Most TDEE calculators online still use the Harris-Benedict equation, first published in 1919 and revised in 1984. That equation systematically overestimates basal metabolic rate by 5 to 15 percent in modern adults, according to the 2005 systematic review by Frankenfield and colleagues in the Journal of the American Dietetic Association. Use Harris-Benedict and your maintenance calorie estimate is too high. Use it to set a deficit and the deficit is smaller than you think.
This calculator defaults to the Mifflin-St Jeor equation (1990), which the same review identified as the most accurate of any tested predictive equation. It also offers a Katch-McArdle option for athletes and lean populations where body fat is known and the standard equation underestimates lean tissue contribution to BMR.
How this calculator works
Every multiplier and constant in the calculator comes from a primary source. There are no made-up numbers.
- BMR (default): Mifflin et al. 1990 in the American Journal of Clinical Nutrition. For men: BMR = 10w + 6.25h - 5a + 5. For women: BMR = 10w + 6.25h - 5a - 161 (weight in kg, height in cm, age in years). Validated as the most accurate predictive equation by the Frankenfield et al. 2005 systematic review of every major BMR formula against indirect calorimetry.
- BMR (Katch-McArdle option): when you provide a body fat percentage, the calculator switches to BMR = 370 + 21.6 × LBM, where LBM is lean body mass in kg. The equation is from Katch and McArdle's 1996 textbook Introduction to Nutrition, Exercise, and Health. It is more accurate for very lean and athletic populations because BMR scales tightly to lean tissue, not total body weight.
- Activity multipliers: 1.2 (sedentary), 1.375 (light), 1.55 (moderate), 1.725 (very active), 1.9 (extra active). These are the standard multipliers introduced in the original Mifflin et al. 1990 paper and used in essentially every clinical and research application of the equation since.
- Cut target: 20 percent below TDEE. Helms et al. 2014, in their review of natural bodybuilding contest preparation in the Journal of the International Society of Sports Nutrition, recommend not exceeding a 25 percent deficit for sustained periods to preserve lean mass and prevent excessive metabolic adaptation.
- Lean bulk target: 12 percent above TDEE. Based on Slater et al. 2019 in Frontiers in Nutrition, who concluded that a small surplus of 10 to 20 percent above maintenance is sufficient to support maximal muscle protein synthesis in resistance-trained adults. Larger surpluses produce more weight gain but disproportionately more fat.
BMR vs TDEE: what the difference means
Basal metabolic rate is the calorie cost of being alive: keeping your heart beating, lungs breathing, brain firing, and core temperature stable while you do nothing. It accounts for about 60 to 75 percent of total daily energy expenditure for most adults. The remaining 25 to 40 percent is the thermic effect of food (roughly 10 percent), structured exercise (variable), and nonexercise activity thermogenesis or NEAT (highly variable).
NEAT is everything you do that is not deliberate exercise: walking to the kitchen, fidgeting, standing up, taking the stairs. Levine 2004 in the American Journal of Physiology showed that NEAT can vary by up to 2,000 calories per day between two adults of the same size. That is the single biggest reason TDEE estimates miss: the activity multiplier collapses a hugely variable NEAT contribution into a single number.
Worked examples (for quick reference)
Here are seven common scenarios with the calculator output, so you can sanity-check the tool against your own profile.
| Person | Activity | BMR | TDEE |
|---|---|---|---|
| 30 y male, 165 lb, 5 ft 9 in75 kg, 175 cm | Moderate (1.55) | 1,699 kcal | 2,633 kcal |
| 25 y female, 132 lb, 5 ft 5 in60 kg, 165 cm | Light (1.375) | 1,345 kcal | 1,850 kcal |
| 40 y male, 187 lb, 5 ft 11 in85 kg, 180 cm | Very active (1.725) | 1,780 kcal | 3,071 kcal |
| 35 y female, 154 lb, 5 ft 6 in70 kg, 168 cm | Sedentary (1.2) | 1,414 kcal | 1,697 kcal |
| 50 y male, 198 lb, 5 ft 10 in90 kg, 178 cm | Moderate (1.55) | 1,768 kcal | 2,740 kcal |
| 28 y female, 143 lb, 5 ft 7 in65 kg, 170 cm | Very active (1.725) | 1,412 kcal | 2,435 kcal |
| 65 y male, 172 lb78 kg, 22% BF (Katch-McArdle) | Light (1.375) | 1,684 kcal | 2,316 kcal |
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If you're cutting
The calculator's default cut target is TDEE minus 20 percent. For most adults that produces a deficit of 400 to 600 calories per day, which translates to roughly 0.5 to 0.75 kg (1 to 1.5 lb) of weight loss per week. The Helms et al. 2014 review on natural bodybuilding nutrition recommends not exceeding a 25 percent deficit for sustained periods. Larger deficits accelerate the loss of lean mass, magnify metabolic adaptation, and crush adherence.
