NMN Dosage by Body Weight (mg/kg): Why the Math Is Wrong

Search for "NMN dosage by body weight" and you'll find calculators promising a personalized milligrams-per-kilogram number — take your weight, multiply by some per-kg figure, and out comes "your" dose. It feels rigorous and scientific. It is, unfortunately, built on a basic error: those per-kg numbers are reverse-engineered from mouse studies, and they cannot be honestly scaled to a human body by simple multiplication. The actual human NMN trials never dosed by weight at all — they used flat doses, almost always in the 250–1,250 mg/day range, regardless of how much the participant weighed.

This page explains where the mg/kg numbers come from, why the mouse-to-human conversion that underlies them is wrong, and what the real human dose-finding studies actually used — so you can ignore the weight-based calculators with confidence.

Where the "mg/kg" numbers actually come from

The per-kilogram figures floating around supplement forums trace back to the famous mouse longevity work. In the landmark long-term study, mice were given NMN in their drinking water at roughly 100–300 mg/kg/day and showed mitigation of age-related physiological decline ¹. Someone then took that mouse mg/kg number and multiplied it by a human's body weight — for example, "300 mg/kg × 70 kg = 21,000 mg" — and either used it directly or scaled it down by a hand-wavy factor. Both approaches are wrong, because the dose a mouse needs per kilogram is not the dose a human needs per kilogram.

Why mouse-to-human mg/kg doesn't transfer

The reason is metabolic-rate scaling, and it's textbook pharmacology, not a fringe objection. Small animals have a far higher metabolic rate per kilogram of body weight than large animals, so they clear and use drugs faster per kilogram. To convert an animal dose to a human-equivalent dose (HED), pharmacologists don't multiply by body weight — they divide by a species-specific scaling factor based on body-surface area. The standard guide assigns mice a conversion factor of about 12.3, meaning a mouse mg/kg dose must be divided by roughly 12 to estimate the human-equivalent mg/kg, not used as-is ².

Run the real math and the "calculator" doses collapse. A 300 mg/kg mouse dose converts to roughly 24 mg/kg human-equivalent (300 ÷ 12.3) — about 1,700 mg for a 70 kg person, in the same ballpark as the flat doses humans were actually given. The naive "300 mg/kg × your weight" version overshoots by more than ten-fold. So the mg/kg calculators aren't just imprecise; the simple ones are off by an order of magnitude in the dangerous direction. (For practical, evidence-based dosing instead of this flawed arithmetic, see our NAD+ and NMN dosage guide.)

What the human NMN trials actually used: flat doses

Here's the decisive point the calculators ignore: no published human NMN trial dosed participants by body weight. Every one used a fixed flat dose. Walking through them makes the real-world range obvious:

• •A single-dose study in healthy men tested 100, 250, and 500 mg and found even 500 mg was safely metabolized ³.
• •The widely cited metabolic trial gave prediabetic women 250 mg/day ⁴.
• •Studies in older adults used 250 mg/day for 12 weeks and reported elevated blood NAD+ with effects on muscle function, walking speed, and sleep ⁵⁶⁷.
• •A randomized dose-finding trial in middle-aged adults compared 300, 600, and 900 mg/day ⁸.
• •A safety study established that a single dose as high as 1,250 mg was well tolerated ⁹.

A 60 kg woman and a 100 kg man in these trials received the same 250 mg — and both raised their blood NAD+. That is the opposite of how a weight-based drug is dosed, and it tells you the field simply does not treat NMN as an mg/kg compound.

Why flat dosing is actually defensible here

This isn't sloppiness on the researchers' part. NMN's measurable effect — raising blood NAD+ — appears to plateau: across these trials, going from 250 mg to higher doses produced diminishing additional increases in NAD+, not a clean dose-proportional climb. When a supplement's biomarker saturates, fine-tuning the milligrams to someone's body weight buys little, which is exactly why the trials standardized on round flat numbers. It's also worth remembering that "raises blood NAD+" is itself a long way from "delivers a health benefit" — NAD+ rises reliably in these studies while functional benefits remain modest and inconsistent — so chasing a precision-dose by weight optimizes a number that may not translate to how you feel anyway. NAD+ does decline with age and metabolic stress ¹⁰, which is the rationale for supplementing at all, but that rationale doesn't resurrect mg/kg dosing.

The honest bottom line on NMN dosing by weight

• •The mg/kg calculators are extrapolated from mouse studies ¹ and rely on a mouse-to-human conversion that is mathematically wrong — animal doses must be scaled down by a surface-area factor (÷~12 for mice), not multiplied by your weight ².
• •No human NMN trial dosed by body weight. They used flat doses, overwhelmingly 250 mg/day, up to single doses of 1,250 mg ^3456789.
• •Because NMN's NAD+ effect plateaus, body-weight precision buys little — and the felt benefit of raising NAD+ is itself uncertain.

If you're choosing a dose, ignore the per-kg calculators and anchor to what was actually studied in people: most evidence sits at 250 mg/day, with safety demonstrated well above that. For a fuller breakdown, see our NAD+ and NMN dosage guide; to pick a product at a sensible dose and verified purity, see our best NMN supplements rankings and the absorption question in sublingual NMN vs capsules. And for the broader question of whether any of this delivers, start with our NAD+ therapy evidence pillar and the NAD+ rankings hub.