If you want to lose fat, it all starts in the same place: eating less energy than you burn. That is the calorie deficit. There is no magic food, no fat-burning tea, no trick that skips this law. But "eat less" without numbers is a recipe for going hungry, losing muscle, and quitting in three weeks. This guide teaches you to calculate your deficit with data, to set how much to cut, and to do it without your body rebelling.
What a calorie deficit is
Quick answer: A calorie deficit happens when you eat fewer calories than your body burns each day. Your body covers that gap by pulling from its reserves, mainly fat. It is the only condition that triggers weight loss: without a deficit, there is no fat loss, no matter which diet you follow.
Your total daily energy expenditure (TDEE) adds up four things: your basal metabolism (what you burn at rest), the thermic effect of food, the exercise you do on purpose, and the involuntary movement of daily life. When you eat below that figure, you create the deficit.
The question is not whether the deficit works, but how much deficit suits you. Too small and you stall; too large and you lose muscle, energy, and your sanity. The sweet spot sits in a specific range that we are going to calculate.
How to calculate your calorie deficit step by step
Quick answer: Calculate your TDEE with the Mifflin-St Jeor formula multiplied by your activity factor. Subtract 15% to 25%, or roughly 300-500 kcal for moderate loss. Set protein first (1.6-2.2 g/kg), split the rest between fat and carbs, and readjust every 2-3 weeks based on your real progress.
Step 1: calculate your TDEE
Your basal expenditure comes from the Mifflin-St Jeor equation, the most reliable one for the general population. Then you multiply it by an activity factor (from 1.2 for sedentary to 1.9 for very active). Doing this by hand is tedious and error-prone, so use our macro calculator: enter age, weight, height, and activity, and it returns your TDEE in seconds.
Step 2: subtract your deficit
From that TDEE, cut 15% to 25%. If your expenditure is 2,400 kcal, a 20% deficit is 1,920 kcal a day. For most people, subtracting 300-500 kcal from maintenance gives sustainable loss without extreme hunger.
Step 3: set protein
Before touching fat or carbs, lock in protein: between 1.6 and 2.2 g per kilogram of body weight. This protects your muscle mass while you lose fat, according to the meta-analysis in British Journal of Sports Medicine, 2018.
Step 4: split fat and carbs
Put fat at 0.8-1 g/kg (needed for hormones) and fill the remaining calories with carbohydrates, your fuel for training. If you want to understand this split in depth, read our complete guide to calculating your macros.
Step 5: adjust every 2-3 weeks
No formula is perfect. The scale, the mirror, and your measurements rule over any calculation. If you lose nothing in 2-3 weeks, cut a bit more; if you drop too fast, eat more. The starting number is a starting point, not a verdict.
How much deficit is optimal
Quick answer: The optimal range is 15% to 25% below your TDEE, which usually means losing 0.5% to 1% of your body weight per week. Deficits more aggressive than 25% speed up muscle loss and sink your performance, so reserve them for short phases with protein kept high.
Notice that the pace is measured as a percentage of weight, not in fixed kilos. A 100 kg person can lose 1 kg per week with no problem; for a 60 kg person, attempting the same would be too aggressive. That is why "half a kilo a week for everyone" is bad advice.
There is the classic rule that 1 kg of fat equals about 7,700 kcal. It works as a mental reference, but it is approximate: your body is not a closed calculator. As you lose weight, your expenditure drops (we will cover this under metabolic adaptation), so the deficit that worked in month one may fall short by month three.
| Deficit | Typical pace | Who it's for |
|---|---|---|
| 10-15% | ~0.5%/week | Close to your goal, prioritizing muscle |
| 15-25% | 0.5-1%/week | Most people: moderate, sustainable loss |
| >25% | >1%/week | Short term only, high protein and supervision |
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Protein to keep muscle in a deficit
Quick answer: To preserve muscle mass while losing fat, eat between 1.6 and 2.2 g of protein per kilogram of body weight per day. It is the most decisive factor after the deficit itself: without enough protein, part of what you lose will be muscle, not just fat, and you will end up flabbier instead of leaner.
