Health Tools
Health tool guides for calculators, body metrics, nutrition, hydration, sleep, eye breaks, and everyday wellness checks in the browser.
Articles in Health Tools
- How Our BMI Calculator Works: The Formula, the Cutoffs, and the Edge Cases
Most BMI articles restate the same category table and stop. This one walks through the actual calculator we ship, line by line, including the inputs it rejects, the inputs it answers wrongly, and the design decisions behind them. You will know exactly what the number on screen means and where it sto
- 20-20-20 Rule Timer: What Our Eye Break Tool Does Every 20 Minutes
Most people meet the 20-20-20 rule as advice, follow it for one afternoon, and lose it the first time work gets loud. The rule fails as a memory task because it asks you to notice time while you are focused on something else. Our eye break timer exists because a browser tab can hold the clock so you
- Calorie Calculator: The Mifflin-St Jeor Math Our Tool Runs
A calorie calculator prints four numbers and looks authoritative. The useful question is where each number comes from, because two of the four are pure arithmetic and two depend on a multiplier you pick by feel. Our tool runs the Mifflin-St Jeor equation, and this article walks the exact path from y
- Daily Water Intake Calculator, Explained to the Last Milliliter
Most hydration calculators hide their math behind a label. Ours is three lines of TypeScript in src/components/WaterIntake.tsx, so the honest thing to do is open it up. Here is the exact formula, worked examples with the real rounding behavior, and the inputs the formula deliberately ignores.
- Sleep Cycle Calculator: The Exact Math Behind Your Bedtime
You set the alarm for 07:00, you sleep roughly eight hours, and you wake up groggy anyway. A sleep cycle calculator attacks that problem from one direction. It cannot see your sleep, so it works from the average structure of a night and tells you when to be asleep already. Here is the exact arithmet
- Heart Rate Zone Calculator Math: Both Formulas With Worked Numbers
Enter age 30 with a resting heart rate of 60 into a zone calculator, then delete the resting value and recalculate. On our tool, zone 2 moves from 138 to 151 bpm down to 114 to 133 bpm. Same person, same age, 24 beats of difference, and the tool switches formula without telling you. This article run
- Body Fat Percentage Calculator Guide: The Navy Formulas, Constants, and Failure Modes
We rebuilt our own body fat calculator with a spreadsheet next to the code, and the exercise found one discrepancy worth publishing, one edge case that mislabels a lean person, and one input that breaks the display. This guide walks the actual formulas, then the failure modes, so you know precisely
- Pregnancy Due Date Calculator: How Our Week Tracker Computes Every Number
Most pregnancy calculators show you a date and hide the arithmetic. This article opens our own component and shows every computation, including the inputs it refuses and the one thing it does not ask for. You will be able to reproduce every number on screen with a calendar.
- Macro Calculator Split Ratio: The Fixed 30/45/25 Behind Your Grams
Our macro calculator returns three calorie figures, three macro gram targets, and one water line. Most articles explain what macros are. This one documents the arithmetic our component runs, including one place where our own page copy and our code disagree, and one label in the result chart that rea
