Mifflin-St Jeor TDEE Calculator
Total Daily Energy Expenditure (TDEE) is the total calories your body burns in a 24-hour period — it's your Basal Metabolic Rate (BMR) multiplied by an activity multiplier that accounts for movement, exercise, and digestion. TDEE is the single most important number for anyone planning a cut, lean bulk, or maintenance phase: eat below it and you lose weight, eat above it and you gain. The Mifflin-St Jeor equation (developed at the University of Nevada School of Medicine, Reno, in 1990) is the formula the Academy of Nutrition and Dietetics explicitly recommends as the most accurate for non-obese and obese adults — outperforming Harris-Benedict (1919) by roughly 5% per NIH validation studies. Your TDEE breaks down into four components: BMR (~60–70% of total — the calories you burn just being alive), Thermic Effect of Food (TEF) (~10% — energy spent digesting), Non-Exercise Activity Thermogenesis (NEAT) (15–30% — fidgeting, walking, posture), and Exercise Activity Thermogenesis (EAT) (0–30% — intentional training). Understanding these components is why two people with identical BMRs can have wildly different TDEEs depending on their job, training, and daily movement habits. This calculator uses lbs, inches, age, sex, and activity level to give you the baseline calorie number every evidence-based nutrition coach starts with.
Total Daily Energy Expenditure (TDEE) is your BMR multiplied by an activity factor: sedentary 1.2, light 1.375, moderate 1.55, very active 1.725, extra 1.9. Using Mifflin-St Jeor, a 30-year-old, 70 kg, 175 cm sedentary man has BMR of 1,649 kcal and TDEE of about 1,978 kcal/day. USDA dietary guidelines suggest 2,000-3,000 kcal/day for adult men and 1,600-2,400 for adult women, depending on activity.
When to use this calculator
- Cutting phase for visible abs: set a 500 kcal/day deficit (≈ 1 lb/week fat loss) from your maintenance TDEE without dropping below your BMR.
- Lean bulk: add a 200–500 kcal surplus over TDEE to gain muscle while minimizing fat gain (target ~0.25–0.5 lb/week scale gain).
- Maintenance check: validate whether your current intake actually matches your true energy needs after a body recomposition phase.
- Calibrate your fitness tracker (Apple Watch, Fitbit, Garmin, Whoop): trackers commonly overestimate active calories by 15–30% — compare against Mifflin-St Jeor TDEE as a sanity check.
- Reverse dieting back to maintenance: rebuild metabolic capacity after a long cut by stepping intake up toward calculated TDEE in 50–100 kcal weekly increments.
- Macro planning: split TDEE into protein (0.8–1.0 g per lb bodyweight), fat (0.3–0.4 g/lb), and remaining calories from carbs.
Example: 30-year-old male, 154 lb (70 kg), 5'9" (175 cm), sedentary
- BMR (Mifflin-St Jeor): 10×70 + 6.25×175 − 5×30 + 5 = 1,649 kcal
- Sedentary multiplier: × 1.2
- TDEE = 1,649 × 1.2 ≈ 1,978 kcal/day
How it works
3 min readThe Mifflin-St Jeor Equation (1990)
The formula is sex-specific because lean body mass (the main BMR driver) differs between men and women:
The equation outputs resting calories per day. The Academy of Nutrition and Dietetics (AND) Evidence Analysis Library lists Mifflin-St Jeor as the most accurate predictive equation for resting metabolic rate in both non-obese (BMI < 30) and obese (BMI ≥ 30) US adults — accurate within ±10% in roughly 80% of cases versus indirect calorimetry.
