The formula
The calculator runs two equations against the body weight you enter and a single boolean for whether you want a loading phase.
Loading phase (optional, 5–7 days):
Loading dose (g/day) = bodyweight (kg) × 0.3
Per-dose serving (g) = loading dose ÷ 4
Duration = 5 to 7 days
Maintenance phase (always):
Maintenance dose (g/day) = bodyweight (kg) × 0.03, clamped to 3–5 g
Worked example, 80 kg adult, loading enabled:
- Loading: 80 × 0.3 = 24 g/day, split into 6 g × 4 doses for 5–7 days.
- Maintenance: 80 × 0.03 = 2.4 g, clamped up to the 3 g/day floor.
- Saturation: ~1 week with the load, ~3–4 weeks without it.
The 3-gram floor on maintenance is a deliberate clamp; body-weight scaling alone would produce 1.5 g/day for a 50 kg person, which is below what the literature treats as a saturating maintenance dose. The 5-gram ceiling reflects diminishing returns: muscle creatine stores have a finite cap, and excess oral creatine is excreted in urine as creatinine. The calculator never recommends more than 5 g/day for maintenance regardless of body weight.
Why those specific numbers
The 0.3 g/kg loading number and the 0.03 g/kg maintenance number both trace back to the International Society of Sports Nutrition position stand on creatine (Kreider et al., 2017, JISSN), the authoritative reference document for creatine dosing in healthy adults. The position stand consolidates roughly 30 years of supplementation studies into a single dosing framework: load fast at 0.3 g/kg/day across four daily doses for 5–7 days to saturate intramuscular phosphocreatine, then drop to 0.03 g/kg/day (typically clamped to 3–5 g/day) to maintain that saturation indefinitely.
The performance evidence sits underneath this. A 53-trial meta-analysis of randomized controlled trials of creatine supplementation across 1,138 participants found a statistically significant effect on upper-body strength performance, with the effect independent of total dose, duration, or whether a loading protocol was used (Lanhers et al., 2017, Sports Med, PMID 27328852). That last finding is the basis for the calculator's "skip loading" toggle: a flat 3–5 g/day reaches the same saturation point in roughly 3–4 weeks instead of 5–7 days, with the same end-state performance benefit. Loading is faster, not stronger.
Assumptions and limits
The calculator assumes creatine monohydrate. Alternative forms (creatine HCl, ethyl ester, buffered "Kre-Alkalyn", magnesium chelate) do not have comparable evidence bases, and the head-to-head trials that exist do not show them outperforming monohydrate at equivalent doses. If you are using a non-monohydrate form, the gram numbers from this calculator are not transferable without independent dose-response evidence for that specific salt or analog.
The calculator also assumes healthy kidneys and adult body composition. Creatine is excreted as creatinine, and elevated serum creatinine on a lab panel is the standard surrogate for reduced glomerular filtration. People with chronic kidney disease, a single kidney, or active nephrotoxic medication exposure should not use this calculator's outputs without prescriber review. The reason is not that creatine has been shown to damage healthy kidneys (it has not, across multiple long-term trials), but that the math assumes excretion capacity that may not be present.
Two edge cases the calculator does not model:
- Vegetarian baseline depletion. Vegetarians and vegans typically have lower baseline intramuscular creatine and tend to respond more strongly to supplementation. The dose is the same; the magnitude of response is not.
- Extreme body-fat-percentage skew. The 0.03 g/kg maintenance scales by total body weight, not lean mass. At very high body-fat percentages, lean mass is over-estimated by total weight, and the 5 g/day clamp is what prevents over-dosing in that regime.
Unit conventions
Everything is in grams, not milligrams or micrograms. A 5 g maintenance dose is approximately one rounded teaspoon of creatine monohydrate powder (density varies slightly by brand). Doses are per day, not per meal. Within a day, timing matters less than total intake. The position stand notes a small post-workout-with-carbs advantage but treats it as secondary to consistent daily dosing.
Hydration matters. Creatine is osmotically active and pulls water into muscle cells, which is part of why scale weight rises 1–2 kg in the first week of loading. Drink to thirst plus an extra ~500 mL/day during the loading phase. The calculator does not model fluid balance, but the ISSN position stand explicitly recommends adequate water intake during supplementation.
Why this is documentary, not prescriptive
This calculator and the page that hosts it are documentary. They show you what the ISSN position stand prescribes, scaled to your body weight, with the math made visible. They are not a prescription, and they do not know anything about you that you have not typed in.
If you have chronic kidney disease, are on diuretics or other nephrotoxic medications, are pregnant or breastfeeding, or are under 18, the outputs of this calculator need a prescriber review before they apply to you. If your goal is medical (treating a diagnosed creatine-deficiency syndrome, supporting recovery from a specific neurological or muscular condition), the dosing in this calculator is for healthy-adult performance supplementation and does not transfer to those clinical contexts.
The PMID cited above was verified live against PubMed by the same INT-01 citation guardrail that gates the calculators on this site. We do not write a citation we have not fetched.