Health numbers, honestly explained
Five free calculators that give you the number and then tell you what it can’t see. No signup, nothing stored, sources on every page.
What we do differently
The number comes with its limits
Every tool says what it cannot tell you. BMI cannot see body composition; calorie equations carry a 10–20% error; sleep cycles vary night to night. Those caveats sit next to the result, not buried at the bottom.
Nothing leaves your browser
Calculations run locally in JavaScript. No accounts, no health-data collection, nothing transmitted. Verifiable in your browser's own developer tools.
Sources you can check
Each page links its primary sources — WHO, CDC, the National Academies, peer-reviewed equations — so you can read past our summary of them.
Start where it's useful
If you are trying to understand a single number you have been given, start with BMI — it is the most commonly quoted and the most commonly misread. If you are planning changes to how you eat, calories and TDEE gives you the baseline to work from. If you wake up tired despite enough hours in bed, sleep cycles may explain why. And if you have a family history of dementia or stroke on your mind, the brain health score covers the twelve factors that carry the most evidence.
Questions
Are these calculators accurate?
They use the same published equations clinicians use — Mifflin-St Jeor for calories, the WHO formula for BMI — but every population-level equation carries an individual margin of error, typically 10 to 20%. Each page states its own limits rather than presenting a number as fact.
Do you store my height, weight or any health data?
No. Every calculation runs in your browser and nothing is sent anywhere. There are no accounts and no health data collection. You can confirm it yourself: open your browser's Network tab and watch that nothing leaves the page while you use a calculator.
Is this medical advice?
No. These are informational tools for generally healthy adults. Pregnancy, chronic conditions and medications all change what the numbers mean, and a clinician has better instruments than a formula. Anything that matters is worth discussing with one.
VitalTally is an independent site. We sell nothing, collect no health data, and have no commercial relationship with any health provider or product. Tools are informational and are not medical advice.