How many calories do I need per day?
Your calorie needs depend on your Basal Metabolic Rate (BMR) — the energy your body burns at rest — multiplied by an activity factor that accounts for how much you move. This total is your TDEE.
BMR is calculated using the Mifflin–St Jeor equation — the most validated formula for the general population (±10% accuracy). When you provide body fat %, the calculator switches to Katch–McArdle, which is more accurate for athletes and lean individuals.
Male: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5
Female: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161
The three components of TDEE
Your TDEE is actually the sum of three distinct energy costs — not just BMR and exercise:
- BMR (60–70% of TDEE) — energy to keep you alive at rest: heart, brain, kidneys, liver, body temperature, cell repair. The largest single component.
- Physical activity — NEAT + exercise (20–30%) — every calorie burned through movement. This includes formal workouts and Non-Exercise Activity Thermogenesis (NEAT): fidgeting, walking to the kitchen, standing instead of sitting. NEAT varies by up to 400 kcal/day between similar-sized people — this is why two people eating identically can have very different results.
- Thermic Effect of Food — TEF (~10%) — energy your body spends digesting and processing meals. Protein has the highest TEF (~25–30% of its calories), carbohydrates around 7%, and fat only 2–3%. A high-protein diet quietly raises your TDEE.
The activity multiplier in this calculator captures both NEAT and exercise together. If you have a physically active job on top of gym sessions, choose a higher multiplier than you might expect.
Worked example — step by step
Here is exactly how the calculator arrives at a result, using a real set of inputs:
Example: Male, 32 years old, 80 kg, 178 cm, moderately active (×1.55)
BMR (Mifflin–St Jeor)1,847 kcal
TDEE (×1.55)2,863 kcal
Cut target (−500)2,363 kcal
Lean bulk (＋250)3,113 kcal
Protein (cut)154 g/day
Carbs (cut)242 g/day
Fat (cut)79 g/day
BMI25.2 (overweight)
Example: Female, 28 years old, 65 kg, 165 cm, lightly active (×1.375)
BMR (Mifflin–St Jeor)1,419 kcal
TDEE (×1.375)1,951 kcal
Cut target (−500)1,451 kcal
Lean bulk (＋250)2,201 kcal
Protein (cut)125 g/day
Carbs (cut)148 g/day
Fat (cut)48 g/day
BMI23.9 (normal)
How to use your TDEE to lose weight or build muscle
Fat loss
Eat 300–500 kcal below your TDEE. A 500 kcal daily deficit produces approximately 1 lb (0.45 kg) of fat loss per week. Never eat below your BMR for extended periods — this causes muscle loss, hormonal disruption, and metabolic slowdown.
Muscle gain
Eat 200–350 kcal above TDEE (lean bulk). Hit your protein target every day to maximise muscle protein synthesis — use the protein calculator for exact daily targets.
Maintenance
Eat at TDEE. If weight drifts unexpectedly after 2 weeks, adjust by ±150 kcal and reassess. Hit your protein target first, then fill remaining calories with carbs and fat to preference.
Why your TDEE might look wrong — common mistakes
The 5 most common TDEE errors
1Overestimating activity level. "Moderately active" means 3–5 hard gym sessions per week — not walking to the office. Most desk workers are Sedentary or Lightly Active. Choosing one level too high adds 200–400 kcal to your TDEE.
2Trusting smartwatch calories. Wearable devices overestimate calorie burn by 20–93% in research studies. Use your TDEE as the baseline — not your watch.
3Wrong body fat % estimate. Visual estimates of body fat % are often off by 5–10 percentage points. If unsure, leave the field blank and use Mifflin–St Jeor instead.
4Not recalculating after weight change. Losing 10 lbs lowers your BMR by ~80–100 kcal/day. What worked at 200 lbs will stall at 185 lbs if you don't update your targets.
5Confusing water weight with fat loss/gain. Carbohydrates store water (≈3g water per 1g glycogen). Cutting carbs can drop 3–5 lbs in a week — this is water, not fat. True fat loss is 0.5–1.5 lbs/week.
Frequently asked questions
What is the difference between BMR and TDEE?
BMR is calories burned at complete rest. TDEE is BMR × activity multiplier — your total daily burn including exercise. TDEE is typically 1.3–1.9× your BMR. Use TDEE, not BMR, as your calorie baseline.
How many calories should I eat to lose 1 pound per week?
A 500 kcal/day deficit below your TDEE produces approximately 1 lb of fat loss per week, since 1 lb of fat ≈ 3,500 kcal. For 0.5 lb/week, aim for a 250 kcal deficit. Deficits larger than 750 kcal/day risk muscle loss.
Why does adding body fat % change my result?
Standard formulas use total body weight. Muscle tissue burns ~3× more calories at rest than fat tissue. With body fat %, the Katch–McArdle formula isolates lean body mass, giving a more precise BMR estimate — especially for lean or muscular individuals.
Why do different TDEE calculators give different numbers?
Different calculators use different BMR equations (Mifflin–St Jeor, Harris–Benedict, Katch–McArdle) and may use slightly different activity multipliers. The Mifflin–St Jeor equation used here is the most validated for the general population. Results within 5–10% of each other are normal.
How often should I recalculate my TDEE?
Every 4–8 weeks, or after a 10 lb (4.5 kg) weight change. BMR decreases as you lose weight — not updating leads to stalled progress. A good habit: weigh yourself weekly and average over 4 weeks before adjusting calories.
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Results are estimates based on validated formulas. Not medical advice.