Calorie Deficit Calculator

The only rule of fat loss

Strip away the diets, the supplements, and the internet arguments, and fat loss comes down to one thing: a calorie deficit. Eat less energy than you burn and your body makes up the difference from stored fat. Keto, fasting, low-fat, carnivore — every approach that has ever worked did so by creating a deficit, whether it admitted it or not.

This calculator turns that principle into a concrete plan: your daily calorie target, how big the deficit is, how fast you will lose, and roughly when you will hit your goal weight — with a built-in safety check so you never diet harder than is wise.

How a deficit is calculated

We start with your TDEE — the calories you burn in a day. Subtract your chosen deficit and you have your daily target. To translate calories into pounds and kilograms, we use the well-known rule of thumb: about 7,700 calories per kilogram of body fat (≈3,500 per pound). So a 550-calorie daily deficit works out to roughly half a kilo (just over a pound) per week.

This is an estimate, not a law of physics for your exact body — water, glycogen, and metabolic adaptation all add noise week to week. That is why you plan with the calculator and then adjust based on the scale.

How aggressive should you go?

The right deficit balances speed against sustainability and muscle retention. A useful frame is percentage of bodyweight per week:

• 0.5% / week: gentle — great for the last few kilos or protecting performance.
• 0.5–1% / week: the sweet spot for most people, most of the time.
• Over 1% / week: fast, appropriate only when you have more to lose, and best time-limited.

The heavier you are, the faster you can safely lose; the leaner you get, the slower you should go to keep muscle. Our calculator flags any target that drops below the safe calorie floor.

Losing fat without losing muscle

A deficit tells your body to shed tissue — your job is to make sure that tissue is fat, not muscle. Two levers do almost all the work:

1. Eat enough protein. This is non-negotiable in a deficit. Set your target with the Protein Calculator (roughly 1.8–2.4 g/kg).
2. Keep lifting. Strength training signals your body to hold onto muscle. Even two or three short sessions a week make a decisive difference.

Get those right and the weight you lose comes overwhelmingly from fat — which is the whole point. Round it out with a full macro split from the Macro Calculator.

Breaking through plateaus

Almost everyone stalls eventually. It is rarely a broken metabolism — it is arithmetic. As you lose weight, you burn fewer calories, so the deficit that worked at the start becomes your new maintenance. When the scale sticks for 2–3 weeks despite consistency:

• Recalculate your target here with your new, lower weight.
• Tighten your food logging for a week — hidden calories creep in.
• Add daily steps rather than slashing calories further.
• Consider a short maintenance break (a diet break) to recover and reset.

Common mistakes

Going too hard, too soon

Crash deficits torch muscle and willpower. Slower is faster in the end.

Never recalculating

Your target must shrink as you do. Re-run this after every 4–5 kg (10 lb).

Under-eating protein

The fastest way to lose muscle instead of fat.

Weekend undoing

Two big weekend days can erase a weekday deficit. Judge intake across the whole week.

What to expect

Stick to a sensible deficit and you will see a quick initial drop (mostly water), then a steady grind of roughly 0.5–1% of bodyweight per week. Progress is not linear — expect whooshes and stalls — but the trend over a month tells the truth. Pair this plan with the simple, time-efficient training in our free 3-day program and you have everything you need to get lean and stay that way.