How the Calculation Works
This calculator uses the Mifflin-St Jeor equation to estimate your resting metabolic rate (RMR), then multiplies it by an activity factor to get your TDEE. Mifflin-St Jeor consistently outperforms older formulas like Harris-Benedict in modern validation studies, especially for people who are not extremely lean or heavy.
Activity Multiplier Reference Table
TDEE is your resting metabolic rate (RMR) multiplied by an activity factor. The table below shows how each level scales a sample 1,800 kcal RMR, so you can see roughly how much a change in activity level moves your own number.
| Level | Multiplier | Description | Worked example |
|---|---|---|---|
| Sedentary | 1.2 | Desk job, little to no structured exercise | 1,800 kcal RMR × 1.2 = 2,160 kcal TDEE |
| Light | 1.375 | Exercise 1 to 3 days a week | 1,800 kcal RMR × 1.375 = 2,475 kcal TDEE |
| Moderate | 1.55 | Exercise 3 to 5 days a week | 1,800 kcal RMR × 1.55 = 2,790 kcal TDEE |
| Active | 1.725 | Exercise 6 to 7 days a week | 1,800 kcal RMR × 1.725 = 3,105 kcal TDEE |
| Very active | 1.9 | Hard daily training or a physically demanding job | 1,800 kcal RMR × 1.9 = 3,420 kcal TDEE |
Most people overestimate their own activity level by one tier, especially once a desk job is factored in around workouts. If your weight isn't tracking the way the calculator predicts, try the level below what you first picked before assuming the formula itself is wrong.
Calorie Calculator to Lose Weight: Setting Your Deficit
Once you have your TDEE, losing weight is a matter of eating consistently below it. A 300 to 500 calorie daily deficit loses roughly 0.5 to 1 pound (0.2 to 0.5 kg) a week while giving your body enough fuel to preserve muscle during training. The Fat Loss (moderate) row above applies a 500 calorie deficit automatically; the Fat Loss (aggressive) row applies 750 for a faster rate that demands more consistency with protein and training to protect muscle.
Avoid deficits larger than 750 to 1,000 calories unless you're working with a coach or clinician. Beyond that point, muscle loss accelerates, energy for training drops, and the diet becomes harder to sustain long enough to reach your goal.
TDEE vs BMR vs RMR
These three terms get used almost interchangeably, but they measure slightly different things. BMR (Basal Metabolic Rate) is the calories your body burns at complete rest, measured under strict lab conditions. RMR (Resting Metabolic Rate) is a more practical, slightly higher estimate of the same idea, measured under normal resting conditions, and it's what this calculator's underlying formula produces. TDEE (Total Daily Energy Expenditure) takes that resting number and multiplies it by an activity factor to account for exercise, daily movement, and digestion, giving you the number that actually matters for setting a calorie target.
In practice, RMR and BMR are close enough that the distinction rarely changes a real-world calorie target. TDEE is the number to actually eat to, since it's the only one of the three that accounts for how active you are.
The Katch-McArdle Lean Mass Path
Mifflin-St Jeor estimates RMR from your total weight, height, age, and sex, which works well for an average body composition at a given weight. It can misjudge two people who weigh the same but carry very different amounts of muscle. If you have a reasonably reliable body fat reading, from calipers, a DEXA scan, or a bioelectrical impedance scale used the same way each time, enter it above to switch the calculator to the Katch-McArdle formula instead.
Katch-McArdle first strips out fat mass to find your lean body mass (LBM), then estimates RMR directly from that: RMR = 370 + (21.6 × LBM in kg). A 90 kg person at 15% body fat has 76.5 kg of lean mass, giving an RMR of 370 + (21.6 × 76.5) = 2,020 kcal, noticeably different from what a weight-only formula would predict for the same 90 kg. This matters most for lifters who are leaner or more muscular than average, where lean mass, not total weight, is the better predictor of resting energy burn.
A rough or outdated body fat estimate produces a worse result than leaving the field blank. If your only reading is a bathroom scale's impedance guess taken once, Mifflin-St Jeor from your actual weight and height is usually the more reliable starting point.
Worked Recalculation Protocol
Run this exact sequence every 2 to 3 weeks to keep your target accurate as your weight changes. Assume a 30-year-old male, 90 kg, 175 cm, moderate activity, targeting fat loss.
Step 1, baseline: RMR = (10 × 90) + (6.25 × 175) − (5 × 30) + 5 = 1,831 kcal. TDEE = 1,831 × 1.55 = 2,838 kcal. Target at a 500 kcal deficit = 2,338 kcal/day.
Step 2, log and weigh: Eat 2,338 kcal/day for 2 to 3 weeks, weighing yourself each morning under the same conditions, and average the week rather than reacting to a single day's number.
