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 comparison

When body-fat percentage is provided, lean mass is estimated and BMR = 370 + 21.6 × lean mass in kg. Body-fat measurement error can easily outweigh the benefit of the formula, so the result is shown as a comparison rather than treated as 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. The four-model maintenance blend

The main Deficit Compass result averages four values from Aaron Bergquist's planning sheet:

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

This blend is a transparent project heuristic, not a peer-reviewed or clinically validated equation. It is included to honor the original planning model and reduce dependence on one formula. The component values are always shown so the spread is visible. Real trend calibration should outrank the blend after sufficient consistent data.

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 a practical range. Fat starts near 0.7 grams per kilogram. Carbohydrate receives remaining calories.

These are convenient starting rules, not a diagnosis of nutrient needs. The macro calculator exposes the allocation separately so users can see the tradeoff.

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 Aaron Bergquist. Not yet medically reviewed. Report errors or propose corrections at hello@deficitcompass.com.