NPH Insulin Dose Calculator
Medically reviewed by Dr. Chhaya Makhija, MD, DipABLM — October 2026
Estimate a starting NPH (Humulin N or Novolin N) dose from body weight or from your current long-acting insulin, and split it between breakfast and bedtime. Educational use only.
🧮 NPH Dose Estimator
NPH Dose Estimate
units
units
What NPH insulin is
NPH (neutral protamine Hagedorn) is an intermediate-acting human insulin. The brands are Humulin N from Lilly and Novolin N from Novo Nordisk, and NPH is also the long-acting part of 70/30 and 50/50 premixed insulins. Protamine slows absorption, which makes NPH a cloudy suspension rather than a clear solution.
| Property | NPH (Humulin N, Novolin N) |
|---|---|
| Starts working | 1–2 hours |
| Peak effect | 4–8 hours |
| Lasts | 12–18 hours |
| Usual schedule | Twice daily, or once at bedtime |
| Appearance | Cloudy; mix gently before every dose |
The peak is what sets NPH apart. A morning dose peaks around lunch and helps cover it; an evening dose peaks overnight. That peak is also the main source of NPH-related lows, which is why the timing of the second dose matters. The long-acting insulin calculator compares NPH with peakless basal insulins such as glargine and degludec.
Starting NPH dose by weight
The American Diabetes Association suggests starting basal insulin at 10 units a day or 0.1 to 0.2 units per kg per day, then adjusting every few days from fasting glucose. When NPH is given twice daily, a common split is two-thirds before breakfast and one-third at bedtime.
| Body weight | 0.1 units/kg/day | 0.2 units/kg/day | 0.2 units/kg split (breakfast + bedtime) |
|---|---|---|---|
| 50 kg (110 lb) | 5 units | 10 units | 7 + 3 units |
| 60 kg (132 lb) | 6 units | 12 units | 8 + 4 units |
| 70 kg (154 lb) | 7 units | 14 units | 9 + 5 units |
| 80 kg (176 lb) | 8 units | 16 units | 11 + 5 units |
| 90 kg (198 lb) | 9 units | 18 units | 12 + 6 units |
| 100 kg (220 lb) | 10 units | 20 units | 13 + 7 units |
| 120 kg (265 lb) | 12 units | 24 units | 16 + 8 units |
Doses are rounded to whole units. Your prescriber chooses the factor; older adults and people prone to lows usually start at the lower end.
Why the evening dose usually goes at bedtime
Given with dinner, evening NPH tends to peak in the early hours of the night, when glucose is naturally lowest. Moving the dose to bedtime shifts the peak to the early morning, where it meets the natural pre-dawn rise in glucose instead. Many care teams use bedtime dosing for this reason, especially after an overnight low.
Switching between NPH and long-acting insulin
| Switch | Typical starting dose | Basis |
|---|---|---|
| Twice-daily NPH → once-daily glargine (Lantus) | About 80% of the total NPH dose | Lantus prescribing information |
| Once-daily NPH → once-daily glargine | Same dose | Lantus prescribing information |
| NPH → degludec (Tresiba) | Same total daily units | Tresiba prescribing information |
| Glargine or degludec → NPH | Often 80% of the total, split twice daily | Common hospital protocol; prescriber decides |
When switching to NPH, many protocols cut the total by about a fifth, because NPH's peak adds overnight-low risk that a peakless insulin does not carry. For the opposite move, the Lantus dose calculator covers starting glargine. Analog basal and mealtime tools are grouped in our insulin regimen calculators.
Where NPH is still used
- Cost. Human insulins such as NPH cost far less than analog insulins, and in most US states they can be bought without a prescription.
- Premixed insulin. 70/30 is 70% NPH and 30% regular insulin. The premixed to basal-bolus calculator converts a 70/30 dose into separate basal and mealtime doses.
- Steroid-induced high glucose. A morning NPH dose matches the daytime glucose rise from once-daily prednisone. This calculator does not cover that use; see the steroid-induced hyperglycemia calculator.
- Pregnancy. NPH has a long safety record in pregnancy and remains a standard option.
NPH Insulin Calculator: Limitations & Safety Notes
- The results are starting estimates for discussion with a prescriber, not a prescription.
- NPH's peak makes meal timing matter. Skipping lunch after a morning dose raises the risk of a low.
- NPH must be mixed before each dose. Roll the pen or vial gently and tip it end to end until the liquid is evenly cloudy; do not shake it hard.
- Never mix NPH with glargine, detemir or degludec in the same syringe.
- Opened NPH has a limited in-use life, from 14 to 42 days depending on the brand and whether it is a pen or vial. Check the package insert.
Frequently Asked Questions: NPH Insulin Dosing
How much NPH insulin should I start with?
A common start is 10 units a day or 0.1 to 0.2 units per kg per day. For an 80 kg adult, that is 8 to 16 units a day. Your prescriber sets the dose and adjusts it every few days from fasting glucose readings.
What is the 2/3 and 1/3 rule for NPH?
When NPH is given twice a day, about two-thirds of the daily total goes before breakfast and one-third in the evening. A 30-unit daily dose becomes 20 units in the morning and 10 units at bedtime.
Should the evening NPH dose be given at dinner or at bedtime?
Bedtime is often preferred. A dinner dose peaks in the middle of the night, when glucose is lowest; a bedtime dose peaks closer to morning, which lowers the risk of overnight lows.
Is Humulin N the same as Novolin N?
Both are human NPH insulin at a concentration of 100 units per mL, made by different companies. Switching between them is usually unit-for-unit, but confirm the change with your prescriber or pharmacist.
How do I convert from Lantus to NPH?
Many protocols give about 80% of the Lantus dose as NPH, split twice daily. For example, 30 units of Lantus becomes 24 units of NPH: 16 units before breakfast and 8 at bedtime. Your prescriber makes the final decision.
Sources
- American Diabetes Association. Standards of Care in Diabetes — 2026. Section 9 (Pharmacologic Approaches to Glycemic Treatment). Diabetes Care. 2026;49(Suppl 1). Link
- Eli Lilly and Company. Humulin N (human insulin isophane suspension) prescribing information. Link
- Sanofi. Lantus (insulin glargine) prescribing information — dose changes when switching from NPH.
- Novo Nordisk. Tresiba (insulin degludec) prescribing information — starting dose for patients already on insulin.
Written by Ryan Mitchell · Last updated: October 2026