how long to wait before correcting again.
Can NovoLog be used as a basal insulin?
No. It is too short-acting to provide background coverage. It is used at meals alongside a long-acting basal, or continuously in a pump where the pump itself supplies the basal rate.
How long does an opened NovoLog vial or pen last?
28 days at room temperature below 86°F, for both vials and pens, after which it should be discarded even if insulin remains.
Sources
- American Diabetes Association. 9. Pharmacologic Approaches to Glycemic Treatment: Standards of Care in Diabetes — 2026. Diabetes Care. 2026;49(Suppl 1):S183. Link — basal initiation and titration principles
- Novo Nordisk. Storage and stability — insulins. Link — NovoLog and Fiasp in-use windows
- Optimal Prandial Timing of Insulin Bolus in Youths with Type 1 Diabetes: A Systematic Review. PMC. Link — pre-bolus timing evidence
Last reviewed: July 2026