TDEE Calculator

How is TDEE calculated?

TDEE is calculated in two steps: estimate BMR (basal metabolic rate), then multiply by an activity factor that accounts for everything you do on top of just existing.

1Estimating BMR

Your BMR is the calories you'd burn just lying in bed all day — keeping organs running, regulating temperature, maintaining basic biological function. It accounts for 60–70% of TDEE for most adults.

We support four BMR formulas. The right one depends on what data you have and what population you're part of:

Mifflin-St Jeor (1990) — default

The current standard recommended by the Academy of Nutrition and Dietetics. In published meta-analyses it's generally validated as among the most accurate predictors for the general adult population (ages 19–78). What we use by default.

Note: the female constant is −161, per the original 1990 paper.

Henry / Oxford (2005)

Newer, derived from a much larger dataset (10,552 subjects) than Mifflin's original. Slightly more accurate across diverse populations in recent meta-analyses, and uses different coefficients for different age brackets — so it tracks the metabolic slowdown with age more precisely.

Revised Harris-Benedict (Roza & Shizgal, 1984)

The classic equation everyone knows, updated in 1984 to account for body cell mass measurements. Still in wide use but has been overtaken by Mifflin in clinical practice — Mifflin is consistently more accurate.

Katch-McArdle (1996) — generally most accurate when body fat is known

Uses lean body mass directly. Generally the most accurate option when you have a reliable body composition measurement, because it skips the indirect proxy of weight + height + sex and works straight off the tissue that actually burns calories at rest.

You can switch between any of these under Advanced options in the calculator above.

2Multiplying by activity

BMR alone tells you what a body burns at rest. To get TDEE you multiply by a factor that approximates everything else: walking, working out, fidgeting, digestion. The standard five tiers used industry-wide are 1.2 / 1.375 / 1.55 / 1.725 / 1.9:

These multipliers are practitioner convention — they're not directly from any single peer-reviewed study. They do sit within measured PAL (Physical Activity Level) ranges from doubly-labeled water studies (the gold standard for measuring real-world calorie expenditure), but the discrete five-tier values themselves are eyeballed approximations that have stuck for decades.

We surface the corresponding FAO/WHO PAL classification in the calculator so you can see where your fitness-industry label sits on the scientific scale: FAO/WHO Sedentary covers 1.40–1.69, Moderately Active is 1.70–1.99, and Vigorously Active starts at 2.00. The two scales don't map one-to-one — "Moderately active" at ×1.55, for instance, sits inside the FAO/WHO Sedentary band.

How accurate is the result?

TDEE estimates from any equation-based calculator are typically within ±5–10% of measured values at the individual level. That's why we display a range — a single number implies precision the science doesn't support.

Mifflin-St Jeor specifically predicts BMR within ±10% of indirect-calorimetry measurements in about 82% of non-obese and 70% of obese adults. Once activity multipliers stack on top, error margins compound.

The biggest unmeasured factor is inter-individual NEAT variance — non-exercise activity. Two people identical in size, age, sex, and gym routine can burn 500+ extra calories per day apart purely from how much they move during the rest of the day. No equation captures this directly.