BMI tracker diary: log weight and see BMI with cited sources
Free printable weight loss tracker (PDF)
A BMI tracker diary is a weight log that also shows body mass index as a calculated number. Blood Snap stores the kilograms or pounds you confirm, uses the height on your profile, and shows BMI with the formula and the public sources beside it. The number is there so you can read it and discuss it. It is not a diagnosis.
Blood Snap is a personal wellness diary, not a scale and not a medical device. You weigh yourself. The app does the arithmetic and cites the World Health Organization and the U.S. Centers for Disease Control and Prevention.
The BMI formula Blood Snap uses
The adult formula, as published by the WHO healthy-lifestyle fact sheet and the CDC Adult BMI categories page, is:
BMI = weight (kg) / [height (m)]²
An arithmetic example, the same one shown in Blood Snap logging tips: 72 kg and 1.70 m gives 72 / (1.70 × 1.70) = 24.9. That example teaches the formula. It is not a goal and not a result the app assigns to you.
If you log pounds, Blood Snap converts to kilograms before it divides. Height is stored in centimetres and converted to metres. You can set height during setup or later in your profile. The line under the number reads as a source line: WHO and CDC.
Adult BMI categories, cited as education
The CDC publishes adult BMI categories, and the WHO discusses the same broad adult cut-points in its healthy-lifestyle education. Blood Snap links those pages. It does not stamp a category onto your diary, and it does not diagnose underweight, overweight, or obesity.
| Adult BMI | Category name on the CDC page |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25.0 to 29.9 | Overweight |
| 30.0 and above | Obesity |
Those names are the CDC's published labels for adult BMI ranges, also reflected in WHO adult education. They describe a calculation for populations. They do not describe your muscle, age, pregnancy, medicines, or medical history. Blood Snap will not apply them as a badge on your Home screen. If a clinician uses BMI, they use it with the rest of your record.
How the diary shows BMI
- Save your height in centimetres on your profile.
- Open More Health → Weight and log the scale in kg or lb. Type it, or snap or speak a clear scale display and confirm every digit.
- Read the BMI number next to the WHO and CDC links. The links stay visible with the number.
- Optional: turn on the weight card under Show on dashboard if you want it on Home.
- Open Analytics for a 3-day, 7-day, or 30-day view of the weights you logged.
For the scale habit without the formula, see how the weight log works. To keep the cuff in the same diary, see the weight and blood pressure log.
What a BMI diary is good for
- A repeatable weight record in one unit, with dates.
- A calculated BMI you can read beside the cited formula.
- A trend over 3, 7, or 30 days, which is steadier than one morning on the scale.
- A Pro PDF or CSV when a clinic asks for the weights you entered.
Daily swings of a kilogram are common and often reflect food, fluid, and clothing. The diary is more useful when you weigh at a similar time, on the same scale, and look at the week.
What this diary cannot do
- It does not diagnose obesity, overweight, or underweight.
- It does not measure body fat, fitness, or health.
- It does not replace WHO or CDC pages, and it does not replace your clinician.
- It does not count calories or prescribe a diet.
- It does not connect to a Bluetooth scale. You confirm the number from the display you photographed or typed.
Log weight and read BMI with the sources in view. Blood Snap calculates BMI from height and the weight you confirm, and cites the WHO and CDC. The number is educational. Free weight logging, Pro export. Not a medical device and not a diagnosis.
Educational information with public guideline citations. Not medical advice and not a diagnosis. Blood Snap is a personal wellness diary — not a medical device, blood pressure machine, glucometer, or CGM. Always follow your clinician's advice.