How to Calculate Your TDEE Step by Step: A Complete Worked Example

Step 1: Estimate Your Basal Metabolic Rate

Basal metabolic rate (BMR) is the energy you would burn lying still for a day. The Mifflin-St Jeor equation estimates it as 10 × weight in kilograms + 6.25 × height in centimeters − 5 × age − 161 for women (+5 for men). For our example: 650 + 1,031.25 − 175 − 161 = 1,345 calories per day.

That number is the floor for basic life functions: breathing, circulation, temperature regulation, and cell repair. It does not include a single step of walking, which is why eating only your BMR is not a sensible target for most people.

Step 2: Choose an Honest Activity Factor

Multiply BMR by an activity factor: 1.2 for sedentary, 1.375 for lightly active, 1.55 for moderately active, 1.725 for very active, and 1.9 for extremely active. The most common error is choosing too high a category. A person who sits at a desk and trains three times a week typically belongs in lightly active (1.375), not moderately active, because the multiplier averages all seven days and all waking hours.

For the example, 1,345 × 1.375 = 1,850 calories. If she had picked 1.55 instead, the result would be 2,085, an overstatement of 235 calories that would erase a good portion of any planned deficit.

Step 3: Set a Goal Relative to TDEE

For fat loss, a deficit of 10% to 20% of TDEE is a sustainable range for most people. For this woman, 20% below 1,850 is about 1,480 calories, and 15% below is about 1,572. For maintenance, eat at TDEE. For muscle gain, aim for a surplus of 5% to 10%, around 1,940 to 2,035 calories.

Percentages scale better than fixed numbers like 500 calories. A fixed 500-calorie cut is 27% of this woman's TDEE, which is aggressive, but only 17% for someone with a 3,000-calorie TDEE.

Step 4: Verify With Real Data

Eat at your estimated target for two to three weeks while weighing yourself daily or most days, in the morning, under similar conditions. Average the weekly values. A weight change of 0.5 kg over two weeks equals roughly 3,850 calories (7,700 per kg), or about 275 calories per day. Compare that to what you expected.

If you aimed at a 370-calorie daily deficit but your weight did not move, your actual TDEE is about 370 calories lower than estimated, or you under-tracked your food. Adjust your target by that difference and test again. This feedback loop is far more reliable than any equation.

Things That Change Your TDEE Over Time

Your TDEE is not fixed. It falls as you lose weight, because a smaller body costs less to maintain and move. It rises with muscle gain, higher daily step counts, and more intense training. Age gradually reduces it, mainly through loss of lean mass. Large changes in non-exercise movement, such as fidgeting and walking, can swing daily expenditure by several hundred calories without any formal workout.

Recalculate after every 5 kg of weight change or whenever your routine changes substantially. Treat the estimate as a working hypothesis, not a fact.

Common Mistakes

Counting exercise twice by choosing a high activity factor and then eating back workout calories from a wearable; relying on a wearable's calorie number without cross-checking; comparing one-day weights instead of weekly averages; forgetting weekend eating, which can erase a weekday deficit; and following a deficit so aggressive it cannot be sustained.