Health Tools

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Thirty-two calculators, every formula named

Body fat from a tape measure, ideal weight by four formulas that disagree by ten kilograms, five ways to compute a body surface area, heart rate zones by Karvonen or by percentage, a one-rep max with the plates to load, a paediatric dose turned into millilitres of the syrup on the label, an eGFR with the stage underneath, blood pressure named by whichever guideline you pick, a glucose column converted into all four units it is printed in, and a calendar for a cycle, a course of tablets or a streak.

Every one of these is arithmetic and none of it is advice, and that is built into the shape of the thing rather than written at the bottom. Where several published formulas exist they are all shown, because presenting one as the answer would be inventing a precision nobody has. Where a number means something only against a boundary, the whole ladder is drawn with your value marked on it — "overweight" on its own is a judgement handed down; the same word with the four other bands and their boundaries beside it is a measurement you can check.

The clinical tools decide nothing. The dosage calculator converts the milligrams per kilogram somebody else prescribed; the insulin tool applies the ratios a diabetologist set; the eGFR tool runs a published equation on a laboratory value. None of them holds a drug database, none suggests a parameter, and each shows its working so that the arithmetic can be checked rather than trusted. Everything runs inside this browser tab, which for these tools is not a feature but the precondition: a cycle tracker, a sobriety counter and a blood pressure log are among the most sensitive things a person owns.

Body

Body fat
Body fat from a tape measure, by the US Navy method.

Ideal weight
Four published formulas that disagree by ten kilograms.

Waist to hip
Waist to hip and waist to height, with both ladders drawn.

Lean body mass
Three formulas, or the exact figure from a measured body fat.

Child height
Mid-parental height, and the eight and a half centimetres either side.

Fitness

VO₂ max
Three field tests, and where the result sits for your age.

One-rep max
Four formulas, the whole percentage table and the plates to load.

Clinical

IV drip rate
Drops a minute and the pump rate, with the working shown.

eGFR
Four published equations, and the stage they put a result in.

Blood pressure
The same reading, named by the American guideline and by the European one.

Insulin dose
A meal dose and a correction dose, from ratios somebody else set.

Readings

Glucose units
A column of readings in all four units they are printed in.

Habits

Smoking cost
What the habit costs over twenty years, invested or not.

Sober days
A streak in days, weeks and calendar words, with the milestones.

Blood alcohol
Widmark's estimate, and the range that must never decide a drive.

Age
An age said the four ways people say it, and the next birthday.

Daily

Daily water
A range from body mass, exercise and heat — not eight glasses.

Sleep cycles
What time to go to bed, counted in whole cycles.

Sun exposure
Time to a burn by skin type, and what a bottle really buys.

Cycle calendar
Next periods and the fertile window — a projection, not contraception.

Vaccination dates
Your card's intervals turned into dates. No national schedule is shipped.

Questions

Is any of this medical advice?
No, and every result here says so on its own face. These tools do arithmetic on numbers you supply, with the formula named. Nothing here diagnoses anything, nothing prescribes anything, and no result should change what you do without a clinician in the conversation.
Why do two calculators give me different answers for the same thing?
Because the published formulas genuinely disagree. Maximum heart rate by age has at least four estimates that differ by twenty beats and each has a standard error of about twelve; ideal weight has four that differ by ten kilograms; body surface area has five. Every tool here shows all of them and says which one produced the headline number.
Is my health data uploaded anywhere?
No. The tools are compiled to WebAssembly and run inside the browser tab. Nothing you type is sent to a server, nothing is stored except the settings you last used, and you can watch your browser's network panel while you use one to see that nothing leaves the page.
Does the vaccination tool know my country's schedule?
No, and deliberately. There are as many national schedules as there are countries, they differ in which vaccines at what ages, and they are revised — a table baked into a web page would be wrong somewhere on the day it shipped. You type the intervals off the card and it turns them into dates.