Your Body, By the Numbers

Why Use LogiCalc? Your Complete Guide to Health & Nutrition Calculators

Understanding your body's numbers is the first step toward making real, lasting changes to your health. LogiCalc brings together the most-used health and nutrition calculators in one place — each built on the same evidence-based formulas used by registered dietitians, sports scientists, and clinical nutritionists worldwide.

What Is BMR and Why Does It Matter?

Your Basal Metabolic Rate (BMR)is the number of calories your body needs to sustain basic functions — breathing, circulation, cell repair — while completely at rest. It's the foundation of every other metabolic calculation. Without knowing your BMR, any calorie target you set is essentially a guess. LogiCalc's BMR Calculator uses the Mifflin-St Jeor equation, which research published in the American Journal of Clinical Nutrition and validated in a study in the Journal of the American Dietetic Association (2005) found to be the most accurate predictive equation for the majority of adults — more accurate than the older Harris-Benedict formula that many sites still use.

TDEE: From BMR to Real-World Calorie Needs

Total Daily Energy Expenditure (TDEE) takes your BMR and multiplies it by an activity factor that accounts for how much you actually move. A sedentary office worker and a construction worker who weigh exactly the same will have very different calorie needs — sometimes by 800–1,200 calories per day. Our TDEE Calculator applies the five standard activity multipliers (Sedentary, Lightly Active, Moderately Active, Very Active, Extra Active) so your result reflects your real lifestyle, not a generic average.

Understanding BMI — and Its Limitations

Body Mass Index (BMI) is the most widely used screening tool for weight classification, as detailed in the World Health Organisation obesity fact sheet, and used by healthcare providers globally. Our BMI Calculator gives you your score instantly alongside the standard WHO classification ranges (Underweight, Normal, Overweight, Obese I/II/III). It's worth noting what BMI does not measure: muscle mass, bone density, fat distribution, or cardiovascular fitness. A highly muscular athlete may show an "overweight" BMI while being in excellent health. Always use BMI as one data point alongside other metrics, not as a standalone verdict.

Protein, Carbohydrates, and Fat: The Macro Calculators

Once you know your TDEE, the next question is how to split those calories across the three macronutrients. The Institute of Medicine's Acceptable Macronutrient Distribution Ranges (AMDRs) and the Dietary Guidelines for Americans 2020–2025 set evidence-based targets: 45–65% of calories from carbohydrates, 10–35% from protein, and 20–35% from fats. These ranges are intentionally wide because the right split depends on your goal.

Someone focused on building muscle may push protein toward 30–35% of calories (roughly 1.6–2.2 g per kg of body weight, per a 2017 meta-analysis in the British Journal of Sports Medicine). Someone managing blood sugar may benefit from keeping carbohydrates toward the lower end of the AMDR. Our Protein Calculator, Carbohydrate Calculator, and Fat Intake Calculator all chain from your TDEE result so the outputs are consistent and personalised to your actual energy needs, in line with the WHO Protein and Amino Acid Requirements guidelines.

How LogiCalc Formulas Are Chosen

Every formula on this site is chosen based on validation against indirect calorimetry — the gold standard for measuring actual metabolic rate. We default to the Mifflin-St Jeor equation because a systematic review of 37 studies found it produced results within 10% of measured BMR for 82% of participants, outperforming both the Harris-Benedict (1919) and Cunningham equations for the general population. For BMI, we use the original Quetelet formula (weight in kg ÷ height in m²) as defined by the WHO. For protein ranges, we reference the most recent position statement from the International Society of Sports Nutrition (ISSN).

Frequently Asked Questions About Our Calculators

Are these calculators accurate? Yes — within the limits of predictive equations. No formula can replace a metabolic test in a clinical setting, but the equations we use are the same ones used in research and clinical practice. For most people, results are within 5–10% of actual measured values.

Do I need to create an account? No. Every calculator on LogiCalc is completely free and requires no registration. Your inputs are processed in your browser and are never stored on our servers.

How often should I recalculate? Recalculate your BMR and TDEE any time your weight changes by more than 5 kg, your activity level changes significantly, or you reach a new age bracket (every decade matters for metabolic rate).

Which calculator should I start with? Start with the BMR Calculator, then use that result in the TDEE Calculator. Once you have your TDEE, the macro calculators (protein, carbs, fat) all build on that number automatically.