When you eat in a deficit, your body looks for energy wherever it can, and muscle is vulnerable. High protein, combined with strength training, tells your body that muscle is needed and must be kept. The meta-analysis by Morton and colleagues in British Journal of Sports Medicine, 2018, placed the useful ceiling for building and retaining muscle at around 1.6 g/kg, with room to go higher during cutting phases.
The recommendations by Helms and colleagues in Journal of the International Society of Sports Nutrition, 2014, go further for athletes in an aggressive deficit: up to 2.3-3.1 g/kg of fat-free mass. For most people who don't compete, the 1.6-2.2 g/kg of body weight range covers the goal with margin to spare.
If you want to dig into how much protein you need for your case, we have a science-based guide on daily protein. And if your specific goal is to show muscle while losing fat, check our macros for cutting.
Common mistakes when running a deficit
Quick answer: The most frequent mistakes are cutting too much at once, neglecting protein, failing to adjust when progress stalls, and ignoring metabolic adaptation. Almost all of them come from impatience: an aggressive deficit gives fast results at first, but usually ends in muscle loss, uncontrollable hunger, and quitting.
- Cutting too much. A 40% deficit drops weight fast, yes, but at the cost of muscle and performance. Fast is almost never sustainable.
- Forgetting protein. Without 1.6-2.2 g/kg, part of your loss will be muscle tissue. You will weigh less but with worse body composition.
- Not readjusting. Your deficit expires. What worked at the start falls short once you weigh less and your expenditure drops.
- Ignoring metabolic adaptation. Your body lowers its expenditure as you lose weight. The diet doesn't "stop working"; it's biology, managed with adjustments and rest.
This is where diet breaks and refeeds come in: raising calories to maintenance for a few days or a week to give a hormonal and psychological break. They don't halt long-term progress and often help sustain longer deficits. Metabolic adaptation is real, but it's not a sentence: it means you need patience and readjustment, not that you're broken.
How Makroa fits into your deficit
Quick answer: Makroa delivers refrigerated meals in Madrid built around the gram amounts your body needs, calculated for your deficit and your protein target. You run your numbers once, pick your meals, and receive real food that fits without weighing anything or cooking daily.
The theory of the deficit is simple; executing it every day is the hard part. Weighing rice, hitting protein at each meal, cooking on Sunday for the whole week: that is where most people fall off. Makroa covers that part. It's meal prep personalized by macros, so your meals already come planned for your deficit and your protein target.
Our culinary quality bar is high: healthy food you actually want to eat, not the sad diet chicken and broccoli. Refrigerated, never frozen. No subscription locking you in. Deliveries twice a week in Madrid, from 7.90€ a meal. To see how it works in your area, check our meal delivery in Madrid.
The ideal plan: calculate your deficit with the macro calculator, set your protein, and let the meals hit the numbers for you. You train, rest, and adjust every 2-3 weeks; the food is already handled.
Frequently asked questions
How many calories should I eat to lose fat?
Between 15% and 25% below your TDEE. If you burn 2,500 kcal, that's about 1,875-2,125 kcal a day. Calculate your exact TDEE with the macro calculator and subtract your deficit from there.
How much weight is healthy to lose per week?
Between 0.5% and 1% of your body weight per week. For someone at 80 kg, that's 400-800 g weekly. Going faster usually costs muscle.
Can I lose fat without counting calories?
You need a deficit, but you don't have to count every day yourself. Receiving meals already calculated to your macros is one way to hold the deficit without weighing or logging food.
Why did I stop losing weight?
Probably metabolic adaptation: as you weigh less, your body burns less. The fix is to readjust the deficit every 2-3 weeks or introduce a diet break, not to give up.