Supplement Dosage Calculator
Select a supplement and enter your bodyweight to get an evidence-based personalised dosage recommendation.
Quick Answer
Evidence-based supplement dosages by bodyweight: Creatine monohydrate 0.075g/kg/day (max 5g). Caffeine pre-workout 3–6mg/kg. Magnesium glycinate 4–5mg/kg/day (max 400mg). Vitamin D and omega-3 dosages are not strongly weight-dependent — standard doses of 1,000–2,000 IU and 1,000mg EPA+DHA respectively are appropriate for most adults.
Why Supplement Dosage Matters
Taking too little of a supplement produces no benefit. Taking too much risks side effects, wasted money, and in some cases genuine health risks. For many supplements, the effective dose is weight-dependent — a 100 kg athlete needs considerably more creatine than a 55 kg person to achieve the same intramuscular saturation.
Our calculator provides personalised, weight-based dosing for the supplements with the strongest evidence base. Every recommendation includes the source organisation or study behind it — so you can verify the evidence yourself.
The Most Researched Supplements
Creatine monohydrate is the most extensively researched sports supplement in history with over 500 studies supporting its safety and efficacy. It increases phosphocreatine stores in muscle, directly improving ATP regeneration during high-intensity exercise. Benefits are consistent across strength training, sprinting, and team sports. Effects are particularly pronounced in vegetarians and vegans who have low dietary creatine intake.
Caffeine has a strong evidence base for improving endurance performance, strength, and cognitive function. At 3–6mg/kg bodyweight, it reliably reduces perceived exertion and increases time to fatigue. Tolerance develops rapidly — cycling off caffeine for 2 weeks every 2 months maintains sensitivity. The effective dose is meaningfully weight-dependent, which is why calculating it per kilogram matters.
Vitamin D functions more as a hormone than a vitamin. It regulates calcium absorption, immune function, mood, and muscle function. Deficiency is associated with depression, reduced immune function, muscle weakness, and impaired recovery. Standard supplementation of 1,000–2,000 IU/day is appropriate for maintenance; those with confirmed deficiency may need 4,000–5,000 IU under medical supervision until levels normalise.
Magnesium is involved in over 300 enzymatic reactions including muscle contraction, protein synthesis, and nerve transmission. Dietary insufficiency is widespread — intensive agricultural practices have reduced soil magnesium content, and processed foods are low in magnesium. Glycinate and malate forms have better bioavailability than oxide. Evening dosing may improve sleep quality.
What Most Supplements Are Not
The supplement industry is largely unregulated and full of products with minimal evidence. Most pre-workout formulas contain effective ingredients (caffeine, creatine, beta-alanine) in sub-effective doses alongside proprietary blends of unproven ingredients. Fat burners, testosterone boosters, and most "recovery" products have weak to nonexistent evidence. The core stack — creatine, protein (if needed), vitamin D, omega-3, magnesium — covers the vast majority of what the evidence supports for most people.
Medical Note
Consult a pharmacist or doctor before supplementing if you take prescription medications. Some supplements interact with drugs (e.g. high-dose omega-3s with blood thinners, magnesium with some antibiotics). These are general guidelines — individual needs vary.