Calorie Deficit Calculator

How the calculator works

A “calorie deficit” simply means eating fewer calories than your body burns. To find that number, the calculator runs three steps:

1. Resting metabolic rate (BMR/RMR) via the Mifflin-St Jeor equation [1], the most accurate widely-used predictive equation for healthy adults:
   Male: 10 × kg + 6.25 × cm − 5 × age + 5
Female: 10 × kg + 6.25 × cm − 5 × age − 161
2. Maintenance calories (TDEE) by multiplying BMR by an activity factor [4]: Sedentary ×1.2, Lightly active ×1.375, Moderately active ×1.55, Very active ×1.725, Extra active ×1.9.
3. Deficit using the classic approximation that ~3,500 kcal equals about one pound of body fat. A daily deficit of rate × 3,500 ÷ 7 targets that rate of loss — e.g. 1 lb/week ≈ a 500 kcal/day deficit, 2 lb/week ≈ 1,000 kcal/day. Your target intake is simply TDEE − daily deficit.

The safety floor

A bigger deficit is not always better. The calculator never recommends eating below roughly 1,200 kcal/day for women or 1,500 kcal/day for men [3]. If your chosen rate would push you under that floor, the tool caps your target at the floor and tells you the slower-but-safer loss rate you can actually expect. Eating below the floor without medical supervision risks nutrient deficiencies, muscle loss, and metabolic adaptation that stalls progress.

Why the estimate isn't a guarantee

The 3,500-kcal-per-pound rule is a useful planning shortcut, but real-world energy balance is dynamic [2]: as you lose weight your body burns fewer calories, so loss tends to slow over time even if you hold the same intake. Water weight, sodium, sleep, stress, medications, and menstrual cycles all move the scale day to day. Treat the numbers here as a starting point and adjust based on 2–4 weeks of real data.

Where GLP-1 medications fit in

The number-crunching is straightforward; the willpower is not. The single hardest part of any deficit is sustaining it against rising hunger. That is exactly the problem GLP-1 medications like semaglutide and tirzepatide solve — they reduce appetite and slow gastric emptying, making the same calorie target far easier to hold. If you want to see how much weight the clinical trials predict at your starting weight, use our GLP-1 weight loss calculator, and if cost is the deciding factor, compare the cheapest semaglutide options.

Important disclaimer

This tool is for educational purposes only and does not constitute medical advice, diagnosis, or treatment. Calorie estimates are population averages and may not reflect your individual metabolism. Consult your healthcare provider or a registered dietitian before starting any weight-loss plan — especially if you are pregnant, breastfeeding, under 18, an older adult, or managing a chronic condition.

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