How VitalTally Works
Every formula, every threshold, every source — and the things we deliberately do not claim.
What we are, precisely
VitalTally aggregates published health guidance and standard formulas into free calculators and plain-language articles. That is the entire claim. We are not clinicians, we do not employ clinicians, and we do not review your individual situation.
Our articles carry an organisational byline rather than an invented expert name, because inventing one would be dishonest and naming a real clinician who has not reviewed the page would be worse. What we offer instead is checkability: every health claim on this site is tied to a public document from a health authority, and you can read that document yourself.
Medical disclaimer: Nothing on VitalTally is medical advice, diagnosis, or treatment. Calculator outputs are population-level estimates, not statements about you. Talk to a qualified clinician about anything that matters to your health, and never change a medication or treatment on the basis of a web calculator.
The formulas
BMI
Body Mass Index is weight in kilograms divided by height in metres squared. In imperial units: weight in pounds × 703, divided by height in inches squared. Categories follow the CDC's current adult classification: under 18.5 underweight, 18.5 to less than 25 healthy weight, 25 to less than 30 overweight, 30 and above obesity.
What BMI does not do: it does not distinguish muscle from fat, does not account for where fat is stored, and its thresholds are not equally appropriate for older adults, children, or every ethnic background. It is a screening measure, not a diagnosis.
Calories
Resting metabolic rate uses the Mifflin–St Jeor equation: for men, (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5; for women, the same with −161 instead of +5. Total daily energy expenditure multiplies that by a standard activity factor from 1.2 (sedentary) to 1.9 (extra active).
What it does not do: the activity multipliers are broad brackets, individual metabolism varies substantially around the equation, and a calorie deficit does not produce weight loss in a straight line — the body adapts. Treat the number as a starting estimate to adjust from, not a prescription.
Hydration
The reference figures are the National Academies' Dietary Reference Intakes for total water: approximately 3.7 litres (125 oz) a day for men and 2.7 litres (91 oz) for women, from all beverages and foods combined — roughly 20% of it comes from food.
An important caveat about this tool. The National Academies deliberately decline to set an individual daily requirement, and specifically do not endorse any rule of thumb about glasses of water per day: "the vast majority of healthy people adequately meet their daily hydration needs by letting thirst be their guide." Our calculator adjusts the population reference for body weight, activity and climate to give you a rough personal figure — but thirst remains the better guide, and the brackets we use are our own simplification, not a published standard.
Sleep
Recommended sleep durations by age come directly from the CDC. Bedtime suggestions assume sleep cycles of about 90 minutes plus roughly 15 minutes to fall asleep.
What it does not do: 90 minutes is a population average. Real cycles run roughly 70 to 120 minutes and lengthen through the night, so cycle-timed wake times are approximate. No health authority endorses cycle-timing calculators as a clinical tool.
Brain Health Score
An adaptation of the Brain Care Score developed by the McCance Center for Brain Health at Massachusetts General Hospital: twelve questions across physical health (8 points), lifestyle (9 points) and social-emotional factors (4 points), for 21 points total.
What it does not do: this is our adaptation, not the validated clinical instrument, and VitalTally is not affiliated with Mass General. It does not predict what will happen to you. Its value is in showing you which of twelve modifiable factors is most worth raising with a clinician.
Where our numbers come from
We cite the agency that publishes the guidance, not a site summarising it. Our standing sources:
- Centers for Disease Control and Prevention — blood pressure and A1C classifications, BMI categories, sleep duration by age, physical activity guidelines. cdc.gov
- National Institutes of Health, particularly the National Institute on Aging and NHLBI — dementia risk research, sleep and cardiovascular health, DASH. nih.gov
- National Academies of Sciences, Engineering, and Medicine — Dietary Reference Intakes for water. nationalacademies.org
- Alzheimer's Association — dementia prevention and risk. alz.org
- Dietary Guidelines for Americans (USDA / HHS) — eating patterns. dietaryguidelines.gov
- World Health Organization — alcohol and health. who.int
How we handle "this reduces your risk"
Almost all brain-health evidence is observational: researchers watch large populations and find that people who do X have less of Y. That is not the same as showing that doing X causes less Y, and the difference matters enormously to what you should expect from a habit change.
So we write "is associated with" when the evidence is observational, and reserve "reduces" for findings from randomised trials. Where a famous trial came out negative — SPRINT MIND on dementia, the 2023 MIND diet trial, ACHIEVE on hearing aids in the overall population — we say so on the page rather than quoting only the encouraging observational result. Several of those caveats were added on 8 September 2026, when we audited every claim on this site against its source.
Corrections
If a figure here is wrong, a threshold is out of date, or we have cited a source for something it does not actually say, tell us through the contact page and name the page and the sentence. We check it against the primary source, fix it, and note the correction rather than quietly editing.
Corrections log
- 8 Sep 2026 — Sleep calculator: the recommended-hours table was replaced with the CDC's current figures. Four age bands were wrong (infants, school age, teens, adults) and the preschool band was missing entirely.
- 8 Sep 2026 — BMI calculator: category labels updated to the CDC's current wording ("healthy weight", "obesity") and the healthy band restated as 18.5 to less than 25.
- 8 Sep 2026 — Brain Health Score: specific percentage risk-reduction figures were removed. We could not re-verify them against the source papers, and an unverifiable precise number is worse than an honest qualitative statement. The twelve questions are now also rendered as readable text on the page.
- 8 Sep 2026 — Blood pressure and dementia articles: "the single most important modifiable risk factor" corrected to "one of the most important". It was not supportable, and it contradicted another page on this site.
- 8 Sep 2026 — Several causal phrasings changed to associative ("lowers future risk" → "is associated with lower future risk"; "protective tools" → "interventions"), and treatment-target language ("is the goal", "is the target") changed to the CDC's classification language.
- 8 Sep 2026 — Byline changed from "Reviewed against published research" to a plain statement that sources are listed on the page. The old wording asserted a review process without naming a reviewer.
What we do not do
We do not collect your health inputs. Every calculator runs in your browser; the numbers you enter never reach our servers.
We do not sell anything, and we do not recommend products. The site is funded by advertising. Ads never influence which guidance we cite or what an article concludes.
We do not diagnose. If a result here worries you, that is a reason to talk to a clinician, not a reason to act on the number.
Last reviewed: 8 September 2026.