Free Health & Fitness Calculators

BMI, calorie counting, macro tracking and ideal weight calculators. Your data stays in your browser.

🔍

How to Use These Health Calculators Together

Each calculator answers a different question, and they work best as a sequence. Start with the BMI Calculator to screen where you stand: BMI compares your weight to your height (kg/m²) and maps to WHO categories — under 18.5 is underweight, 18.5–24.9 is normal, 25–29.9 is overweight, and 30+ is obese. BMI is a population-level screening tool, not a diagnosis: muscular athletes often score "overweight" despite low body fat, which is why the Body Fat Calculator (US Navy tape-measure method) gives a more relevant picture of body composition.

Next, the Calorie Calculator estimates your TDEE (Total Daily Energy Expenditure) from your basal metabolic rate and activity level. Eat below TDEE to lose weight, at TDEE to maintain, or above it to gain. The Macro Calculator then splits those calories into protein, carbohydrate, and fat — useful because a gram of protein and a gram of carbohydrate each carry about 4 kcal, while a gram of fat carries about 9 kcal. Common starting points are protein in the range of 1.2–2.2 g per kg of body weight with the remainder split between carbs and fat depending on training volume and preference.

The remaining tools cover specific situations: the Ideal Weight Calculator shows how much healthy ranges differ between classic formulas (Devine, Robinson, Miller, Hamwi) — they can disagree by several kilograms, so treat the overlap as the realistic target zone. The Sleep Calculator plans bedtimes around 90-minute sleep cycles so you wake between cycles rather than mid-cycle. The Alcohol Burning Time Calculator uses the Widmark formula to estimate how long alcohol remains in your system. All calculations run locally in your browser — no data is uploaded.

Health Calculator FAQ

Is BMI accurate for athletes and older adults?
BMI can be misleading at the individual level. It does not distinguish muscle from fat, so muscular athletes frequently land in the "overweight" range despite healthy body composition. In older adults, BMI can understate fat mass because height shrinks with age. Use BMI as a quick screen and pair it with body fat percentage or waist measurement for a more complete picture.
What is TDEE and how is it calculated?
TDEE (Total Daily Energy Expenditure) is the total number of calories you burn per day, including your basal metabolic rate (BMR — energy used at complete rest, typically 60–70% of TDEE), the thermic effect of food, and physical activity. Calculators estimate BMR with formulas such as Mifflin-St Jeor, then multiply by an activity factor from 1.2 (sedentary) to about 1.9 (very active).
What macro split should I use to lose weight?
Weight loss fundamentally depends on a calorie deficit; the macro split is about satiety, muscle retention, and performance. A practical starting point: set protein first (roughly 1.6–2.2 g/kg for people who train), keep fat at least 20–25% of calories for hormonal health, and fill the rest with carbohydrates. Higher-protein splits tend to preserve lean mass and reduce hunger during a deficit.
Why do ideal weight formulas give different results?
The classic formulas (Devine 1974, Robinson 1983, Miller 1983, Hamwi 1964) were each derived from different datasets and for different clinical purposes — Devine, for example, was designed for drug dosing. They can differ by 5+ kg for the same person. Rather than treating any single number as a target, check which weight range multiple formulas agree on, and combine it with body composition and how you feel.
How does the sleep calculator's 90-minute cycle work?
Sleep occurs in repeating cycles of roughly 90 minutes (light sleep → deep sleep → REM). Waking during deep sleep causes grogginess (sleep inertia); waking between cycles feels easier. The calculator counts back 90-minute blocks from your wake time — typically recommending 5–6 cycles (7.5–9 hours) for adults — and adds ~15 minutes of average time to fall asleep.
How long does alcohol stay in your system?
The body metabolizes roughly one standard drink per hour on average, but the exact rate depends on body weight, sex, food intake, and individual metabolism. The Widmark formula estimates blood alcohol concentration from the amount consumed, your weight, and a sex-specific distribution constant. The only reliable way to sober up is time — coffee, showers, and food do not accelerate metabolism. Never drink and drive.