Calorie Deficit Calculator Guide: How to Lose Weight Without Losing Muscle
Nutrition · 2026-02-14 · 7 min read
How to calculate your calorie deficit for weight loss — TDEE, deficit size, protein target, and the 4 mistakes that stall 80% of cuts.
There is only one number that matters in every weight-loss plan: how many calories you eat less than you burn each day. If you get that number right, your body composition changes in a predictable way. If you do it wrong, you might stall, lose muscle instead of fat, or bounce back three months later. This guide tells you exactly how to figure out your deficit and use it without hurting yourself.
The one-sentence summary
If you eat 300 to 500 fewer calories than you need to maintain your weight and get enough protein, you'll lose about 1 pound (0.45 kg) of fat per week in a healthy way.
That's the short version. The rest of this guide is about the four things that can make or break your success: "it worked" or "I gave up in week three."
Step 1: Figure out your TDEE (maintenance)
TDEE stands for Total Daily Energy Expenditure. It is the number of calories you burn in a day, including exercise. It's the point of reference. The quickest way to get a reliable answer is to use the Mifflin-St Jeor formula and an activity multiplier:
BMR (men) = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
BMR (women) = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
TDEE = BMR × activity multiplier:
- • Sedentary (no exercise, desk job): ×1.2
- • Light (1–3 workouts a week): ×1.375
- • Moderate (4–5 workouts a week): ×1.55
- • Active (6 or more workouts a week): ×1.725
Don't want to do maths? Our free TDEE calculator does it right away and shows you the ranges of the deficit next to each other.
Step 2: Choose the size of your deficit
A bigger deficit means losing weight faster, but it also means losing more muscle, feeling hungrier, and having more people drop out. This is what really works:
| Size of the deficit | Weekly weight loss | Best for | Trade-off |
|---|---|---|---|
| Small: 200–300 kcal | 0.3–0.5 lb | Want to keep muscle, even though I'm already lean | Takes time, needs patience |
| Moderate: 400–500 kcal | 0.8–1.0 lb | Most people, most of the time | Hunger that can be controlled |
| Aggressive: 600–800 kcal | 1.2–1.6 lb | A deadline for an event and more body fat (more than 25% for men and more than 32% for women) | More muscle loss makes it harder to stick to |
| Extreme: 1000+ kcal | 2+ lb | Not often right | Muscle loss, metabolic downregulation, and rebound risk |
Step 3: Get your protein goal right
This is the part of a cut that people skip the most. In a deficit, protein does three things that nothing else can do:
- Keeps your muscles from breaking down. If you don't get enough protein, your body will break down muscle.
- Controls hunger. High-protein meals are by far the best at making you feel full.
- Burns more calories to digest. It takes more energy to digest: 20 to 30% thermic effect compared to 5 to 10% for carbs and fat.
The goal is to get 0.8 to 1 gram of protein per pound of body weight each day (1.8 to 2.2 g/kg). That's 145 to 180 grams of protein every day for a person who weighs 180 pounds. Not up for negotiation during a cut.
Step 4: Keep an eye on your weight trend, not your daily weight
Water, sodium, glycogen, and bowel contents can cause your weight to change by 2 to 4 pounds every day. If you weigh yourself every day and get scared when the numbers go up, you'll stop. Instead:
- Every morning, weigh yourself under the same conditions (after using the toilet and before drinking water).
- Don't look at the daily number; look at the 7-day moving average.
- Add a weekly body fat photo so you can tell the difference between losing fat and water.
- If the 7-day average hasn't changed in two weeks, cut back on 100 to 150 kcal.
Common deficit mistakes
"I'll eat 1200 calories and lose 3 pounds a week."
You will lose three pounds, but two of them will be muscle and water. Your metabolism slows down, your hunger goes up, and you gain weight.
"I don't need to track; I know what I'm eating."
Studies show that people who report their own calorie intake are off by 20 to 40%. This is almost always the reason why you're not losing weight in a planned deficit.
"No carbs, all protein."
Works for a short time because glycogen loses water (the "big scale drop"). Cutting back on carbs over time makes it harder to train, which means lifting doesn't protect your muscles as well.
Put it all together
To lose weight, figure out your TDEE, then take away 400 to 500 calories. Hit 0.8g of protein per pound of body weight. Weigh yourself every day and look at the 7-day average. Take a weekly body fat photo to make sure you're losing fat and not muscle. If the trend stops for two weeks, make changes. That's all. All the other sounds are just noise.
Use our free TDEE, deficit, and protein calculators to get started. Then, every Sunday, check your trend against your target body fat range.
Keep reading
- Why most men over 40 never get lean — in 16 slides — The hidden calories you never sat down for, why the weekend cancels the week, and the skill of being slightly hungry without treating it as an emergency.
- DUP-3: Why I Train the Same Muscle at Three Different Rep Ranges Each Week — Rhea 2002: same exercises, same total volume, half the time — DUP gained 2x more strength than linear periodization. The 3-rotation version, in plain words.
- APRE 10: The Quiet Algorithm That Picks Your Working Weight For You — Mann's D-1 football protocol in 4 sets. Why the algorithm out-progresses linear programs by ~2x on bench and squat — and how to run it without thinking.
- Best Exercises for Biceps Peak (And the Honest Truth About Genetics) — Why biceps peak is 70% genetics and 30% training — and the exact 30% you can change with long-head-biased curls.
- The 60-Second Scan: How to Read a Restaurant Menu for Calories — Why "grilled chicken salad" can be 1,100 calories, and how 6 menu keywords tell you everything about calorie density in under a minute.
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