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BMI Calculator — body mass index with history
Calculate your **BMI** (body mass index) from weight and height and keep a history of every measurement over time: enter the numbers once and the result shows up right in the table, no manual math required. As always with Reactive, everything stays on your own device.
What it records
- Weight in kg
- Height in meters, e.g. 1.75 (not centimeters)
How it works
This is a Reactive app: a plain text document that your browser turns into a working app — forms, live data, tables, statistics and even charts, with nothing to install or configure.
- Use it right away. Hit “Use this app”: it opens right in your browser, ready to go, with data saved only on your device.
- Your data stays yours. Everything is stored locally on your device, kept separate for each app: no account, no server, nothing to set up.
- Make it your own. The text below is the entire app: copy it, tweak fields, views and words, and your changes become interactive instantly.
- Share it as a file. An app is a simple file: save it, export it or share it with a link; and with encrypted collaboration several people edit the same data in real time.
The app’s source
# ⚖️ BMI Calculator
Calculate your **BMI** (body mass index) from weight and height and keep a
history of every measurement over time: enter the numbers once and the
result shows up right in the table, no manual math required. As always with
Reactive, everything stays on your own device.
::::form{path="measurements" id="fbmi"}
::input{form="fbmi" field="date" type="date" legend="When"}
::input{form="fbmi" field="weight" type="number" placeholder="Weight in kg" required="true"}
::input{form="fbmi" field="height" type="number" placeholder="Height in meters, e.g. 1.75 (not centimeters)" required="true"}
::add-form{form="fbmi" path="measurements" label="Calculate BMI"}
::::
:::table{path="measurements" headers="Date,Weight (kg),Height (m),BMI" deletable="true" editform="fbmi"}
{date} | {weight} | {height} | {weight/height/height}
:::
**How to read your BMI:**
- Underweight: below 18.5
- Normal weight: 18.5 – 25
- Overweight: 25 – 30
- Obesity: above 30
Height must be entered **in meters** (e.g. "1.75"), not centimeters — the
most common mistake when calculating BMI by hand. The value in the table
updates automatically as soon as you edit a row's weight or height.