Calorie Deficit & Weight Loss Calculator

A MET (Metabolic Equivalent of Task) expresses an activity’s energy cost relative to a standard resting reference. Higher-MET activities generally require more energy. The conventional reference is 3.5 ml of oxygen per kilogram per minute.

Standard METs do not precisely measure your own expenditure. Resting metabolism varies with factors including age, body size, sex and lean mass. Some Compendium values are estimates, while others are based on published measurements; neither is an individual measurement.

We add only energy above the standard resting component: (MET − 1) × 3.5 × weight in kg ÷ 200 × minutes. Subtracting 1 MET reduces double-counting of rest, but this standard reference is not identical to your predicted REE. The combination remains a simplified model.

Mifflin–St Jeor predicts resting energy expenditure: 10 × kg + 6.25 × cm − 5 × age + 5 for males, or −161 instead of +5 for females. It is a prediction, not a laboratory measurement. BMR, RMR and REE are sometimes used loosely in calculators but are not technically identical measurements.

Detailed mode adds net everyday movement and the daily average of weekly net exercise to REE. Missing movement can underestimate expenditure. Activity entries must not overlap. Do not enter a full working shift at a high MET if it includes substantial breaks or lighter work.

For maintenance, we divide this base expenditure by 1 − 0.10. TEF is modelled as 10% of intake. Evidence describes approximately 10% of daily expenditure on average; using a constant share of intake is our explicit educational simplification, not a fixed biological law.

When a percentage deficit is selected, desired deficit = maintenance × percentage. Alternatively, enter a desired daily deficit directly in kcal, such as 250 or 500; these examples are not personal recommendations. The same intake and TEF equations apply, and the result shows the equivalent percentage of maintenance with caution above 20%. Target intake = (base − desired deficit) ÷ (1 − 0.10). TEF at the target = target intake × 0.10. Actual estimated deficit = base + target TEF − intake. All calculations use unrounded values internally.

Quick mode replaces all detailed entries with separate, illustrative additions to REE. Everyday movement adds 8%, 20%, 35%, 55% or 75% for very low through very high activity. Planned exercise adds 0%, 10%, 20% or 30% for none through high. These are transparent broad assumptions, not Compendium METs, validated personal activity factors or measurements. The exact factors appear in your calculation.

A low-intake caution appears below 80% of predicted REE. This is an interface flag to prompt care, not a minimum intake or a validated safety threshold. An unflagged result is not a statement that an intake is suitable.

Weekly energy deficit is divided by 7,700 for a kilogram equivalent and by 3,500 for a pound equivalent. These conventional approximate constants are retained separately and do not convert perfectly between units. The result is not predicted fat loss. Static rules do not capture adaptation, body-composition changes or individual water changes.

• Mifflin MD et al. (1990), A new predictive equation for resting energy expenditure in healthy individuals, American Journal of Clinical Nutrition.
• 2024 Adult Compendium of Physical Activities. The local list contains 75 curated entries. Each selected activity shows its code; values were checked on 15 September 2026.
• Dietary Reference Intakes for Energy: factors affecting expenditure and requirements — including TEF and its variability.
• Hall KD, Why is the 3,500 kcal per pound weight loss rule wrong? — limitations of static calorie rules.
• NIDDK: research behind the Body Weight Planner — dynamic body-weight modelling.