Pair the deficit with adequate protein. The protein calculator sets a defensible target. Higher protein during a deficit (around 2.0 to 2.4 g/kg of body weight per day) preserves lean mass and improves satiety. We unpacked the science in the piece on body recomposition.
If you're maintaining
Maintenance is your TDEE itself. It is also where most adults should spend most of their time. Body recomposition (gaining muscle while losing fat) happens most reliably at or very close to maintenance, particularly in untrained or detrained individuals returning to consistent resistance training. The ISSN position stand on diets and body composition (Aragon et al. 2017) in the Journal of the International Society of Sports Nutrition covers the evidence in depth.
If you're bulking
The calculator defaults to a 12 percent surplus, which lands inside the 10 to 20 percent window Slater et al. 2019 identified as sufficient for maximal muscle protein synthesis in trained adults. A 12 percent surplus on a 2,500 calorie maintenance is about 300 extra calories per day, producing roughly 0.25 to 0.5 kg (0.5 to 1 lb) of bodyweight gain per week. Faster gains are mostly fat. Slower or no gain means the surplus is too small for your actual TDEE.
Three myths the calculator deliberately ignores
Myth 1: a calorie deficit always produces fat loss
It does, on average and over time. But the body adapts. Hall et al. 2012 in the American Journal of Clinical Nutrition showed that as you lose weight, both BMR and NEAT drop, narrowing the deficit you started with. The implication: a static calorie target works for a while, then stalls. Recalculate every 4 to 6 kg of weight change. Treat the calculator's number as a starting point, not a permanent prescription.
Myth 2: women have much lower BMR than men
Per kilogram of lean mass, the difference is small. Most of the gap in absolute BMR between same-sized men and women comes from body composition: men typically carry more lean mass at the same total weight. The Mifflin-St Jeor sex constants (+5 for men, -161 for women) account for this average difference, but the Katch-McArdle equation, which scales BMR directly to lean body mass, is sex-neutral. If you switch to Katch-McArdle with an accurate body fat measurement, the male-female gap shrinks substantially.
Myth 3: metabolism slows dramatically after 30
The age coefficient in Mifflin-St Jeor is 5 calories per year, which means a 50-year-old has a BMR about 100 calories lower than a 30-year-old of the same height and weight. That is real but small. The much larger driver of midlife weight gain is loss of muscle mass and a drop in NEAT. Resistance training that preserves lean mass largely offsets the BMR decline. Aging slows metabolism less than most adults assume; sedentary aging slows it a lot.
When to ignore this calculator
The calculator is built for healthy adults using common goal categories. A few situations require professional input rather than a generic tool.
- Pregnancy and lactation. Energy needs rise during the second and third trimesters and during lactation. Defer to your obstetric care team for individualized targets.
- Hyperthyroidism or hypothyroidism. Thyroid disease meaningfully shifts BMR in either direction. Work with an endocrinologist; predictive equations are unreliable here.
- Eating disorders or recent recovery. A registered dietitian who specializes in eating disorders is a better fit than any generic calculator.
- Post-bariatric surgery. BMR after sleeve gastrectomy, gastric bypass, or related procedures often deviates from predicted values for years. Use indirect calorimetry if available, or work with the surgical nutrition team.
- Very high BMI (above 40). Mifflin-St Jeor systematically underestimates BMR in class-3 obesity. Frankenfield et al. 2003 recommend using measured BMR via indirect calorimetry rather than predictive equations in this group.
- Older adults (65+). Mifflin-St Jeor remains valid but slightly underestimates BMR in some older adults. Treat the calculator output as a floor; recalibrate if weight does not move as predicted.
For everyone else, the calculator gives a defensible starting point. Hold the target for two to three weeks, weigh yourself daily, average the readings weekly, and adjust by 100 to 200 calories if the trend does not match the goal.
Related reading
References
- 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;51(2):241-247. doi:10.1093/ajcn/51.2.241
- 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. doi:10.1016/j.jada.2005.02.005
- Katch FI, McArdle WD. Introduction to Nutrition, Exercise, and Health. 4th ed. Philadelphia: Lea and Febiger; 1996.
