Methodology

Calorie Calculator is designed as a fast planning tool, not a metabolic lab test. The estimate is generated from standard predictive equations, an activity multiplier, and a small set of goal presets that make the result easier to use in practice.

What the calculator estimates

The calculator estimates basal metabolic rate (BMR), then scales that number into total daily energy expenditure (TDEE). It also generates calorie targets for maintenance, weight loss, and muscle gain so the result is actionable instead of just descriptive.

Calculation flow used by this app

The app follows a simple sequence:

1. normalize height and weight into centimeters and kilograms
2. estimate BMR from the selected formula path
3. multiply BMR by the selected activity factor to estimate TDEE
4. build maintenance, deficit, and surplus planning targets from that TDEE

Default BMR formula: Mifflin-St Jeor

The default formula path uses Mifflin-St Jeor. In the app code, the equation is:

BMR = 10 × weightKg + 6.25 × heightCm - 5 × ageYears + sexOffset

sexOffset = +5 for male
sexOffset = -161 for female

This is the default because it works from common inputs most visitors can provide: weight, height, age, and sex.

Optional body-fat formula: Katch-McArdle

When body fat percentage is supplied and falls within the app's supported range, the calculator switches to a lean-mass-aware estimate based on Katch-McArdle:

leanBodyMassKg = weightKg × (1 - bodyFatPercent / 100)
BMR = 370 + 21.6 × leanBodyMassKg

In this implementation, body fat is only used when the value is between 3% and 60%. Outside that range, the app falls back to Mifflin-St Jeor.

TDEE formula used by the app

TDEE is not measured directly on this site. After BMR is estimated, the app multiplies it by an activity factor:

TDEE = BMR × activityMultiplier

The current multipliers in the app are:

• sedentary: 1.2
• light: 1.375
• moderate: 1.55
• very: 1.725
• athlete: 1.9

That means the final maintenance estimate is highly sensitive to honest activity selection. For practical help, read how to choose the right activity level.

How to read the result page

The BMR number is your estimated resting baseline. The TDEE number is the more useful maintenance starting point because it adds activity on top of that baseline.

The goal targets for cutting, maintenance, and bulking are planning presets built on top of TDEE. They are there to make the estimate easier to use, not to imply that the app measured your exact metabolism.

Why estimates can miss real maintenance

Predictive equations cannot fully capture individual differences in body composition, occupation, non-exercise movement, recovery, and adherence. Real maintenance calories can drift away from an estimate even when the formula logic is sound.

The intended workflow is to use the calculator as a starting point, then compare the result against 2 to 4 weeks of body-weight, performance, and recovery trends before making large changes.

Goal and macro outputs

The goal targets and macro splits are planning presets. They are meant to reduce friction after the estimate is calculated, not to replace individualized nutrition care. If you have a medical, clinical, or sport-specific nutrition requirement, the numbers here should be reviewed with a qualified professional.

The current goal presets are:

• maintenance: TDEE
• mild cut: TDEE - 500 kcal/day
• aggressive cut: TDEE - 750 kcal/day
• lean bulk: TDEE + 250 kcal/day
• aggressive bulk: TDEE + 500 kcal/day

Weekly change estimates use a simple energy-to-mass assumption, not a promise of actual scale movement:

estimatedWeeklyChangeKg = (deltaFromMaintenance × 7) / 7700

The current macro options are fixed percentage splits for the selected calorie target:

• moderate carb: 30% protein / 35% fat / 35% carbs
• lower carb: 40% protein / 40% fat / 20% carbs
• higher carb: 30% protein / 20% fat / 50% carbs

Protein and carbs are converted with 4 kcal per gram. Fat is converted with 9 kcal per gram. Calories are rounded for display.

Secondary stats

The result page also shows BMI and ideal-weight estimates as informational context. BMI is calculated from normalized metric inputs:

BMI = weightKg / (heightCm / 100)²

The BMI ranges used by the app are:

• underweight: less than 18.5
• normal: 18.5 to 24.99
• overweight: 25 to 29.99
• obese: 30 or higher

Ideal-weight estimates are shown with Devine, Hamwi, and Robinson formulas. They are secondary reference points, not calorie targets and not individualized health advice.

References and further reading

These links explain the formulas and energy-expenditure concepts this calculator is built around:

• Mifflin et al. (1990), original Mifflin-St Jeor paper
• Wikipedia: BMR equations based on total body weight
• Wikipedia: BMR equations based on lean body mass
• National Academies: Dietary Reference Intakes for Energy
• Wikipedia: Physical activity level
• Frankenfield et al. (2005), review of predictive resting metabolic rate equations

Update cadence

The methodology, copy, and related guides are reviewed whenever formulas, activity labels, or interpretation guidance change. The calculator remains intentionally simple, so changes are published directly in the app rather than hidden behind an account or proprietary scoring model.

For a broader explanation of how to use the estimate, see the calorie calculator guides or return to the calculator.