What is TDEE, and how is it calculated?

What makes up your TDEE?

Your daily energy use has three parts: resting energy, digestion and physical activity. That is how a 2004 review of diet-induced thermogenesis describes daily energy expenditure, and each part behaves differently.

Digestion is the smallest of the three. The same review puts it at about 10 percent of the energy eaten on a mixed diet, higher when meals are rich in protein or alcohol and lower when they are rich in fat. Of the three macronutrients, protein takes the most energy to process: 20 to 30 percent of its calories, compared with 5 to 10 percent for carbohydrate and 0 to 3 percent for fat.

Everyday movement is the wild card. A 2002 review of non-exercise activity thermogenesis, or NEAT, defines it as the energy spent on everything that isn't sleeping, eating or sports-like exercise: walking to work, typing, yard work, fidgeting. It explains most of the energy people use beyond resting, and it is high in manual and farm workers.

How is TDEE calculated?

Most calculators work in two steps: estimate resting energy, then scale it up for how active you are. The usual resting-energy formula is the Mifflin–St Jeor equation, published in 1990 from measurements of 498 healthy adults aged 19 to 78.

• Men: 10 × weight in kg + 6.25 × height in cm − 5 × age in years + 5
• Women: 10 × weight in kg + 6.25 × height in cm − 5 × age in years − 161

For a 40-year-old woman who is 163 cm (5 ft 4 in) tall and weighs 68 kg (150 lb), that works out to about 1,340 calories at rest. The activity step then multiplies resting energy by a factor for your usual week. The more you move, the bigger the factor and the larger your total.

The 2020–2025 Dietary Guidelines show how much activity changes the total. For women aged 36 to 40, they estimated about 1,800 calories a day for a sedentary lifestyle, 2,000 for a moderately active one and 2,200 for an active one. For men of the same age, the estimates were 2,400, 2,600 and 2,800.

In those tables, sedentary means only the activity of everyday independent living. Moderately active means the equivalent of walking about 1.5 to 3 miles a day at 3 to 4 miles per hour, and active means walking more than 3 miles a day at that pace.

How accurate is a TDEE estimate?

It's a starting point, and it can be off by a meaningful amount for any one person. A 2005 systematic review found Mifflin–St Jeor the most reliable of the four resting-energy equations most used in practice: it came within 10 percent of measured values for more people than any other. The same review warned of noteworthy errors for individuals, and noted that older adults and U.S. ethnic minorities were underrepresented in the research.

The activity part adds more uncertainty, because people tend to overestimate how much they move. In a 1992 study of people who said they couldn't lose weight on a low-calorie diet, participants overreported their physical activity by 51 percent on average.

TDEE also moves over time. Weight is part of the formula, so your estimate falls as you lose weight. The 2002 NEAT review found that everyday movement rises with overfeeding and falls with underfeeding, so your body may spend less when you eat less.

How can you find your real TDEE?

Compare what you eat with what the scale does over a few weeks. If your weight holds steady while you log consistently, your average intake is close to your real TDEE. If your weight falls, your TDEE is higher than your intake, and if it rises, it's lower.

The 2020–2025 Dietary Guidelines make the same point: their calorie figures are estimates, and the best way to judge intake against needs is to watch body weight. Use weekly averages rather than single weigh-ins. In a 2020 study of 1,421 people's weigh-ins, weight rose on weekends and fell on weekdays, on top of any longer-term trend.