Methodology and Sources

Units

1 lb = 0.45359237 kg (exact). 1 in = 2.54 cm (exact). Source: NIST SP 811.
Inputs are converted to kg and cm at full precision before any formula runs; the equation shown on the page displays them to one decimal.

Resting equations

Mifflin-St Jeor (default). Men: 10 × kg + 6.25 × cm − 5 × age + 5. Women: 10 × kg + 6.25 × cm − 5 × age − 161. Mifflin et al., 1990.
Harris-Benedict, revised. Men: 88.362 + 13.397 × kg + 4.799 × cm − 5.677 × age. Women: 447.593 + 9.247 × kg + 3.098 × cm − 4.330 × age. Roza and Shizgal, 1984.
Katch-McArdle. 370 + 21.6 × lean mass (kg), lean mass = weight × (1 − body fat). McArdle, Katch and Katch, Exercise Physiology.
Cunningham. 500 + 22 × lean mass (kg). Cunningham, 1980.
The lean-mass equations are only computed when a body-fat percentage between 3 and 70 is entered. They are shown for comparison; the headline number always uses Mifflin-St Jeor.

Activity factors

Sedentary × 1.2 · Lightly active × 1.375 · Moderately active × 1.55 · Very active × 1.725 · Extra active × 1.9. These are the conventional multipliers used across the field; they are a convention descended from the Harris-Benedict tradition rather than the result of one study, and they include the thermic effect of food. The "TDEE at each level" table in the results multiplies the same BMR by each factor.

Activity helper

The optional three-question helper estimates a physical activity level (PAL) and snaps it to the nearest conventional factor. It is a rule of thumb, built as follows:

Job baseline and implied steps: mostly sitting 1.2 (about 3,000 steps); on my feet part of the day 1.3 (about 6,000 steps); on my feet most of the day 1.4 (about 9,000 steps); heavy physical work 1.55 (about 11,000 steps).
Training: sessions per week × net MET value × hours per session ÷ 168 hours. Net METs: light 2, moderate 4, vigorous 7, typical values above rest from the 2011 Compendium of Physical Activities for walking and yoga, resistance training and moderate cycling, and running, HIIT and team sports respectively.
Steps (optional): (entered steps − steps implied by the job) ÷ 1,000 × 0.0167, which treats 1,000 steps as about 10 minutes of walking at roughly 2.5 METs above rest.
Snapping: the estimate is clamped to 1.15 to 2.2 and mapped to the nearest factor using the midpoints 1.2875, 1.4625, 1.6375 and 1.8125. Anyone who trains at least once a week is placed no lower than Lightly active, because Sedentary is defined as little or no exercise. Estimates within 0.03 of a midpoint are flagged as borderline.

The helper is deliberately conservative. Validation against measured energy expenditure has not been done; the tracker on this site is the way to check it for yourself.

Range, goals and floors

Range: ±10% around the TDEE. In the systematic review by Frankenfield and colleagues (2005), Mifflin-St Jeor predicted measured resting metabolic rate within 10% in the largest share of nonobese and obese adults of the four equations compared; the activity factor adds error beyond that, so ±10% is a floor on the true uncertainty, not a ceiling.
Deficits and surpluses: −250, −500, −750 and −1,000 kcal/day for 0.5, 1, 1.5 and 2 lb a week; +250 and +500 for gaining. These use the 3,500 kcal per pound approximation. Hall and colleagues (2011) showed that the real response is slower and flattens over time, which is why the site asks for a recalculation every 10 lb and offers the tracker.
Floors: deficit targets are capped at 1,200 kcal for women and 1,500 kcal for men, a widely used practical threshold for unsupervised dieting rather than a finding from a specific study. When a cap applies, the page shows the slower loss it implies. No target is ever raised above TDEE for a "lose" goal.
Macros: protein 1.6 g per kg of body weight (the breakpoint beyond which additional protein did not add muscle in the meta-regression by Morton and colleagues, 2018); fat 25% of calories at 9 kcal/g; carbohydrate the remainder at 4 kcal/g. If protein alone would exceed the calories, carbohydrate is set to zero and fat fills what remains.
Pregnancy and breastfeeding: pregnant, 2nd trimester +340; pregnant, 3rd trimester +452; breastfeeding, baby under 6 months +330; breastfeeding, baby 7 to 12 months +400 kcal/day, the Dietary Reference Intake additions as reported in Kominiarek and Rajan (2016) and the Dietary Guidelines for Americans 2020–2025. Applied only when the user selects a stage and only for female.
BMI: kg ÷ m², categories per the CDC (under 18.5, 18.5 to 24.9, 25 to 29.9, 30 and above). Shown for context; not used in any calculation.

Adaptive tracker

Observed TDEE = mean logged intake − (daily weight trend in lb × 3,500). The trend is the slope of an ordinary least-squares line through every weigh-in, which damps day-to-day water changes. The page requires at least 4 weigh-ins spanning 14 or more days and at least 10 days of intake before showing a result. All data stays in the browser's local storage; export and import use a three-column CSV (date, weight_lb, calories) or JSON.

Rounding

All math runs at full precision; rounding happens only when a number is displayed.
Calories are shown as whole numbers with a thousands separator. Weight and height in the equation line are shown to one decimal.
The example results in the text, the chart and the live calculator are produced by the same code, so they always agree.

What the site does not do

No equation on this page measures anything about you. The site does not adjust for thyroid status, medications, menstrual cycle, menopause, PCOS or ethnicity, because no validated correction with a reliable number exists for a consumer calculator. Where other sites apply such adjustments without a source, this one does not.

Sources

Corrections

If you find an error, write to hello@tdeecalculator.fitness. Confirmed errors are fixed in the engine or the source list, which corrects every page that uses the value, and the change is noted here.