Where to start
If you're trying to change your weight, start with TDEE — it tells you roughly how many calories you burn in a day, and every other nutrition decision follows from it. From there the Calorie Deficit Planner turns a goal weight and a target date into a daily calorie number, and the Macro Calculator splits that number into protein, carbs and fat.
Body composition vs body weight
Scale weight alone is a poor progress signal — it swings with water, food and glycogen. BMI is a crude screening number that doesn't distinguish muscle from fat, which is why a lean athlete can read as "overweight". Body Fat % (US Navy method), Lean Body Mass and Waist-to-Hip Ratio describe your actual composition far better, and waist-to-height in particular tracks health risk more closely than BMI does.
Training numbers
For strength work, One-Rep Max estimates your true max from a set you've actually done, and gives the percentage table most programmes are written around. For conditioning, Heart Rate Zones converts your age into the five training zones, and Running Pace turns a pace into finish times for common race distances.
A note on accuracy
These are formula-based estimates, not clinical measurements. Equations like Mifflin-St Jeor (used for BMR and TDEE) are fitted to population averages, so an individual can sit several hundred calories either side of the prediction. Use the number as a starting point, track real results for two or three weeks, then adjust. None of this is medical advice.
Which calculator should I use to lose weight?
Start with TDEE to find your maintenance calories, then use the Calorie Deficit Planner to set a daily target for your goal weight and date. The Macro Calculator then splits those calories into protein, carbs and fat.
Is BMI a good measure of health?
It's a rough screening tool, not a diagnosis. BMI can't tell muscle from fat, so it misclassifies muscular people as overweight and can miss excess fat in people with low muscle mass. Waist-to-height ratio and body fat percentage are better individual indicators.
How accurate are these fitness calculators?
They use published, peer-reviewed formulas (Mifflin-St Jeor, Katch-McArdle, US Navy, Epley) and are accurate to within roughly 5–10% for most people. Individual metabolism varies, so treat the result as a starting estimate and adjust based on real-world results.
Do I need to create an account?
No. Every calculator runs entirely in your browser, nothing is sent to a server, and there is no sign-up. Your inputs stay on your device.