Converting US Units (lbs and inches) to Metric
The equation needs kg and cm. The conversions are:
Activity Multipliers — Be Honest, Most People Overestimate
Multiply BMR by your activity factor to get TDEE. These are the standard Mifflin-St Jeor multipliers:
| Level | Multiplier | Real-world definition |
|---|---|---|
| Sedentary | 1.2 | Desk job, no structured exercise, < 5,000 steps/day |
| Lightly active | 1.375 | Light exercise 1–3 days/week, or job with some walking |
| Moderately active | 1.55 | Moderate exercise 3–5 days/week (gym 4×/week + 8k steps) |
| Very active | 1.725 | Hard exercise 6–7 days/week, training 60–90 min daily |
| Extra active | 1.9 | Very hard training + physical job, or two-a-day athletes |
Pitfall: sitting at a desk all day and lifting 3×/week is Lightly Active (1.375), not Moderate. Research (Levine et al., Mayo Clinic NEAT studies) shows the gym session itself adds only ~250–400 kcal — the rest of the day still drives the multiplier.
Worked Example (US Units)
A 30-year-old man, 180 lb (81.6 kg), 5'10" (177.8 cm), sedentary desk worker:
1. BMR = 10(81.6) + 6.25(177.8) − 5(30) + 5
2. BMR = 816 + 1,111 − 150 + 5 = 1,782 kcal/day (resting)
3. TDEE = 1,782 × 1.2 = ~2,138 kcal/day
If the same man trains hard 4×/week and walks 10k steps daily, his multiplier jumps to 1.55, giving TDEE ≈ 2,762 kcal/day — a 600 kcal swing from activity alone.
Cutting: How Aggressive Is Safe?
A 500 kcal/day deficit equals roughly 1 lb/week of fat loss (3,500 kcal ≈ 1 lb of fat). Cap the deficit at ~1% of bodyweight per week — a 200 lb man can lose ~2 lb/week sustainably, while a 140 lb woman should target ~1.4 lb/week max. Beyond that, muscle loss accelerates and adherence collapses. Never sustain intake below your BMR for more than short refeed-broken periods — it tanks thyroid output (T3), drops testosterone, and induces strong adaptive thermogenesis.
Bulking: Surplus Math
For lean gainers, 200–500 kcal surplus over TDEE supports ~0.25–0.5 lb/week scale gain. Above that, the body's nutrient partitioning shifts toward fat storage — extra calories don't build extra muscle past a ceiling of ~0.5 lb/week for natural trainees (per ISSN position stand on bodybuilding, Helms et al., 2014).
Why TDEE Drops During a Cut (Metabolic Adaptation)
As you lose weight, NEAT decreases: you fidget less, walk slower, take fewer non-purposeful steps. Smith et al. (2021, Obesity) documented NEAT drops of 100–300 kcal/day during sustained deficits, independent of body mass loss. This is why static TDEE calculators always overestimate after 4–6 weeks of dieting — recalculate every 10 lb lost or every 4 weeks, whichever comes first.
LBM-Based Equations (Katch-McArdle) — When Mifflin Misleads
Mifflin-St Jeor uses total bodyweight, which treats a 200 lb lean lifter the same as a 200 lb sedentary individual at the same height/age — they're not equivalent. If you have a recent DEXA, BodPod, or accurate caliper read, Katch-McArdle (BMR = 370 + 21.6 × LBM in kg) is more accurate for lean, muscular individuals. For everyone else, Mifflin-St Jeor remains the AND-recommended starting point.
Frequently asked questions
How accurate is the Mifflin-St Jeor TDEE calculator?
BMR estimates are accurate within ±10% in roughly 80% of healthy adults compared to indirect calorimetry (the gold standard), per the Academy of Nutrition and Dietetics Evidence Analysis Library. The TDEE multiplier introduces additional variance — most people misjudge their activity level, which is the biggest error source. Treat the number as a 2-week starting point, then adjust based on actual scale and tape-measure trends.
Why am I not losing weight even though I'm eating at a deficit?
Three common culprits: (1) underreported intake — most people undercount calories by 20–40% (Lichtman et al., NEJM 1992 — still replicated). Weigh foods for 2 weeks to recalibrate. (2) overestimated activity multiplier — sitting at a desk plus 3 gym sessions is Lightly Active (1.375), not Moderate. (3) metabolic adaptation — after 4+ weeks of deficit, NEAT drops 100–300 kcal/day. Recalculate TDEE every 10 lb lost or take a 1–2 week diet break at maintenance.
