How accurate is the Mifflin-St Jeor equation?

Within 10-15% for most people. The formula assumes average body composition — it overestimates for high-body-fat individuals and underestimates for very lean or muscular people. Track your actual intake vs weight for 2-3 weeks to calibrate.

Why does my TDEE seem too high?

Most people overestimate their activity level. Try one tier lower (e.g., Moderately Active → Lightly Active) and track food intake for 2 weeks. If you are gaining weight at the calculated TDEE, your true maintenance is lower.

What is the difference between TDEE and BMR?

BMR (Basal Metabolic Rate) is the calories your body burns at complete rest — just to keep organs functioning. TDEE multiplies BMR by an activity factor (1.2 for sedentary up to 1.9 for twice-daily training) to estimate total daily burn including movement.

How do I use TDEE to lose weight?

Create a 300-500 calorie daily deficit from your TDEE. This yields roughly 0.5-1 lb per week of loss. Deficits larger than 25% of TDEE accelerate muscle loss and metabolic adaptation — slower is more sustainable.

Should I eat at TDEE on rest days and more on training days?

Either approach works. Eating at TDEE daily (with the correct activity multiplier) is simpler. Carb cycling (more on training days, less on rest days) can improve performance but adds complexity without proven fat-loss advantage for most people.

How often should I recalculate my TDEE?

Recalculate every 4-6 weeks or after any 5 lb change in body weight. TDEE drops as you lose weight — a 10 lb loss typically reduces TDEE by 50-100 calories. This is why calorie targets must decrease during a cut.

Methodology: TDEE Calculator

Scope

Estimates Total Daily Energy Expenditure by computing Mifflin-St Jeor BMR and multiplying by an activity factor between 1.2 (sedentary) and 1.9 (athlete).

TDEE is the daily calorie ledger a nutrition plan is written against. Treat the output as a starting point, not a precise metabolic measurement.

Formula

BMR (men) = 10*weight_kg + 6.25*height_cm - 5*age + 5. BMR (women) = 10*weight_kg + 6.25*height_cm - 5*age - 161. TDEE = BMR x activity_factor.

Coefficients

Parameter	Value	Note
Weight coefficient	`10 kcal/kg`
Height coefficient	`6.25 kcal/cm`
Age coefficient	`-5 kcal/year`
Sex constant (male / female)	`+5 / -161`
Activity factor — sedentary	`1.2`
Activity factor — light	`1.375`
Activity factor — moderate	`1.55`
Activity factor — very active	`1.725`
Activity factor — athlete	`1.9`

Data sources

Mifflin MD, St Jeor ST, Hill LA, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247. — PMID 2305711. The most accurate of the common BMR predictors for non-obese adults.
Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005;105(5):775-789. — PMID 15883556. Meta-analysis identifying Mifflin-St Jeor as the most accurate predictor.
Pontzer H, Yamada Y, Sagayama H, et al. Daily energy expenditure through the human life course. Science. 2021;373(6556):808-812. — PMID 34385400. Multi-country doubly-labeled-water dataset used to validate the activity-factor bands.

Assumptions

User inputs metric or imperial units correctly; the tool converts internally.
Chosen activity factor matches real-world training and occupational load; 'moderate' regularly over-states true activity for office workers who lift 3x/week.
Lean-mass differences between individuals are not adjusted for (Katch-McArdle is a separate path).

Approximation range

Mifflin-St Jeor RMSE vs indirect calorimetry is typically 150–200 kcal/day for healthy non-obese adults. For obese populations the error widens and Katch-McArdle or DXA-derived LBM performs better.

Activity factors are bucketed; real daily expenditure often falls between two buckets, giving an inherent +/- 10% band.

Limitations

Does not model NEAT adaptations during large deficits, which can shave 10–20% off predicted expenditure within weeks.
Single-point estimate — does not track week-to-week weight trend that a calibrated nutrition plan should use.
Ignores thyroid status, medications, and pregnancy.

Reproducibility

Male, 85 kg, 180 cm, 30 yrs, moderate activity: BMR = 10*85 + 6.25*180 - 5*30 + 5 = 1830 kcal. TDEE = 1830 * 1.55 = 2836 kcal.

Change log

2026-04-24: methodology page first published.

BMR Calculator — Estimate basal metabolic rate and maintenance calories using Mifflin-St Jeor assumptions.
Macro Calculator — Convert calorie targets into protein, carbs, and fat grams for your goal.
Protein Intake Calculator — Get daily protein targets based on training level and goal.
Water Intake Calculator — Calculate daily water intake based on weight, activity level, and climate.

Worked example

Computed by the same engine bundle served at /engines/tdee-calculator.js. Re-runnable: the values below are the literal output of compute(engineInput).

Input

tool: tdee_calculator
sex: male
age: 30
weight_kg: 80
height_cm: 178
activity_level: moderate

Output

bmr: 1767.5
tdee: 2739.625
activityFactor: 1.55

FAQ

How accurate is the Mifflin-St Jeor equation?: Within 10-15% for most people. The formula assumes average body composition — it overestimates for high-body-fat individuals and underestimates for very lean or muscular people. Track your actual intake vs weight for 2-3 weeks to calibrate.
Why does my TDEE seem too high?: Most people overestimate their activity level. Try one tier lower (e.g., Moderately Active → Lightly Active) and track food intake for 2 weeks. If you are gaining weight at the calculated TDEE, your true maintenance is lower.
What is the difference between TDEE and BMR?: BMR (Basal Metabolic Rate) is the calories your body burns at complete rest — just to keep organs functioning. TDEE multiplies BMR by an activity factor (1.2 for sedentary up to 1.9 for twice-daily training) to estimate total daily burn including movement.
How do I use TDEE to lose weight?: Create a 300-500 calorie daily deficit from your TDEE. This yields roughly 0.5-1 lb per week of loss. Deficits larger than 25% of TDEE accelerate muscle loss and metabolic adaptation — slower is more sustainable.
Should I eat at TDEE on rest days and more on training days?: Either approach works. Eating at TDEE daily (with the correct activity multiplier) is simpler. Carb cycling (more on training days, less on rest days) can improve performance but adds complexity without proven fat-loss advantage for most people.
How often should I recalculate my TDEE?: Recalculate every 4-6 weeks or after any 5 lb change in body weight. TDEE drops as you lose weight — a 10 lb loss typically reduces TDEE by 50-100 calories. This is why calorie targets must decrease during a cut.