🔥 Calorie Deficit Calculator

What This Calculator Does

This calculator estimates how many calories your body burns per day (your TDEE — total daily energy expenditure) and shows what a mild, moderate, or larger calorie deficit looks like as a daily intake target, along with the weight change each pace implies. Enter your weight, height, age, sex, and activity level, and the numbers appear instantly.

A deficit only works if it is anchored to your actual maintenance number, and that number differs enormously between people. This tool replaces guessing with a recognized estimate, giving you a realistic starting point. It is general guidance for healthy adults — not medical advice, and not a substitute for professional support where that is appropriate.

How the Numbers Are Estimated

The starting point is your resting metabolism — the energy your body uses just existing — estimated with the Mifflin-St Jeor equation, one of the most widely used and validated formulas, built from your weight, height, age, and sex. That resting figure is then multiplied by an activity factor, from sedentary (about 1.2) through moderately active (about 1.55) to very active (about 1.725), producing your TDEE: the daily calories that keep your weight stable.

A deficit is simply an intake below TDEE. Because roughly 7,700 kcal corresponds to a kilogram of body fat (about 3,500 per pound), a 500 kcal daily deficit projects to roughly 0.45 kg (1 lb) per week, and a 250 kcal deficit to about half that. These projections are honest approximations: real bodies adapt, water weight fluctuates, and metabolism shifts as weight changes — so treat the weekly figure as a expected trend over weeks, not a guaranteed weekly reading on the scale.

Using a Deficit Sensibly

The evidence-backed advice is to favor the moderate path. A 250-500 kcal deficit is slow enough to sustain, preserves more muscle (especially combined with adequate protein and resistance exercise), and builds habits that survive after the deficit ends. Very aggressive deficits feel productive for a week and then collapse — hunger, fatigue, and rebound eating are the usual result, which is why the sustainable pace usually wins over months even though it looks slower on paper.

Some honest boundaries matter here. Estimates are averages: your true TDEE may sit meaningfully above or below the formula, so the practical method is to start at the calculated target, track for two to three weeks, and adjust based on the real trend. Do not push intake to extreme lows — most guidance treats very low calorie levels as territory for medical supervision only. And if you have any medical condition, take medications that affect weight, are pregnant, or have any history of disordered eating, the right first step is a healthcare professional rather than a calculator. Used within those limits, a TDEE-anchored deficit is the most reliable, level-headed way to approach gradual weight change.

Why Progress Stalls and What Actually Helps

Almost everyone in a deficit hits a stretch where the scale stops moving, and knowing why prevents the two classic mistakes (giving up, or slashing intake drastically). Part of it is physics: as weight drops, TDEE drops with it — a lighter body burns fewer calories — so the deficit that worked at the start quietly shrinks. Part is adaptation: the body economizes somewhat under sustained restriction. And a large part is water: glycogen changes, sodium, stress, and hormonal cycles swing daily scale weight by more than a week's true fat change, easily masking real progress for two or three weeks at a time. The trend over weeks is the signal; any single weigh-in is noise.

The evidence-aligned responses are modest and boring, which is why they work. Recalculate TDEE every 5–7 kg of change and adjust the target. Weigh daily but judge only the 7-day average, or weigh weekly under identical conditions. Audit tracking honesty before concluding metabolism is broken — untracked bites, oils, and weekend drift explain most “mystery” plateaus. Keep protein adequate and continue resistance training so the weight lost stays predominantly fat. And schedule maintenance breaks on long journeys: a week or two eating at TDEE is psychologically restorative and does not undo progress. A stall is information, not failure — usually it means the numbers need a small update, which is exactly what this calculator is for.

Quick Tips

• A 500 kcal/day deficit projects to roughly 0.45 kg (1 lb) per week.
• Moderate deficits sustain better than aggressive ones — the slower pace usually wins over months.
• Track your real trend for 2-3 weeks and adjust; formulas are starting estimates.
• Protein and resistance exercise help preserve muscle while in a deficit.

Frequently Asked Questions

What is a calorie deficit?

Eating fewer calories than your body burns. Your total daily energy expenditure (TDEE) is what you burn; consuming below it forces the body to draw on stored energy, which is how gradual weight loss works.

How is my TDEE estimated?

The calculator uses the Mifflin-St Jeor equation — a widely used formula based on weight, height, age, and sex — to estimate your resting metabolism, then multiplies by an activity factor for your lifestyle. It is a well-regarded estimate, though individual metabolisms vary.

How big should my deficit be?

A moderate deficit of about 500 kcal/day — roughly 0.45 kg (1 lb) per week — is the commonly recommended sustainable pace. Larger deficits lose faster but are harder to sustain and can cost muscle; most guidance advises against very aggressive cuts without professional supervision.

Is this medical advice?

No. It applies population formulas to your inputs for general guidance. Individual needs vary with health conditions, medications, and history — before starting a significant deficit, especially with any medical condition or a history of disordered eating, consult a healthcare professional.

General Guidance, Free to Use

This calculator runs entirely in your browser and gives estimates from population formulas — it is not medical advice. It works instantly, needs no account or download, and runs on any device. Like every tool here, it is free to use as often as you like.

Related Tools

For related health tools, the BMI calculator screens weight relative to height, the ideal weight calculator shows formula-based ranges, and the water intake calculator estimates hydration.