Does the activity multiplier overestimate my real calorie burn?
Almost always, yes — for most adults the standard multipliers run high by 10–20%. The 1.55 'Moderately Active' tier assumes 3–5 quality training days plus elevated daily movement (8k+ steps), not just gym time. If you have a desk job and lift 3×/week with low daily steps, you're closer to 1.375. Wearable trackers also overestimate active calories by 15–30% (Stanford study, Shcherbina et al., 2017) — don't double-count by adding tracker burns on top of a high multiplier.
Is it safe to eat below my BMR while cutting?
Short-term (a few weeks in an aggressive cut for a contest or photoshoot), it's tolerable for healthy adults under supervision. Long-term, no — sustained sub-BMR intake drops T3 thyroid output, suppresses sex hormones, accelerates lean mass loss, and triggers adaptive thermogenesis (your maintenance keeps falling). The general guideline: keep deficits between 15–25% below TDEE and never let intake drop below 1,200 kcal for women or 1,500 kcal for men without medical supervision.
I sit at a desk all day but train 3x/week — am I Sedentary or Lightly Active?
Lightly Active (1.375). Sedentary (1.2) assumes virtually no structured exercise. Three lifting sessions per week add ~750–1,200 kcal over the week — that lines up with the bump from 1.2 to 1.375. If you also walk 8,000+ steps daily on non-training days, you can justify Moderately Active (1.55). Be honest about the rest of your day, not just your workouts.
What is reverse dieting and when should I do it?
Reverse dieting is a gradual return to maintenance calories after a cut — typically +50 to +100 kcal/week — to rebuild metabolic capacity without rebounding into fat gain. Use it when you've been in a deficit 12+ weeks, hit a plateau at very low intake, or finished a competition prep. It works because NEAT and TEF recover with feeding, and you avoid the binge-overshoot trap of jumping straight back to TDEE.
Does my TDEE drop as I lose weight on a deficit?
Yes — for two reasons. First, mechanically: a smaller body burns fewer calories per day (BMR scales with mass). Second, adaptively: prolonged deficits suppress NEAT, lower T3, and reduce TEF. Smith et al. (2021, Obesity) measured 100–300 kcal/day adaptive drops that persist past the cut. Practical fix: recalculate TDEE every 10 lb lost, and plan refeed days or 1-week maintenance breaks every 6–8 weeks.
How is Mifflin-St Jeor different from Harris-Benedict or Katch-McArdle?
Harris-Benedict (1919) was built on a small early-20th-century sample and overestimates BMR by ~5% in modern adults — that's why the Academy of Nutrition and Dietetics switched its recommendation to Mifflin-St Jeor (1990). Katch-McArdle uses lean body mass instead of total bodyweight, so it's more accurate for lean, muscular individuals if you have a reliable DEXA or BodPod number. For the general population without LBM data, Mifflin-St Jeor is the most accurate equation available.
Should I use TDEE for setting macros?
Yes — TDEE sets the total kcal ceiling, then split into macros: protein at 0.8–1.0 g per lb of bodyweight (ISSN position stand, Jäger et al., 2017), fat at 0.3–0.4 g/lb (minimum ~20% of calories for hormonal health), and remaining calories from carbs. For a 180 lb male at 2,138 TDEE cutting to 1,638: 180 g protein (720 kcal), 60 g fat (540 kcal), 95 g carbs (380 kcal).
Sources and 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.
- Academy of Nutrition and Dietetics — Evidence Analysis Library: Measuring RMR (Mifflin-St Jeor recommended equation)
- Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition Position Stand: Protein and Exercise. J Int Soc Sports Nutr. 2017;14:20.
- 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.
- ACSM's Guidelines for Exercise Testing and Prescription, 11th ed. American College of Sports Medicine.
- Smith RL, Soeters MR, Wüst RCI, Houtkooper RH. Metabolic Flexibility as an Adaptation to Energy Resources and Requirements in Health and Disease. Endocr Rev. 2018;39(4):489-517.
- USDA Dietary Guidelines for Americans 2020-2025
- NIH NIDDK — Body Weight Planner