Honest answer: a good TDEE calculator gets most people within ±10% of their true daily burn — roughly ±200–250 kcal for an average adult. For some people the miss is bigger. Anyone promising more precision from four form fields is overselling.
Where the error comes from
Three stacked estimates create the uncertainty. First, BMR formulas like Mifflin-St Jeor are regressions over study populations — accurate to about ±10% for two-thirds of people, worse if your body composition is unusual (very muscular or very lean people should use Katch-McArdle with a body-fat estimate). Second, the activity multiplier is the biggest single error source: most people overestimate their activity by one full level, worth 200–400 kcal/day. Third, the thermic effect of your specific diet varies by a few percent.
How to shrink each error
Use a calculator that splits activity into NEAT (your day) and actual weekly exercise minutes — this site's TDEE calculator does exactly that, because the single “moderately active” dropdown is where estimates go to die. Enter body fat if you know it. And treat the result as a starting hypothesis, not a verdict.
The fix that beats every formula
Track your intake and weight honestly for 2–3 weeks, then back-calculate: average intake minus (weight change × 7,700 kcal/kg ÷ days) is your measured TDEE — adaptation, NEAT quirks and all. The actual TDEE calculator does this arithmetic for you. A formula estimates; a measurement knows.
Frequently asked questions
How far off can a TDEE calculator be?
For about two-thirds of people, within ±10%. For the rest, errors of 300–500 kcal/day are possible — usually from a wrong activity guess or unusual body composition rather than the BMR formula itself.
Which TDEE formula is most accurate?
Mifflin-St Jeor is the best default; Katch-McArdle wins if you know your body fat percentage reasonably well. The difference between formulas is usually smaller than the error in your activity estimate.
Why does every calculator give me a different number?
Different BMR formulas, different activity multiplier definitions, and different rounding. A 100–200 kcal spread between calculators is normal and tells you the precision of the whole exercise.
Is a fitness tracker more accurate than a calculator?
For total daily burn, usually not — wrist trackers commonly miss exercise calories by 20–40%. Two weeks of honest food logging plus the scale beats both.
More guides
- What Is TDEE?
- What Is BMR?
- Mifflin-St Jeor Calculator
- Harris-Benedict Calculator
- Katch-McArdle Calculator
- BMR vs TDEE: What's the Difference?
- What Are MET Values?
- What Is NEAT?
- The Thermic Effect of Food
- Activity Multipliers Explained
- What Is a Calorie?
- Metabolic Adaptation Explained
- The Calorie Deficit, Explained
- 500-Calorie Deficit
- 1,000-Calorie Deficit
- 300-Calorie Deficit
- How Many Calories to Lose 1 Pound a Week
- How Many Calories to Lose 2 Pounds a Week
- Reverse Dieting
- Maintenance Phase
- Calorie Cycling
- Not Losing Weight in a Calorie Deficit? 7 Real Reasons
- Is 1,200 Calories a Day Safe?
- Should You Eat Back Exercise Calories?
- How Long Does Metabolic Adaptation Last?
- Do You Burn Fewer Calories as You Lose Weight?
- Why Your Maintenance Calories Keep Changing
- Calorie Cycling vs Flat Deficit
- How to Avoid Muscle Loss on GLP-1 Medications
Sources
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990. [link]
- Lichtman SW, Pisarska K, Berman ER, et al. Discrepancy between self-reported and actual caloric intake and exercise in obese subjects. N Engl J Med. 1992. [link]
- Pontzer H, Yamada Y, Sagayama H, et al. Daily energy expenditure through the human life course. Science. 2021. [link]