What TDEE is made of
Total daily energy expenditure has three parts. Basal metabolic rate (BMR) — the energy your body uses at complete rest — is 60–75% of the total for most people. The thermic effect of food, the cost of digesting what you eat, is about 10%. Everything else is activity: deliberate exercise and the far larger sum of walking, standing, fidgeting and working. The calculator estimates BMR from the Mifflin-St Jeor equation (or Katch-McArdle if you enter body fat), then multiplies by an activity factor that stands in for the other two parts.
The table shows the six activity levels applied to a 30-year-old man, 5′10″ and 170 lb (BMR 1,737 kcal).
| Level | Factor | TDEE | Cut (−500) | Bulk (+500) |
|---|---|---|---|---|
| Sedentary | 1.2 | 2,085 | 1,585 | 2,585 |
| Light | 1.375 | 2,389 | 1,889 | 2,889 |
| Moderate | 1.465 | 2,545 | 2,045 | 3,045 |
| Active | 1.55 | 2,693 | 2,193 | 3,193 |
| Very active | 1.725 | 2,997 | 2,497 | 3,497 |
| Extra active | 1.9 | 3,301 | 2,801 | 3,801 |
Choosing an activity level honestly
Most people overestimate. 'Sedentary' is a desk job and no planned exercise. 'Light' is one to three sessions a week. 'Moderate' — the level between light and active that the classic five-step scale lacks — is four or five sessions a week, and is where most gym-goers actually fall. 'Active' means daily training or intense sessions three or four times a week; 'very active' is hard training six or seven days; 'extra active' is a physical job plus training. If in doubt, choose the lower level and let the scale correct you.
How age, sex and weight change the number
BMR falls with age — about 5 kcal a day per year in the Mifflin-St Jeor equation, so a 60-year-old burns roughly 150 kcal a day less than a 30-year-old of the same size. Women's BMR is about 166 kcal lower than men's at the same height, weight and age, reflecting a smaller average lean mass. Weight has the largest effect: every extra 10 lb adds about 45 kcal to BMR and 60–70 to TDEE at light activity.
| Age | Male | Female |
|---|---|---|
| 20 | 2,458 | 2,229 |
| 30 | 2,389 | 2,161 |
| 40 | 2,320 | 2,092 |
| 50 | 2,251 | 2,023 |
| 60 | 2,183 | 1,954 |
| 70 | 2,114 | 1,886 |
Weight and TDEE
Because heavier bodies cost more to run and move, TDEE falls as you lose weight. A 500 kcal deficit that works at 210 lb is a smaller deficit at 180 lb. Recalculate every 10 lb or so, or whenever weight change stalls for three weeks.
| Weight | BMR | TDEE (light) | TDEE (active) |
|---|---|---|---|
| 130 lb | 1,556 | 2,139 | 2,412 |
| 150 lb | 1,647 | 2,264 | 2,552 |
| 170 lb | 1,737 | 2,389 | 2,693 |
| 190 lb | 1,828 | 2,514 | 2,834 |
| 210 lb | 1,919 | 2,638 | 2,974 |
| 250 lb | 2,100 | 2,888 | 3,255 |
Turning a deficit into weight change
A pound of body fat holds roughly 3,500 kcal (7,700 per kg), so a daily deficit of 500 kcal is about a pound a week. That rule of thumb is a decent guide for the first months; over longer periods the body adapts, appetite and activity shift, and actual loss is usually somewhat slower than the arithmetic. A deficit of 500–750 kcal, or 15–25% of TDEE, is the range most guidelines recommend; larger deficits cost muscle and are hard to sustain. Do not eat below your BMR for long without medical supervision, and rarely below 1,200 kcal (women) or 1,500 (men).
| Daily deficit | Weekly deficit | Weekly loss | Time to lose 10 lb |
|---|---|---|---|
| 250 kcal/day | 1,750 | 0.5 lb / 0.23 kg | 20 weeks |
| 500 kcal/day | 3,500 | 1.0 lb / 0.45 kg | 10 weeks |
| 750 kcal/day | 5,250 | 1.5 lb / 0.68 kg | 7 weeks |
| 1000 kcal/day | 7,000 | 2.0 lb / 0.91 kg | 5 weeks |
Accuracy and adjusting
Mifflin-St Jeor predicts measured BMR within 10% for most people but can be off by 20% for some; the activity factor adds more uncertainty. Treat the TDEE as a starting estimate. Eat at it for two to three weeks, weigh yourself daily and average by week: if the average is stable, the estimate is right; if you are losing 1 lb a week, your true TDEE is about 500 kcal higher than what you are eating. The Katch-McArdle option, which uses lean mass, is more accurate for very lean or very muscular people whose weight-based BMR would be misjudged.
- BMR (Mifflin-St Jeor) = 10 × kg + 6.25 × cm − 5 × age + 5 (men) or − 161 (women).
- BMR (Katch-McArdle) = 370 + 21.6 × lean mass in kg.
- TDEE = BMR × activity factor (1.2 to 1.9).
- Check against real weight change and adjust by 100–200 kcal at a time.