A two-formula calculator dressed up as a health app.

The app is two calculators and a reference chart. Enter height, weight, age, sex, and an activity multiplier; it returns a Body Mass Index value with its WHO band (underweight, normal, overweight, obese class I-III) and a Basal Metabolic Rate estimate using the Mifflin-St Jeor equation. Multiply BMR by an activity factor and it gives you a Total Daily Energy Expenditure — the rough calorie number most fitness apps anchor to.

Beyond that, there isn't much. A static chart of BMI ranges, a small explainer screen, and units that toggle between metric and imperial. No history, no profile, no sync, no integration with Fitbit or Health Connect, no graphs of inputs over time. Open it, type, read, close.

That minimalism is the entire pitch. It loads in under a second on a 2018 Fire HD 10, takes about 4 MB on disk, and asks for zero permissions.

Doing one thing without nagging counts for something. The app doesn't pester for an account, doesn't push notifications, doesn't gate the BMR calculation behind a subscription, and doesn't try to sell you a 12-week meal plan on the way out. For a free Amazon Appstore utility in a category infested with subscription traps, that restraint is the differentiator.

The math also appears to be correct. Spot-checking Mifflin-St Jeor against the published formula matches to one decimal, and the BMI bands line up with the WHO thresholds. That sounds like a low bar; spend ten minutes in this category and you'll find apps that get either one wrong.

The bigger issue isn't the app — it's BMI itself. The metric was designed in the 1830s to describe populations, not individuals, and it ignores body composition entirely. A muscular adult lands in "overweight" and a sedentary one with the same number lands in "normal." Major medical bodies including the American Medical Association have publicly questioned its clinical usefulness for individuals since 2023. A serious health app would at least surface that caveat alongside the result. This one doesn't.

The BMR number has a softer but real version of the same problem — Mifflin-St Jeor is a population average with a roughly 10% error band for any given person. Treating its output as a literal calorie target, which the app's framing invites, will mislead a non-trivial share of users by 200-400 kcal a day.

Cosmetically, the Fire-tablet layout wastes the screen on tablets, the chart graphic looks lifted from a 2014 Android tutorial, and there's no way to save a result to compare next month.

As a free Fire-tablet calculator, this is fine. As a tool that meaningfully informs a decision about your health, it isn't — and that's mostly the fault of the metrics it computes, not the developer. Use it the way you'd use a tip calculator: get the number, take it as one data point, don't reorganise your life around it. If you want something that does take body composition seriously, a smart scale paired with its own app does more useful work for not much more money.