TDEE and Activity Factor

Foundation · 11 min

From BMR to TDEE

BMR describes only the cost of rest; yet during the day you walk, work, climb stairs, perhaps exercise. The estimate of total daily energy expenditure is called TDEE, and the most common method is a single multiplication: TDEE = BMR × activity factor. The factor is a number between 1.2 and 1.9 that roughly represents how active your lifestyle is. The multiplication adds the share of daily movement on top of the resting cost.

The factor approach is rough but useful: without keeping a step-by-step activity log, it lets a single question take the whole of daily life into account. That simplicity is also why the method has been in such widespread use for decades.

The factor table

The commonly used steps are these:

The steps are rough representations, not sharp boundaries; if you feel you sit between two steps, using a value in between is perfectly possible.

When reading the table, count non-exercise movement too: walking to work, working on your feet and housework all affect which step the factor lands on, even though they do not count as training.

The matter of honest selection

Choosing the factor is the biggest source of error in this calculation, and the error is almost always in the same direction: people tend to rate their activity higher than it is. For someone who goes to the gym twice a week but spends the rest of the day at a desk, 1.55 is usually too high; 1.375 may be more realistic. A practical rule: when in doubt, choose the lower step and adjust upward if a few weeks of observation call for it. The hours spent sitting through the rest of the day count just as much as the length of the workout.

A simple indicator like a step count can be used to test your choice: a life that stays under a few thousand steps a day sits closer to the lower steps, despite two hours of weekly training.

A worked example from start to finish

Let us continue the example from the previous lesson: the estimated BMR of a 30-year-old woman, 65 kg and 165 cm, came out at about 1370 kcal. If she walks two or three days a week and spends most of the rest of her time at a desk, 1.375 is a reasonable choice: 1370 × 1.375 = 1884. The estimated TDEE is about 1880-1890 kcal per day. Had she chosen 1.55, the result would have been about 2120 kcal; the gap between the two choices exceeds 230 kcal. A seemingly small difference in the factor makes a large difference in the result; and that opens the door to the next lesson's subject, uncertainty.

This gap also explains why calculators give different results: the formula is usually the same, and the difference lies in the activity level you ticked. The first place to look for anyone wanting to change the result is the factor choice.