CitedDose
Evidence-based supplement calculators. Every number traces to a cited trial or guideline, and every page is reviewed by a licensed professional.
Supplement advice online is mostly marketing. These calculators do one thing each, show the number, and link the systematic reviews and position stands the number comes from. Nothing here is medical advice; it is the published evidence, organised so you can read it in two minutes.
Collagen Dosage Calculator: How Much Collagen Per Day for Skin, Joints and Bones (2026 Evidence)
How many grams of hydrolyzed collagen per day for skin, joints, bone density or muscle, based on the doses used in randomized trials, with how long until you should expect results.
Protein Intake Calculator: Grams Per Day by Weight, Goal and Age (ISSN and RDA Based)
Calculate grams of protein per day from body weight, activity and goal, using the RDA (0.8 g/kg), the ISSN position stand (1.4 to 2.0 g/kg for training) and higher ranges for fat loss and older adults.
Creatine Dosage Calculator: Loading Phase vs 3 to 5 g Daily, by Body Weight (ISSN)
Work out your creatine monohydrate dose: optional loading phase at 0.3 g/kg for 5 to 7 days, or a steady 3 to 5 g a day, with time to saturation and water-weight expectations.
Vitamin D Dosage Calculator: IU Per Day by Age, Weight, Sun Exposure and Blood Level
Estimate a daily vitamin D3 dose from age, body weight, sun exposure and, if you have one, your 25(OH)D blood level, using the IOM RDA, the 4,000 IU upper limit and the 2024 Endocrine Society guideline.
Supplement Interaction Checker: Which Vitamins, Minerals and Herbs Not to Take Together or With Medications
Tick the supplements and medication types you take to see documented interactions, absorption conflicts and timing fixes, drawn from NIH Office of Dietary Supplements and clinical pharmacology references.
Guides and evidence reviews
Does collagen work for skin? What the 2026 meta-analysis found
A plain-language reading of the 2026 meta-analysis of collagen peptide trials: real gains in hydration and elasticity, no reliable effect on wrinkles, and why trial funding matters.
Vitamin D: the 2024 Endocrine Society guideline in plain language
Who should take vitamin D beyond the recommended daily amount, who should not, and why routine blood testing is no longer advised, according to the 2024 Endocrine Society guideline.
How much protein per meal?
The evidence on protein per meal: the 0.4 g/kg guideline, why the old 20 to 30 g ceiling was too simple, what the 2023 100 g study found, and a per-meal table by body weight.
Creatine loading vs daily dosing
Do you need a creatine loading phase? The 1996 study that answered it, how long each method takes to saturate muscle, the side effects of loading, and who should actually load.
Protein needs over 60: why the RDA is too low
Two expert groups recommend 1.0 to 1.2 g of protein per kg a day for healthy older adults, more when ill, with 25 to 30 g per meal. What the evidence says, a table by body weight, and how to actually eat it.
Vitamin D dose by body weight
A 17,614-person study found the same vitamin D dose raises blood levels far less in heavier people, and that overweight adults need about 1.5 times and obese adults 2 to 3 times the dose. How to size a daily dose by weight, and where the 4,000 IU ceiling fits.