TDEE Calculator

TDEE stands for total daily energy expenditure: the total energy a person uses in a day. It is difficult to measure accurately and it varies from one day to the next, so it is usually estimated from basal metabolic rate, activity level and the thermic effect of food.

The three parts of a day's burn

Basal metabolic rate

BMR is the rate at which you use energy at rest, in a temperate environment, with the digestive system inactive. It is the minimum needed to keep your vital organs running. For most people who are not athletes it accounts for 60% to 70% of the daily total, and the brain alone takes around a fifth of it.

Activity level

This covers deliberate exercise plus everything else you do at work and around the house. Formally it splits into the thermic effect of activity, meaning training, and non-exercise activity thermogenesis, meaning all the energy spent not sleeping, not eating and not doing anything sport-like. NEAT is the wildly variable one: walking, standing, fidgeting and carrying things can differ by as much as 2,000 calories a day between a desk worker who drives everywhere and someone on their feet all day.

Thermic effect of food

Also called specific dynamic action, this is the energy the body spends processing and using what you eat. It is often estimated at 10% of intake, and it varies a lot by food. Protein has a far larger thermic effect than dietary fat because it is harder to process: 20% to 30% of protein calories go on digesting it, against 5% to 10% for carbohydrate and almost nothing for fat.

How TDEE is calculated

The calculation starts with an estimate of BMR from physical characteristics, then multiplies by an activity factor.

TDEE = BMR x activity factor

where:

• BMR is basal metabolic rate in calories a day
• activity factor runs from 1.2 for sedentary to 1.9 for very intense daily training or a physical job

The commonly used BMR equations are Mifflin-St Jeor, Harris-Benedict and Katch-McArdle. They are broadly similar. Katch-McArdle, which works from lean body mass rather than total weight, can be more accurate for lean people who know their body fat percentage, since it accounts for the metabolic difference between muscle and fat.

The thermic effect of food is sometimes folded in as well, though it is not always included and it matters less than BMR and activity.

The activity factors

Exercise here means 15 to 30 minutes with your heart rate raised. Intense exercise means 45 to 120 minutes, and very intense means two hours or more.

Most people pick a level too high. Three gym sessions a week alongside a desk job and a car commute is light or moderate, not active. The gap matters: on the same body, moving from sedentary to extra active adds around 70% to the figure, which is the single largest source of error in any TDEE estimate.

A worked example

Take a 25-year-old man, 5 feet 10 inches, 165 pounds, exercising four or five times a week. Mifflin-St Jeor gives a BMR of 1,740 calories. Multiply by the moderate factor of 1.465 and TDEE comes to 2,549 calories a day, which is what he needs to hold his weight. His BMI is 23.7, inside the healthy 18.5 to 25 range.

A 25-year-old man of 180 cm and 65 kg at the same activity level has a BMR of 1,655 and a TDEE of 2,425. Same age, same sex, same training, 124 calories apart because of size alone.

Turning TDEE into a target

A pound of body fat holds roughly 3,500 calories, so a 500-calorie daily gap comes to a pound a week. Half a pound needs 250, and two pounds needs 1,000.

The calculator hides any loss target that falls under 1,500 calories for men or 1,200 for women, which is the floor Harvard Health puts on eating without medical supervision. If a 2 lb a week target would take you below it, that row disappears and a note appears instead. Someone with a lower TDEE simply cannot lose two pounds a week safely through diet alone.

The 3,500-calorie rule is a decent approximation for the first few months and it drifts after that. As you get lighter you burn less, so the intake that started as a deficit slowly becomes maintenance. Recalculate every 10 to 15 pounds rather than trusting one number for a year.

Why the estimate will not match you exactly

Every equation here was fitted to a population. Predicted BMR typically lands within about 10% of a measured value, which on a 2,500-calorie day is a 250-calorie band either way. Several things widen it.

Body composition. Mifflin-St Jeor uses total weight, so a muscular person and a heavier-set person of the same weight get the same answer. Katch-McArdle fixes this if you know your body fat percentage from a real measurement rather than a guess.

Adaptation. Sustained dieting lowers TDEE by more than the weight loss alone accounts for, partly through reduced NEAT. People in a deficit move less without noticing.

Health and medication. Thyroid conditions, several medications, pregnancy and breastfeeding all shift the figure, sometimes substantially.

Age. Resting expenditure declines with age, largely because lean mass declines. A large 2021 analysis published in Science found that expenditure adjusted for body composition is actually stable from about 20 to 60, and the fall people notice is mostly changing body composition and activity rather than metabolism itself slowing.

Environment. Cold increases expenditure through thermogenesis. Illness and fever raise it too.

Using the number properly

Treat the output as a starting point rather than a measurement. Eat at it for two or three weeks, weigh yourself under the same conditions each morning, and compare the seven-day average against the previous one. If your weight is holding steady, that is your real TDEE, and it is a better figure than any equation will give you.

Track trends rather than individual days. Glycogen binds about three grams of water per gram stored, so a carbohydrate-heavy weekend can add two or three pounds overnight and lose them again by midweek. Sodium, sleep and the menstrual cycle all move the scale for reasons unrelated to fat.

Be sceptical of fitness trackers here too. Wrist devices estimate energy expenditure from heart rate and motion, and validation studies routinely find errors of 20% to 90% on calorie burn even when heart rate itself is accurate. An equation and a tracker disagreeing tells you nothing about which is right.

If you are pregnant or breastfeeding, under 18, managing an eating disorder or working around a chronic condition, get a target from a clinician instead. These equations were never fitted to those situations.