A calorie calculator estimates how many calories you burn in a typical day (your Total Daily Energy Expenditure, or TDEE) and how many you'd need to eat to lose weight, maintain, or gain muscle. Enter your age, sex, weight, height, and activity level, the calculator returns four numbers: your resting metabolic rate (BMR), your maintenance calories, and adjusted targets for fat loss and muscle gain.
These numbers are starting points. Track your actual weight over 2-3 weeks and adjust by 100-200 calories if the scale isn't moving the way you expected, individual metabolic rates vary by ±10-15% from formula estimates.
What the calculator does not account for: medical conditions (thyroid disease, PCOS, diabetes), medications that affect metabolism, pregnancy or breastfeeding, recent extreme dieting (which suppresses metabolic rate by 10-20% in some studies), or non-exercise activity thermogenesis (NEAT) outside what's captured by the activity multiplier. The fat-loss target uses the standard 500 cal/day deficit (≈1 lb/week); the muscle-gain target uses a 300 cal/day surplus paired with adequate protein (0.8-1g per lb of bodyweight). For aggressive cuts or precise body recomposition, work with a registered dietitian, formulas establish the starting point, but real outcomes need real measurement.
Key takeaway
Your daily calorie target isn't really one number, it's a range that depends on activity level. The biggest mistake people make is using a static "2000 calorie" rule of thumb when their actual TDEE varies by several hundred calories per day depending on training volume. Maintenance is the calorie level where weight is stable; everything else (loss, gain) is just maintenance plus or minus a deliberate offset.
How it's calculated
This calculator uses the Mifflin-St Jeor equation, considered the most accurate of the widely-used metabolic-rate formulas for healthy adults:
- Men:
BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5 - Women:
BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
BMR is your resting metabolic rate, calories you'd burn just keeping the lights on if you stayed in bed. TDEE multiplies BMR by an activity factor (1.2 for sedentary up to 1.9 for very active) to estimate total daily burn including movement and exercise.
The weight-loss target subtracts 500 calories from TDEE, a moderate deficit that produces ~1 lb/week loss for most people. The muscle-gain target adds 300 calories, the typical surplus for lean muscle gain without excess fat.
Source: Mifflin-St Jeor equation
Examples
35-year-old man, 170 lb, 5'10", moderately active
- Age 35 years
- Sex Male
- Weight 170 lb
- Height 70 in
- Activity level Moderate (3–5 days/week)
BMR ≈ 1,712 calories, what a 35-year-old, 5'10", 170 lb man burns at rest. With moderate activity (3-5 training days/week), TDEE rises to about 2,654 calories. A 500-calorie deficit puts the weight-loss target near 2,154. For lean muscle gain at this body size, ~2,954 calories supports growth without excessive fat storage.
30-year-old woman, 140 lb, 5'5", lightly active
- Age 30 years
- Sex Female
- Weight 140 lb
- Height 65 in
- Activity level Light (1–3 days/week)
BMR ≈ 1,356 for a 30-year-old, 5'5", 140 lb woman with light activity (1-3 workouts/week). TDEE comes in around 1,864 calories. Note that the weight-loss target (~1,364 cal) lands within ~10 calories of her BMR, a sign the deficit is aggressive at this body size and might warrant a smaller cut (250-300 cal) instead.
Frequently asked questions
How accurate is this calculator?
The Mifflin-St Jeor formula (NIH/PubMed) is accurate within ±10% for about 80% of healthy adults. The remaining 20% have metabolic rates that deviate further due to genetics, body composition (very lean or very obese), thyroid function, or recent diet history (chronic dieters often have suppressed BMR). For these cases, formula estimates are a starting point; tracking real-world weight changes over 2-3 weeks gives a more accurate calibration.
Should I count calories accurately, or is a target enough?
For most people, the answer is somewhere in between. Tracking calories precisely for 2-4 weeks (using a food scale and a logging app) teaches you the calorie content of typical foods and meals. After that, most people can eyeball portion sizes and stay within ±10% of target without meticulous tracking. Athletes and bodybuilders who care about fine-tuned body composition tend to track more carefully; general weight-management goals work fine with directional awareness.
What's the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the energy your body uses at rest just to stay alive, heart beating, breathing, organ function. It's roughly 60-75% of total burn for a sedentary person. TDEE (Total Daily Energy Expenditure) is BMR plus everything else: physical activity, the thermic effect of food (~10% of TDEE), and non-exercise activity like fidgeting and walking. TDEE is the number you actually eat against; BMR is just the floor.
How fast can I lose weight safely?
Per CDC healthy weight-loss guidance, the conventional safe maximum is 1-2 lb per week for most people, which corresponds to a daily deficit of 500-1,000 calories. Faster loss is achievable but tends to come with more muscle loss, lower energy, worse recovery, and a higher chance of regaining the weight when the diet ends. Sustainable loss tends to be slower (0.5-1 lb/week) and prioritizes maintaining muscle mass through adequate protein (0.8-1g per lb of bodyweight) and resistance training.