Trust the assumptions you can inspect.

1. Resting energy expenditure

Mifflin-St Jeor

For men: BMR = 10W + 6.25H − 5A + 5. For women: BMR = 10W + 6.25H − 5A − 161. Weight (W) is kilograms, height (H) is centimeters, and age (A) is years.

The equation was derived from 498 healthy adults. A later validation found it predicted measured resting metabolism within 10% for 78% of nonhospitalized subjects, better than the compared Harris-Benedict and Owen equations but still imperfect.

Katch-McArdle when body fat is supplied

When body-fat percentage is provided, lean mass is estimated and BMR = 370 + 21.6 × lean mass in kg. Deficit Compass uses the activity-adjusted result as the primary estimate in that case. Body-fat measurement error can outweigh the formula's potential advantage, so the result remains a prediction rather than measured truth.

2. Total daily energy expenditure

BMR is multiplied by one of five conventional activity factors: sedentary 1.2, light 1.375, moderate 1.55, heavy 1.725, or athlete/very active 1.9.

Activity selection is the least precise input. Controlled-feeding research has found high activity factors can overestimate energy requirements. Compare adjacent levels in the TDEE calculator and use two-week calibration rather than assuming the label is exact.

3. Primary estimate and comparison models

The main Deficit Compass result uses activity-adjusted Mifflin-St Jeor when body fat is unavailable and activity-adjusted Katch-McArdle when body fat is supplied. The calculator also displays four values from the original Caloric Planning sheet:

• Body weight in pounds × 15
• Body weight in pounds × 10
• Mifflin BMR × selected activity factor
• Revised Harris-Benedict BMR × selected activity factor

The four-value average is a transparent comparison heuristic, not a peer-reviewed or clinically validated equation. A 12-profile benchmark found an average 989 kcal/day range across the four component methods, driven largely by weight-only shortcuts. The blend remains visible to preserve the planning sheet's context, but it does not determine the recommendation. Inspect the benchmark and download its data.

All equations are starting estimates. Real trend calibration should outrank every prediction after sufficient consistent data.

Optional deeper reading: Compare five books for Mifflin-St Jeor, Harris-Benedict, Katch-McArdle, and modern energy-requirement methods. The guide retains the primary papers and clearly separates free sources from paid Amazon links.

4. Deficit and goal timeline

The selected pace is a percentage of current body weight per week. That target is converted with the short-term approximation of 3,500 calories per pound, divided across seven days. The requested deficit is capped at the lower of 30% of maintenance or 1,000 calories per day.

General intake floors are 1,500 calories for men and 1,200 for women. These are guardrails, not individualized prescriptions. If estimated maintenance is within 150 calories of the relevant floor, Deficit Compass applies no automated deficit and directs the user to qualified guidance.

Goal dates use a linear projection. Long-term weight loss is not linear, so dates should be treated as planning signals and recalculated as body weight changes. NIDDK's dynamic Body Weight Planner is a stronger model for long forecasts.

5. Macro allocation

The main deficit calculator starts protein near 0.9 grams per pound of body weight, or approximately one gram per pound of estimated lean mass when body fat is supplied, constrained to 110-240 grams. Fat starts near 0.7 grams per kilogram, constrained to 40-95 grams. Carbohydrate receives remaining calories.

The standalone macro calculator uses a separate goal-specific rule set: protein starts at 0.9 grams per pound for a cut and 0.8 for maintenance or gain, constrained to 90-260 grams; fat starts at 0.32 grams per pound for a cut or maintenance and 0.35 for gain, constrained to 40-110 grams. If the protein and fat defaults exceed the entered calories, it reports no viable split instead of presenting an internally inconsistent target.

Both sets are convenient product defaults awaiting qualified review, not diagnoses of nutrient needs. The review scope explicitly asks whether they should be harmonized, narrowed, or removed.

6. Two-week calibration

Observed maintenance is estimated as average daily intake + (weekly pounds lost × 3,500 ÷ 7). If body weight increased, weekly loss is entered as a negative number.

This calculation is highly sensitive to incomplete food logging and short-term water changes. Use at least 14 days, compare weekly averages, and repeat before making another adjustment.

Primary sources

Research and public guidance

• Mifflin et al. (1990), A new predictive equation for resting energy expenditure
• Roza and Shizgal (1984), revised Harris-Benedict equation
• Frankenfield et al. (2003), validation of established resting metabolic equations
• Lin et al. (2003), estimation of energy requirements in a controlled feeding trial
• CDC, gradual weight loss guidance
• NIDDK Body Weight Planner

Built and documented by Builderfox LLC. Not yet medically reviewed. Report errors through Contact and review material changes in the correction log.

Creation note: Formula implementation and benchmark arithmetic were checked with software. AI-assisted research organization and drafting were manually reviewed against the linked sources, published equations, and downloadable data. See the editorial policy.