Sprint 7 Health Hub
Calorie Deficit/Surplus Calculator
Compare target calories vs maintenance.
Deficit / Surplus
105 kcal
How it works
A calorie deficit means consuming fewer calories than you burn — the only mechanism by which fat loss occurs. A calorie surplus means consuming more than you burn — required for muscle gain. The Calorie Deficit/Surplus Calculator determines your Total Daily Energy Expenditure (TDEE), then calculates the daily calorie target for your specific goal (fat loss, muscle gain, or maintenance) and projects the expected outcome over time.
How TDEE is calculated: TDEE = Basal Metabolic Rate (BMR) × Activity Multiplier
BMR is calculated using the Mifflin-St Jeor equation (most accurate for most people): - Men: (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5 - Women: (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
Activity multipliers: - Sedentary (desk job, no exercise): × 1.2 - Lightly active (1–3 days exercise/week): × 1.375 - Moderately active (3–5 days/week): × 1.55 - Very active (6–7 days hard exercise): × 1.725 - Extremely active (physical job + hard training): × 1.9
Deficit/surplus guidelines: - Moderate fat loss: TDEE − 500 kcal/day → approximately 0.5kg (1 lb) fat loss per week - Aggressive fat loss: TDEE − 750 kcal/day → approximately 0.75kg fat loss per week (upper limit before muscle loss risk increases) - Lean bulk: TDEE + 200–300 kcal/day → minimal fat gain while building muscle - Standard bulk: TDEE + 500 kcal/day → faster muscle gain with some fat gain
One pound of fat equals approximately 3,500 kcal. Projections are estimates — individual metabolism varies by 10–15% from formula predictions.
Privacy: all calculations run in the browser. No health data is transmitted.
Frequently Asked Questions
- A deficit of 500 kcal/day (producing approximately 0.5kg or 1 lb of fat loss per week) is the standard moderate recommendation. A deficit of 750 kcal/day is the upper practical limit for most people before muscle loss, hormonal disruption, and metabolic adaptation become significant concerns. Very large deficits (1,000+ kcal/day) cause more lean mass loss, reduce NEAT (non-exercise activity thermogenesis), increase cortisol, and produce rebound eating — the rate of loss slows as the body adapts, and compliance collapses.
- Basal Metabolic Rate (BMR) is the calories burned at complete rest — literally if you lay still all day. Total Daily Energy Expenditure (TDEE) adds the calories burned through all daily activity (exercise, walking, fidgeting, digestion). Eating at BMR while living a normal life creates an accidental large deficit — the correct maintenance level is TDEE, not BMR. The Mifflin-St Jeor BMR formula multiplied by an activity factor produces TDEE — the correct baseline for fat loss or gain calculations.
- Multiple mechanisms cause plateau and slowdown: (1) metabolic adaptation — the body reduces TDEE by 5–15% in response to sustained deficits; (2) NEAT reduction — unconscious movement (fidgeting, spontaneous walking) decreases; (3) you now weigh less, so the same activities burn fewer calories; (4) glycogen and water depletion in early weeks inflates initial loss rate — fat loss continues but appears slower. Strategies: periodically recalculate TDEE at current weight, incorporate re-feeds (maintenance calories for 1–2 days weekly), and increase NEAT through more daily steps.
- For lean muscle gain with minimal fat, a surplus of 200–300 kcal/day above TDEE is optimal for most people. This is the 'lean bulk' approach — muscle can only be synthesised at a rate of roughly 0.5–1kg per month for natural lifters, so a large surplus simply adds fat without accelerating muscle gain beyond physiological limits. Beginners can gain muscle and lose fat simultaneously ('body recomposition') in a small deficit with adequate protein — a surplus is more important for intermediate and advanced lifters.