Fitness calculators that show their working
Updated 10 September 2026
Use them right here — nothing is saved or sent anywhere. Below each one, the exact published formula it uses and, just as importantly, what the number cannot tell you.
Calorie and TDEE calculator
Your BMR, your TDEE and a daily calorie target for your goal — the same formulas the app starts from, before it shifts the target by training phase
Protein calculator
How many grams per day, from your weight and goal
BMI calculator
Weight-to-height ratio — a rough screening number, honestly labelled
One-rep max calculator
Estimate your 1RM from any hard set — no max attempt needed
Nothing you type here is stored or sent anywhere — the calculation happens in your browser and disappears when you leave. These are general estimates, not medical advice; see the notes under each formula below.
The formulas, explained
BMR calculator: Basal Metabolic Rate
Formula
Men: (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
Women: (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
What it is
The energy your body uses at complete rest, just to keep your organs running. It is the floor of your daily calorie needs, not a target to eat at.
How this app uses it
Top 1% Fit uses the Mifflin-St Jeor equation, one of the most widely used formulas for estimating resting energy expenditure.
What it cannot tell you
This is a population-based estimate. Individual metabolic rate varies with body composition, hormones and other factors it cannot see.
TDEE calculator: Total Daily Energy Expenditure
Formula
TDEE = BMR × activity factor (1.25 sedentary → 1.72 very active)
What it is
An estimate of everything you burn in a day, including walking, training and daily movement. It is the number your calorie target is built from.
How this app uses it
The activity multiplier is chosen from how you describe a typical week. Your calorie target is then adjusted from TDEE by your goal and current training phase.
What it cannot tell you
Activity multipliers are broad bands. If your weight is not moving as expected after two or three weeks, the multiplier is usually the thing to revisit.
BMI — Body Mass Index
Formula
BMI = weight kg ÷ (height m)²
What it is
A ratio of weight to height, used as a rough population-level screening figure. Under the WHO general bands, below 18.5 is classed as underweight, 18.5–24.9 healthy, 25–29.9 overweight and 30+ obese. For South Asian populations health risk rises at lower values, and many Indian guidelines treat 23 and above as overweight.
How this app uses it
Calculated directly from the height and weight in your profile.
What it cannot tell you
BMI cannot distinguish muscle from fat. A muscular person can read as "overweight" while carrying very little body fat. Treat waist measurement and progress photos as better signals.
Macros — protein, carbohydrate and fat
Formula
Protein: 1.9–2.2 g per kg of reference weight (varies by goal)
Fat: ~0.85 g per kg of reference weight, trimmed first if calories run short
Carbohydrate: whatever calories remain
Reference weight: your weight, capped at the weight that would put your height at a BMI of 27.5
What it is
How your daily calories are split across the three macronutrients. Protein is set first because it is the one that most affects whether you keep muscle.
How this app uses it
Protein and fat are set from body weight, then carbohydrate fills the remaining calories. Protein provides 4 kcal per gram, carbohydrate 4, fat 9.
What it cannot tell you
These are starting points, not precise requirements. Consistency across a week matters far more than hitting an exact number on any single day.
1RM — estimated one-rep max
Formula
Estimated 1RM = weight × (1 + reps ÷ 30)
What it is
An estimate of the heaviest single rep you could perform, worked out from a set you already completed — without having to attempt a true maximum.
How this app uses it
Top 1% Fit uses the Epley formula and records your best estimate per exercise automatically as you log sets.
What it cannot tell you
Accuracy drops as rep count rises; estimates from sets above roughly 10 reps become unreliable. It is a progress marker, not a number to train to.
Body fat estimate
Formula
Deurenberg: (1.20 × BMI) + (0.23 × age) − (10.8 × sex) − 5.4
What it is
A rough indication of body fat percentage derived from BMI, age and sex.
How this app uses it
Calculated from your profile using the Deurenberg equation, and labelled as an estimate everywhere it appears in the app.
What it cannot tell you
This is the least precise figure in the app. Because it is derived from BMI, it inherits the same blindness to muscle mass. Use the direction it moves over time, never the absolute number.
Common questions
What is BMR?
Basal Metabolic Rate is the energy your body uses at complete rest to keep basic functions running. Top 1% Fit calculates it with the Mifflin-St Jeor equation, which is one of the most widely used formulas for this estimate.
What is TDEE?
Total Daily Energy Expenditure is your BMR multiplied by an activity factor between 1.25 and 1.72, giving an estimate of the total calories you burn in a day including movement and training.
How much protein should I eat?
Research on resistance training generally supports roughly 1.6 to 2.2 grams of protein per kilogram of body weight per day for people trying to build or retain muscle.
How is a one-rep max estimated?
Top 1% Fit uses the Epley formula: estimated 1RM equals weight multiplied by (1 + reps / 30). It is an estimate from a submaximal set, not a tested maximum.
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