How to use Calorie Calculator
This calorie calculator estimates how many calories you should eat each day to lose weight, maintain your current weight or build muscle. It uses the Mifflin-St Jeor equation to calculate your Basal Metabolic Rate (BMR), multiplies by your activity level to find your Total Daily Energy Expenditure (TDEE), then adjusts by your goal: a 500 kcal deficit for weight loss, zero change for maintenance, or a 500 kcal surplus for muscle gain.
- Select your gender.
- Enter your age, height in centimetres and weight in kilograms.
- Choose your activity level from the dropdown.
- Pick your goal: Lose Weight, Maintain Weight or Gain Weight.
- Your daily calorie target updates instantly — no button press needed.
Your data never leaves your device — 100% private processing.
How calories are calculated
The Mifflin-St Jeor formula gives your resting calorie burn (BMR). Multiplying by an activity factor (1.2 to 1.9) gives TDEE. Adding or subtracting a goal adjustment gives your target: −500 kcal/day creates a deficit that results in approximately 0.5 kg of weight loss per week (since roughly 7,700 kcal = 1 kg of fat). The +500 kcal surplus supports muscle protein synthesis when combined with resistance training.
Why calorie counting is a starting point, not a perfect science
Food labels carry up to ±20% error, and individual calorie absorption varies with gut microbiome, food processing and meal composition. The 500 kcal deficit rule works on average, but individuals may need 400–700 kcal below TDEE depending on adaptive thermogenesis. Use this estimate as a starting target, weigh yourself weekly and adjust by 100–200 kcal every 2–3 weeks if weight is not moving in the expected direction.
Worked examples
Woman losing weight
Inputs: BMR 1,370 × 1.375 (light) = 1,884 TDEE, −500
Result: ≈ 1,384 kcal/day target
Man maintaining weight
Inputs: TDEE 2,720, maintenance
Result: ≈ 2,720 kcal/day
Man building muscle
Inputs: TDEE 2,720, +500 surplus
Result: ≈ 3,220 kcal/day
Goal adjustment and expected weekly change
| Goal | Daily adjustment | Expected weekly change |
|---|---|---|
| Weight loss | −500 kcal | ≈ −0.5 kg (−1 lb) |
| Maintenance | ±0 kcal | Stable weight |
| Lean bulk | +250 kcal | ≈ +0.25 kg |
| Muscle gain | +500 kcal | ≈ +0.5 kg |
Glossary
- BMR
- Basal Metabolic Rate — calories burned at rest for survival.
- TDEE
- Total Daily Energy Expenditure — total calories burned per day with activity.
- Calorie deficit
- Eating fewer calories than you burn, causing the body to use stored fat.
- Calorie surplus
- Eating more calories than you burn, enabling muscle growth when training.
Related reading
Frequently Asked Questions
Why use Calorie Calculator?
- Calculates a personalised daily calorie target for loss, maintenance or muscle gain in one step
- Applies a 500 kcal daily deficit linked to approximately 0.5 kg of weekly fat loss
- Combines Mifflin-St Jeor BMR with activity-level scaling for a more accurate TDEE base
- Instant results without a button press reduce friction for daily diet check-ins
Common use cases
- Determine a starting calorie target before beginning a 12-week cut or bulk phase
- Recalculate after significant weight change to refresh a daily target that has drifted out of range
- Compare calorie needs at two activity levels to quantify the impact of adding a workout day
- Use the maintenance figure as a diet reset baseline before starting a new goal phase
- Estimate the surplus needed to support muscle protein synthesis alongside resistance training
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