Health and Fitness Calculators
Calculate BMI, BMR, TDEE, macros, and daily water needs. Straightforward fitness math based on formulas used by nutritionists and trainers.
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Every category on ConvertNow, each one free and updated as new tools launch.
Understanding Health & Fitness
What these tools are for, and how to get the most reliable result from them.
Numbers that support your goals
Whether you are tracking weight, planning meals, or building a training program, these calculators turn your height, weight and activity level into numbers you can actually act on.
Built on established formulas
The BMR calculator uses the Mifflin St Jeor equation, widely considered more accurate for most adults than older methods. BMI and TDEE follow the same standard formulas used across fitness and nutrition guidance.
A starting point, not a diagnosis
These tools provide general estimates, not a medical assessment. They do not replace advice from a doctor, registered dietitian or other qualified health professional, particularly if you have a medical condition, are pregnant, or are starting a new diet or exercise program.
FAQ: Health and Fitness Calculators
Straight answers to what people ask most about these tools.
Are these calculators a substitute for medical advice?
No. These tools provide general estimates based on standard formulas. They are not a diagnosis and do not replace advice from a doctor, registered dietitian or other qualified health professional, especially if you have a medical condition or are pregnant.
How accurate is BMI as a health measure?
BMI is a quick screening estimate based on height and weight only. It does not account for muscle mass, bone density or body composition, so athletes and very muscular people often score higher than their actual body fat would suggest.
What is the difference between BMR and TDEE?
BMR is the energy your body needs at complete rest just to function. TDEE adds your daily activity on top of that, giving a more realistic total calorie estimate for weight goals.
Which formula does the BMR calculator use?
The Mifflin St Jeor equation, which is widely regarded as more accurate for most adults than older formulas like Harris Benedict.
How is my daily water intake target calculated?
It is estimated from your body weight and activity level. Individual needs vary with climate, health conditions and diet, so treat the result as a general guide rather than a strict target.
Can I use these calculators for a child or teenager?
These formulas are calibrated for adults. Growth charts and pediatric specific tools are more appropriate for children and teenagers, so check with a pediatrician for that age group.
How to use these tools
The same simple flow works across every tool on this page.
Pick a calculator
Choose the one that matches your goal, weight, energy needs, or hydration.
Enter your details
Height, weight, age and activity level, wherever the calculator asks for them.
Get an instant estimate
Based on standard, widely used fitness formulas.
Recalculate any time
Update the numbers whenever your weight or activity level changes.
Syntax and reference
Formulas, formats and quick references used across this category.
BMI formula
BMI = weight in kilograms / (height in metres)^2BMR formula, Mifflin St Jeor, for men
BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5TDEE activity multipliers
| Sedentary | BMR x 1.2 |
|---|---|
| Light activity | BMR x 1.375 |
| Moderate activity | BMR x 1.55 |
| Very active | BMR x 1.725 |
Built to be trusted, every time
No dark patterns, no forced accounts, and nothing you type is kept longer than it takes to give you an answer.
Nothing you enter is stored
Inputs are used only to generate your result, in that moment.
Free, with no catch
No sign up, no trial period, no hidden paywall on any tool.
Works on any device
Every tool is built to work on desktop, tablet and mobile.