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Health & Fitness
Calculators —
20+ Free Tools

BMI, calories, macros, pregnancy, sleep, running pace, body fat, water intake and more. Built on proven medical formulas — Mifflin-St Jeor, Harris-Benedict, WHO standards. Instant results, no registration.

20+
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Body Nutrition Women’s Health Fitness Sleep FAQ
🟢 Body & Weight
Body Composition Calculators
04
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BMI Calculator
Calculate Body Mass Index — underweight, healthy, overweight or obese range using WHO standards.
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BMR Calculator
Basal Metabolic Rate — calories your body burns at rest using Mifflin-St Jeor formula.
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Body Fat Percentage Calculator
Estimate body fat using Navy method, BMI or skinfold formulas. Track progress accurately.
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Body Shape Calculator
Determine your body shape — apple, pear, hourglass, rectangle or inverted triangle.
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How It Works
1
Choose Your Category
Use the sticky nav above to jump to Body, Nutrition, Women’s Health, Fitness or Sleep. Or start with the BMI Calculator — it feeds directly into most other tools.
2
Enter Your Details
Each tool asks for only what it needs — typically age, height, weight and activity level. No account, no email, no personal data stored.
3
Get Instant Results
Results appear immediately using validated scientific formulas. The Calorie Calculator uses Mifflin-St Jeor. The BMR Calculator supports both Mifflin-St Jeor and Harris-Benedict.
4
Track Your Progress
Screenshot or save your results. Return as your stats change — all calculators update instantly and are completely free to use as many times as you need.
Why Use Sitnit Health Tools
🏛️
Science-Based Formulas
Every tool uses validated medical and fitness formulas — Mifflin-St Jeor, Harris-Benedict, WHO BMI standards. Not approximations.
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100% Private
No data is stored or transmitted. Your health metrics stay on your device — we never see your inputs or results.
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Mobile-First Design
Built for phones first — 44px+ tap targets, fast load times, zero lag. Works perfectly on any device without an app download.
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Instant, No Signup
No registration, no email, no waiting. Open any tool and get results in under 30 seconds. All 20+ tools are permanently free.
FAQ
Frequently Asked Questions
The BMR Calculator uses the Mifflin-St Jeor equation as its primary formula — the most accurate method validated for modern populations. Harris-Benedict is also available for comparison. The result shows how many calories your body burns at complete rest.
The BMI Calculator uses the official WHO formula (weight in kg ÷ height in metres squared) and is accurate for adults aged 18–65. BMI has limitations — it doesn’t distinguish muscle from fat — so pair it with the Body Fat Percentage Calculator for a fuller picture.
Use the Calorie Calculator — it calculates your Total Daily Energy Expenditure (TDEE) based on your BMR and activity level. For weight loss, combine it with the Calorie Deficit Calculator to find your target intake safely.
Healthy ranges vary by sex and age. Generally: men 10–20% (athletic 6–13%), women 20–30% (athletic 14–20%). Use the Body Fat Percentage Calculator to estimate yours using the Navy method or BMI formula.
Adults typically need 7–9 hours. The Sleep Calculator goes further — it calculates exact bedtimes based on 90-minute sleep cycles so you wake up between cycles, feeling rested rather than groggy.
The Pregnancy Calculator and Pregnancy Weight Gain Calculator are built specifically for pregnancy tracking using WHO guidelines. General tools like BMI are not calibrated for pregnancy — always consult your doctor for clinical decisions.
Start with the Calorie Calculator to find your TDEE, then use the Macronutrient Calculator to split those calories into the right protein, carb and fat ratios for your goal. A common weight-loss split is 40% protein, 30% carbs, 30% fat.
Yes — all Sitnit health calculators are fully mobile-optimised with large tap targets and instant results. They work on any iPhone, Android or tablet without needing to download an app.
Not sure where to start?
Begin with the BMI Calculator — it takes 30 seconds and sets the baseline for everything else.
Start Free → BMI Calculator