Calorie Deficit Calculator

TDEE · Macro Targets · Adaptive Projection · Week-by-Week Planner

Your Details

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Weight Loss Plan

Daily Target
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Deficit Scenario Comparison

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Chart: deficit scenario comparison.

Metabolic Adaptation Scenarios

Accounts for the body's tendency to reduce metabolic rate under prolonged deficit.

Bear (−15% adaptation)
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Slow metabolism / prolonged deficit
Base (−8% adaptation)
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Typical metabolic response
Bull (No adaptation)
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Linear loss — ideal scenario

Exercise Equivalents

Your daily deficit is equivalent to burning this much through exercise alone.

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Weeks to Goal — Sensitivity Matrix

How deficit size and goal amount interact. Your current selection is highlighted.

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Week-by-Week Weight Planner

Chart: week-by-week weight planner.
Week Date Expected Weight Adaptive Est. Total Lost Progress Milestone
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How to Use This Calculator

1

Enter Body Stats

Input your age, sex, height, weight, goal weight, and activity level. Choose the BMR formula that best fits your situation.

2

Set Your Deficit

Pick a deficit level (250–1,000 cal/day) or enter a custom daily calorie target. 500 cal/day = ~1 lb/week loss.

3

Review Your Plan

See your TDEE, macro targets, realistic timeline with metabolic adaptation, and week-by-week milestones.

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Formula & Methodology

Mifflin-St Jeor (Default)

Male: BMR = 10W + 6.25H − 5A + 5  |  Female: BMR = 10W + 6.25H − 5A − 161

W = weight(kg), H = height(cm), A = age. Most validated formula, ±10% accuracy for most adults.

Calorie Deficit & Weight Loss

Weekly Loss (kg) = (Deficit × 7) ÷ 7,700  |  3,500 kcal ≈ 1 lb fat

Adaptive thermogenesis: expect ~8% metabolic slowdown after 8 weeks, ~15% after 16 weeks of consistent deficit.

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Key Terms Explained

Calorie Deficit — Consuming fewer calories than your TDEE, forcing your body to use stored fat for energy.
TDEE — Total Daily Energy Expenditure — BMR × activity multiplier. Your true daily calorie burn.
BMR — Basal Metabolic Rate — calories burned at complete rest to sustain vital functions.
Adaptive Thermogenesis — The body's metabolic slowdown in response to prolonged calorie restriction, reducing effectiveness over time.
Katch-McArdle — BMR formula based on lean mass (not total body weight) — most accurate when body fat % is known.
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Real-World Examples

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Sarah

Sustainable Cut

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Creating a Sustainable Calorie Deficit

The 500-Calorie Rule

A 500 calorie daily deficit produces roughly 1 pound of fat loss per week under linear conditions. This moderate approach preserves muscle mass, keeps energy levels stable, and is sustainable long-term. Larger deficits often backfire through muscle catabolism, fatigue, and metabolic adaptation.

Accounting for Metabolic Adaptation

After 8–12 weeks of consistent deficit, the body reduces its resting metabolic rate by 5–15% — a phenomenon called adaptive thermogenesis. This means your week-17 results will differ from a purely linear projection. Periodic diet breaks at maintenance (1–2 weeks every 8–10 weeks) can partially reset this adaptation.

Protein: The Most Important Macro

During a cut, adequate protein (1g/lb of goal body weight or ~2.2g/kg) is critical for preserving lean muscle mass. Muscle tissue is metabolically expensive — losing it reduces your TDEE further, creating a negative cycle. Prioritize protein, then fat (≥20% of calories for hormonal health), then fill carbs with the remainder.

Diet vs. Exercise Deficit

Combining diet restriction and exercise is the most effective strategy. It is far easier to cut 300 calories from food and burn 200 through exercise than to achieve either alone. Exercise also signals muscle retention during a caloric deficit.

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Frequently Asked Questions

What is a safe calorie deficit for weight loss?+

A moderate deficit of 500-750 calories per day is generally considered safe and sustainable, resulting in about 1-1.5 lbs of weight loss per week. Deficits larger than 1,000 calories per day increase the risk of muscle loss, nutrient deficiencies, and metabolic adaptation.

Why does weight loss slow down after the first few weeks?+

Initial rapid weight loss is largely water and glycogen, not fat. As you lose weight, your body requires fewer calories (lower TDEE), which shrinks the effective deficit. Metabolic adaptation also causes your body to become more efficient. Periodic diet breaks or recalculating your deficit can help overcome plateaus.

Is the "3,500 calories per pound" rule accurate?+

The 3,500 calorie rule is a rough approximation that works reasonably well for short-term predictions but becomes less accurate over time. Real weight loss is non-linear because your metabolic rate decreases as you lose weight. This calculator accounts for that adaptation in its projections.

Should I create my deficit through diet, exercise, or both?+

A combination of both is most effective and sustainable. Reducing food intake by 300-500 calories and burning an additional 200-300 through exercise preserves more muscle mass, improves cardiovascular health, and is easier to maintain than extreme dietary restriction alone.

How do I know if my calorie deficit is too aggressive?+

Signs of an excessive deficit include persistent fatigue, hair loss, loss of menstrual period, constant hunger, poor workout recovery, and irritability. Women should generally not eat below 1,200 calories and men not below 1,500 calories per day without medical supervision.