The formula
TDEE = BMR × activity factor (1.2 to 1.9)
Where it comes from
Total daily energy expenditure is your basal rate plus everything else: exercise, walking, fidgeting and even digestion. The activity multiplier is a blunt instrument, but it is the only practical way to turn a resting figure into a daily one without a laboratory.
How to work it out by hand
- Work out your basal metabolic rate first
- Pick the activity factor that matches your week honestly
- Multiply the two
- Subtract about 500 kcal a day to lose half a kilo a week
What is worth knowing
Almost everyone overestimates their activity level, which is the single biggest source of error here. A desk job with three gym sessions is 'light to moderate', not 'heavy' — heavy means manual labour or serious daily training. The correction is empirical: eat at the calculated figure for two or three weeks, weigh yourself at the same time each morning, and adjust from the trend rather than from any single day. A kilo of fat is about 7,700 kcal, so a 500 kcal daily deficit is roughly half a kilo a week.