Once you know your TDEE, fat loss is a sizing decision: how big should the gap between burning and eating be? Too small and progress hides inside measurement noise; too big and hunger, fatigue, and muscle loss collect the bill. The good news is that the sensible range is well mapped. This guide lays out the numbers, and our free calorie calculator turns any deficit into a daily intake target.
In this guide
The exchange rate: calories to fat
Body fat stores roughly 7,700 kcal per kilogram (the familiar 3,500 per pound). That single number converts any deficit into an expected pace:
- 500 kcal/day × 7 = 3,500 kcal/week ≈ 0.45 kg (1 lb) per week
- For half a kilo a week, the gap needs to average about 550 kcal/day
The exchange rate is approximate, real loss includes some water and, if you under-eat protein or skip training, some muscle, but it is accurate enough to plan with and to sanity-check results against. Where TDEE itself comes from is covered in the BMR and calories pillar, and how to measure yours from real data in the TDEE guide.
The three deficit sizes
Using our running example of a 2,759 kcal TDEE:
| Size | Deficit | Intake | Pace | Trade-off |
|---|---|---|---|---|
| Small | 250 to 300 | about 2,475 | about 0.25 kg/week | Easy to live with, slow, progress can hide in noise |
| Moderate | about 500 | about 2,259 | about 0.45 kg/week | The classic default: visible progress, manageable hunger |
| Aggressive | 700 or more | about 2,050 or less | 0.6 kg/week or more | Fast, but hunger, fatigue, and muscle risk rise sharply |
None of these is morally superior. A small deficit that survives twelve months removes more fat than an aggressive one abandoned in week five. The deficit you can keep is the right size, and most people discover that boundary by starting moderate.
Sizing by percentage, not a magic 500
The flat 500 kcal advice ignores body size. A 15 to 25% cut from TDEE scales properly:
- TDEE 2,759 → 15 to 25% = 414 to 690 kcal, so the flat 500 happens to sit nicely in range.
- TDEE 1,900 (a smaller person) → 285 to 475 kcal. A flat 500 here is already past the aggressive line.
A matching rule on the output side: aim to lose about 0.5 to 1% of body weight per week. For an 80 kg person that is 0.4 to 0.8 kg/week; the leaner you get, the closer to the bottom of that band you should run, because lean bodies surrender muscle more readily.
The floors you should not cross
- Do not eat below BMR as a routine plan. It is not a magic boundary, but intakes under the resting requirement are very hard to fuel training and protein needs from, and they usually mark a plan chosen by impatience.
- Protect protein. In a deficit, commonly cited targets run around 1.6 to 2.2 g per kg of body weight (128 to 176 g for an 80 kg person), precisely so the weight that leaves is fat rather than muscle.
- Keep training. Resistance work is the signal that tells a dieting body the muscle is still needed.
- Diet breaks are allowed. A week or two at maintenance every couple of months costs little arithmetic and buys sanity, NEAT recovery, and adherence.
When progress stalls
Order of suspects, most likely first: The NIH Body Weight Planner is the research-grade companion for setting targets, built on the same energy-balance science.
- Intake drift. Portions grow, tracking loosens, weekends expand. Re-tighten measurement before changing targets.
- Water masking. New training, more salt, or stress can hold a kilogram of water for weeks while fat keeps leaving. Judge three-week trends.
- TDEE moved. You are lighter, and lighter costs less; NEAT also dips during diets. Recompute, or better, re-run the two-week audit from the TDEE guide.
- The deficit was smaller than planned. The 7,700 exchange rate lets you compute your real deficit from the actual loss rate; the answer is often half the planned figure, which is information, not failure.
Frequently asked questions
Is a bigger deficit always faster in practice?
On paper yes, in practice only up to the point where adherence breaks. Aggressive deficits also trim NEAT and training output, which quietly shrinks the real gap. The paper advantage and the lived result diverge more the harder you push.
Should the deficit come from food or exercise?
Energy-wise they are interchangeable; practically, food is easier to control precisely, and activity is easier to sustain emotionally. Most durable plans cut most of the gap at the table and add movement for health and a margin of error.
Do I need to change the number on rest days?
If your TDEE multiplier already averages your week, no. Calorie cycling (more on training days, less on rest days) is an adherence tool, not extra physics; the weekly total is what decides the result.
How fast will the scale move in week one?
Usually faster than the math predicts, because lower food volume and carb stores shed water. Expect the honest, fat-driven pace to show from week two or three onward, which is exactly when judging should start.
Is this medical advice?
No. These are general planning numbers. Anyone with medical conditions, a history of disordered eating, lots of weight to lose, or simply doubt should size their plan with a qualified professional.