Step 3, compare the trend to the prediction: A 500 kcal daily deficit predicts roughly 0.45 kg (1 lb) of loss per week, so 2 to 3 weeks should show 0.9 to 1.4 kg down. If the average weekly loss came in at 0.3 kg instead, your real deficit is smaller than the formula assumed.
Step 4, recalculate the target, not the formula: Do not re-run Mifflin-St Jeor with a new weight input and expect it to fix the gap, the equation was already an estimate and the gap is the correction data you actually needed. Instead, subtract roughly 150 to 200 kcal from your current intake and hold the new number for another 2 to 3 weeks before reassessing again.
Correcting Your Activity Multiplier From Measured Results
The activity multiplier (1.2 to 1.9) is the least precise part of the formula because it is a category estimate, not a measurement of you specifically. After 2 to 3 weeks of consistent logging and weigh-ins, you can back-calculate your true multiplier directly from what actually happened.
Take the example above: eating 2,338 kcal/day produced only 0.3 kg of loss over 2 weeks (about 1,050 kcal of true weekly deficit, versus the 3,500 kcal predicted by a 500 kcal/day target). That gap of roughly 2,450 kcal/week, about 350 kcal/day, means your real TDEE was closer to 2,338 + 350 = 2,688 kcal, not the 2,838 kcal the moderate-activity multiplier predicted. Dividing that measured TDEE by your RMR (2,688 ÷ 1,831 = 1.47) gives your corrected personal multiplier, closer to Light than Moderate.
Use that corrected multiplier for every future recalculation instead of re-guessing your activity tier from the description text. It accounts for your specific daily movement, workout intensity, and any overestimation in the original self-reported activity level, all in one number.
Why Your Real TDEE Differs From the Estimate
The Mifflin-St Jeor equation this calculator uses is the most accurate predictive formula available in research, but "most accurate" still means predictions can be off by 10 to 15% for any individual, since genetics, muscle mass, sleep, and hormonal factors all affect metabolic rate in ways a formula based on age, weight, height, and sex can't capture directly.
That's why the number above is a starting point, not a fixed truth. Eat at your calculated target for 2 to 3 weeks and track your weight trend, not day-to-day fluctuations. If the scale isn't moving the direction your goal requires, adjust your intake by 100 to 200 calories and reassess. Your actual, observed TDEE, based on what happens when you eat a known number of calories, is always more reliable than any formula's estimate. See the TDEE glossary entry for how the number itself is calculated.
Pair whichever target you pick with adequate protein (roughly 1.6 to 2.2g per kg of bodyweight) so the calories go toward the outcome you actually want, not just the scale. If you're building a full training plan around this number, see our 3 day full body plan for beginners or the AI workout plan vs personal trainer comparison to see how adaptive programming handles nutrition alongside training. For the muscle-building side of the equation, see our protein calculator, the macros glossary entry, and our one-rep max calculator to track strength alongside body composition.
Frequently Asked Questions
- What is TDEE?
- Total Daily Energy Expenditure: the total calories your body burns in a day, including your resting metabolic rate, digestion, and all activity. Eating at your TDEE maintains your current weight.
- How many calories should I eat to lose weight?
- A deficit of 300 to 500 calories below TDEE loses roughly 0.5 to 1 pound (0.2 to 0.5 kg) a week while preserving muscle, provided protein and training stay consistent. Bigger deficits speed weight loss but increase muscle loss risk.
- How many calories should I eat to build muscle?
- A surplus of 200 to 300 calories above TDEE supports muscle growth without excessive fat gain. Beginners can often build muscle at maintenance or a small surplus; more advanced lifters need a larger surplus for continued gains.
- Is this calculator accurate?
- It uses the Mifflin-St Jeor equation, the most accurate predictive formula in research for estimating resting metabolic rate. Real-world TDEE still varies by 10 to 15% between individuals, so treat the result as a starting point and adjust based on 2 to 3 weeks of actual weight trend data.
- What's the best calorie calculator to lose weight?
- The best calorie calculator to lose weight is one that starts from your real TDEE, not a generic estimate, then applies a moderate deficit. This calculator does both: enter your stats above and use the Fat Loss (moderate) row for a sustainable 300 to 500 calorie daily deficit, or Fat Loss (aggressive) if you want to move faster and can tolerate a higher rate of muscle-preserving effort.
- Should I enter my body fat percentage?
- Only if you have a reasonably reliable reading, from calipers, a DEXA scan, or a bioelectrical impedance scale used consistently. With it, the calculator switches to the Katch-McArdle formula, which estimates RMR from lean body mass instead of total weight. This is more accurate for people who are noticeably leaner or more muscular than average, since Mifflin-St Jeor assumes a typical body composition for a given weight and height.