Calorie Calculator

Calorie calculators produce a pair of figures, and confusing them is the most common reason a plan fails.

• BMR - basal metabolic rate. What your body burns at complete rest to keep you alive: breathing, circulation, temperature, cell repair. Typically 60-75% of everything you burn.
• TDEE - total daily energy expenditure. BMR plus the energy of living: walking, digesting, working, exercising. This is the number to compare against food intake.
• Eating at TDEE maintains weight. Below it loses, above it gains - but only as an average over days, never precisely on any single day.

Note. Because BMR dominates the total, non-exercise movement often matters more than structured workouts. Someone who walks all day can burn several hundred calories more than a sedentary person who trains for 45 minutes.

The Mifflin-St Jeor equation is generally regarded as the most reliable of the simple estimates for adults.

Older equations - Harris-Benedict and Katch-McArdle - are still used. Katch-McArdle requires body-fat percentage and is preferable for muscular individuals, because it is the only common formula that estimates lean mass directly rather than ignoring it.

A 30-year-old man, 80 kg, 178 cm, moderately active.

A deficit of 500 calories a day is the conventional target for losing roughly half a kilogram a week, on the basis that a kilogram of body fat carries about 7,700 calories. In practice the relationship is not perfectly linear - metabolism adapts, water weight shifts, and the estimate is a guide rather than a guarantee.

Note. Roughly 3,500 calories used to be cited as the equivalent of a pound of fat. That figure is an oversimplification: fat tissue is not pure lipid, and energy expenditure falls as weight falls. Treat calorie targets as starting points to be adjusted from observed results.

• The equations are population averages. Individual variation of +/- 10% or more around the predicted BMR is entirely normal - meaning two identical people can differ by 200-300 calories a day.
• Activity multipliers are subjective. "Moderately active" means different things to different people, and most people overestimate. If the number does not match what happens on the scale over three weeks, the multiplier is wrong, not the formula.
• Thermic effect of food varies by macro-nutrient: protein costs roughly 20-30% of its own calories to process, carbohydrate 5-10%, fat 0-3%. Diets high in protein therefore produce a slightly higher real expenditure than the same calories from fat.
• Adaptive thermogenesis - prolonged restriction reduces expenditure beyond what the formula predicts, so a target that worked at the start under-delivers later.
• It cannot count accurately. Food databases and portion estimates carry their own error, often 10-20% on home-prepared meals.

1. Track for two to three weeks before changing anything. Compare intake against weight trend rather than daily readings, which are mostly water.
2. Adjust in increments of roughly 100-200 calories rather than large cuts. Large deficits cost muscle and drive adaptation.
3. Weigh yourself consistently - same time, same conditions, and use the weekly average.
4. Recalculate as you lose - a lighter body burns less, so the original target becomes maintenance at the new weight.
5. Do not eat back exercise calories in full. Fitness trackers commonly overestimate expenditure by 20-40%.
6. Prioritise protein and fibre for satiety at the same calorie level.
7. Ignore the precision. A plan built on a number accurate to +/- 10% still works if it is followed and adjusted from results.