- Levine JA. "Nonexercise activity thermogenesis (NEAT): environment and biology." Am J Physiol Endocrinol Metab. 2004;286(5):E675-E685. doi:10.1152/ajpendo.00562.2003
- Helms ER, Aragon AA, Fitschen PJ. "Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation." J Int Soc Sports Nutr. 2014;11:20. doi:10.1186/1550-2783-11-20
- Slater GJ, Dieter BP, Marsh DJ, Helms ER, Shaw G, Iraki J. "Is an energy surplus required to maximize skeletal muscle hypertrophy associated with resistance training?" Front Nutr. 2019;6:131. doi:10.3389/fnut.2019.00131
- Aragon AA, Schoenfeld BJ, Wildman R, et al. "International Society of Sports Nutrition Position Stand: diets and body composition." J Int Soc Sports Nutr. 2017;14:16. doi:10.1186/s12970-017-0174-y
- Frankenfield DC, Rowe WA, Smith JS, Cooney RN. "Validation of several established equations for resting metabolic rate in obese and nonobese people." J Am Diet Assoc. 2003;103(9):1152-1159. doi:10.1016/s0002-8223(03)00982-9
- Hall KD, Heymsfield SB, Kemnitz JW, Klein S, Schoeller DA, Speakman JR. "Energy balance and its components: implications for body weight regulation." Am J Clin Nutr. 2012;95(4):989-994. doi:10.3945/ajcn.112.036350
Frequently Asked Questions
What is TDEE and how is it calculated?
TDEE stands for total daily energy expenditure, the total number of calories your body burns in a day. It is calculated by multiplying your basal metabolic rate (BMR) by an activity multiplier between 1.2 and 1.9. The Mifflin-St Jeor equation (1990) is the most accurate predictive BMR formula across populations, according to a 2005 systematic review by Frankenfield and colleagues in the Journal of the American Dietetic Association. For a 30-year-old male, 75 kg, 175 cm, with moderate activity, TDEE is approximately 2,633 calories per day.
Which BMR equation is most accurate?
Frankenfield and colleagues (2005) reviewed every major BMR equation against indirect calorimetry across both lean and obese populations. Mifflin-St Jeor was accurate within 10 percent of measured BMR in 82 percent of nonobese and 70 percent of obese subjects, the highest accuracy of any tested equation. Harris-Benedict overestimated by 5 to 15 percent on average. For lean and athletic populations specifically, the Katch-McArdle equation can be more accurate because it scales to lean body mass rather than total body weight, but it requires a reliable body fat measurement.
How accurate is a TDEE calculator?
Mifflin-St Jeor predicts BMR within roughly 10 percent of measured values for most healthy adults. The bigger source of error is the activity multiplier. Levine (2004) showed that nonexercise activity thermogenesis (NEAT) varies by up to 2,000 calories per day between individuals of similar size, meaning the activity multiplier introduces 10 to 20 percent uncertainty into your TDEE estimate. Use the calculator as a starting point, then adjust based on two to four weeks of weight tracking.
What is a safe calorie deficit for fat loss?
A 20 percent deficit below TDEE is the standard recommendation for sustainable fat loss while preserving lean mass. Helms and colleagues (2014), in their review of natural bodybuilding contest preparation, recommend not exceeding a 25 percent deficit for sustained periods because larger deficits accelerate the loss of fat-free mass and slow metabolic adaptation. For a 2,500 calorie maintenance, that means a target of about 2,000 calories per day, producing roughly 0.5 to 0.75 kg (1 to 1.5 lb) of weight loss per week.
How much of a calorie surplus do I need to build muscle?
Slater and colleagues (2019), in a review published in Frontiers in Nutrition, concluded that a small surplus of about 10 to 20 percent above maintenance is sufficient to support maximal muscle protein synthesis in resistance-trained individuals. Larger surpluses produce more weight gain but disproportionately more fat. The calculator defaults to a 12 percent surplus for the lean-bulk target. For a 2,500 calorie maintenance, that means about 2,800 calories per day, producing roughly 0.25 to 0.5 kg (0.5 to 1 lb) of bodyweight gain per week.
Should I trust the very active or extra active multiplier?
These multipliers (1.725 and 1.9) are the most error-prone in the entire calculation. They assume two or more hours of structured exercise per day, plus a physically demanding job. Most people who select them are overestimating their activity. If you select very active or extra active and your weight does not move as predicted after two to three weeks at the calculated TDEE, drop one tier and recalculate. NEAT differences (Levine 2004) explain most of the gap.
When should I use Katch-McArdle instead of Mifflin-St Jeor?
Use Katch-McArdle when you have a reliable body fat measurement (DEXA scan, BodPod, or repeated skinfolds by a trained tester) and your body composition is meaningfully different from the average adult Mifflin-St Jeor was built on. That includes very lean athletes, bodybuilders, and people with significantly above-average muscle mass. For most adults at typical body fat levels (15 to 30 percent men, 22 to 38 percent women), Mifflin-St Jeor and Katch-McArdle return similar BMRs and the simpler equation is fine.