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Calorie Deficit Calculator Guide
A calorie deficit means eating less than you burn. This works out the daily target for a given rate of loss, and how long a goal would take.
Daily target = TDEE − (weekly loss × 3,500 ÷ 7)
One pound of fat is roughly 3,500 calories; one kilogram is roughly 7,700.
TDEE 2,500 and a 1 lb/week goal means a 500/day deficit — a 2,000 calorie target.
The Floor Is Not Optional
This calculator won't recommend below 1,200 calories a day for women or 1,500 for men, and if your target would fall under that it says so instead of showing the number.
That isn't caution for its own sake. Below those levels it becomes very hard to get adequate protein, vitamins and minerals from food, and the deficit starts eating muscle alongside fat. If the arithmetic demands a target that low, the answer is a slower rate — not a smaller plate.
The 3,500 Rule Is an Approximation
It's a useful starting point and it's wrong in an interesting way.
The rule assumes your TDEE stays put as you lose weight. It doesn't. A smaller body burns fewer calories, so the deficit you started with shrinks as you succeed — which is why linear predictions overshoot on long timelines. Expect a real curve that flattens, and recalculate every 10–15 lb.
Why the Scale Lies for Weeks at a Time
Fat loss is slow and quiet. Water weight is fast and loud, and it's the only thing you see day to day.
Glycogen holds roughly three grams of water per gram. Change your carbs, your salt, your training or where you are in your cycle and the scale swings several pounds in a day — with no fat involved. This is why people abandon working plans in week two. Weigh weekly, compare trends over a month, and ignore individual readings.
Faster Isn't Better
Aggressive deficits cost muscle, energy and adherence. The plan you follow for six months beats the plan you quit in three weeks, and 0.5–1% of body weight per week is the range most people can actually sustain while holding on to muscle. Protein and resistance training are what protect muscle in a deficit — the deficit itself doesn't care where the weight comes from.
When Not to Use This
Don't use a deficit calculator if you're pregnant or breastfeeding, if you're under 18, or if you have any history of disordered eating. If your relationship with food or numbers is difficult, a calculator is not the tool — a doctor or dietitian is.
Related: TDEE calculator, macro calculator, protein intake calculator.
This is an estimate for general information, not medical advice. Your needs depend on factors no calculator can see. Speak to a doctor or a registered dietitian before making significant changes, especially if you have a health condition or a history of disordered eating.
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