NovoLog Dose Calculator
Medically reviewed by Dr. Chhaya Makhija, MD, DipABLM — October 2026
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 |
| When to inject (label) | 5–10 minutes before a meal | At the start of a meal or within 20 minutes after |
| 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. The NovoLog label says to inject within 5–10 minutes before a meal. Studies of prandial timing, mostly in young people with type 1 diabetes, found that a longer head start of 15 to 20 minutes lowers the post-meal peak further; agree any longer gap with your care team.
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. Basal and supply tools for aspart users are in our NovoLog and insulin calculators.
NovoLog is the US brand of insulin aspart; outside the US the same insulin is sold as NovoRapid, and the dosing information on this page applies to both names.
NovoLog Label Rules: Pens, Pumps and Mixing
- Forms: 10 mL vial, FlexPen and FlexTouch prefilled pens, and PenFill cartridges, all U-100. The pens dial in 1-unit steps.
- Pumps: change the NovoLog in the reservoir at least every 7 days, and keep it below 98.6 °F (37 °C). Insulin taken from a vial for pump use has a total in-use time of 19 days.
- Mixing: NovoLog may be mixed only with NPH in a syringe. Draw NovoLog first and inject straight away. Never mix it with anything in a pump.
- Diluting: with the maker's diluting medium, NovoLog can be diluted to U-10 or U-50 for very small doses, under medical supervision.
- Action: the label puts the peak effect at 1–3 hours and the duration at 3–5 hours.
NovoLog correction chart (sliding scale by sensitivity factor)
A NovoLog correction scale is not one fixed table that suits everyone. It is generated from your own sensitivity factor, which the 1800 Rule estimates by dividing 1800 by your total daily dose. The table below shows what that produces, with a worked correction from a reading of 250 mg/dL down to a target of 120.
| TDD (units/day) | Sensitivity factor (1800 Rule) | Same factor in mmol/L | Correction, 250 to 120 |
|---|---|---|---|
| 30 | 60 mg/dL | 3.3 mmol/L | 2.2 units |
| 40 | 45 mg/dL | 2.5 mmol/L | 2.9 units |
| 50 | 36 mg/dL | 2 mmol/L | 3.6 units |
| 60 | 30 mg/dL | 1.7 mmol/L | 4.3 units |
| 80 | 22.5 mg/dL | 1.3 mmol/L | 5.8 units |
| 100 | 18 mg/dL | 1 mmol/L | 7.2 units |
Two things follow. A higher daily dose produces a smaller sensitivity factor, so each unit moves glucose less and the corrections get larger. And a scale built around one daily total stops fitting once that total changes, which is why a printed scale goes stale after a regimen is adjusted.
A scale written for a different insulin does not transfer. NovoLog is a rapid-acting analogue, while regular human insulin acts more slowly and peaks later. A grid written for one can mistime doses when used with the other, so check which insulin a scale names before following it.
NovoLog Dose Calculator: 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: NovoLog Dose Calculator
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?
The NovoLog label says within 5 to 10 minutes before a meal. Some care teams advise 15 to 20 minutes when glucose is in range, based on timing studies. If you are low or falling, eat first and dose after.
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, but the timing is: the Fiasp label says to inject at the start of a meal or within 20 minutes after starting it, while NovoLog goes in 5 to 10 minutes before.
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
- Novo Nordisk. NovoLog (insulin aspart) prescribing information, revised 02/2023. Link
- Novo Nordisk. Fiasp (insulin aspart) prescribing information, revised 06/2023. Link
Written by Ryan Mitchell · Last updated: October 2026