Fat loss
A deficit is not a diet, a food list or a rule about carbohydrates. It is one number being smaller than another — which is why it is simple to describe and surprisingly easy to get wrong in practice.
A calorie deficit means eating less energy than you burn. Size it at 10–20% below maintenance — usually 300–500 calories — and judge it on weekly averages, never on single weigh-ins. Anything steeper mostly buys you hunger and lost muscle.
The percentage framing matters more than the round number. A 500-calorie deficit is a gentle 17% for someone at 3,000 maintenance and a brutal 28% for someone at 1,800.
| Deficit | Weekly loss | Trade-off |
|---|---|---|
| 10% below maintenance | ~0.25% bodyweight | Easy to hold; slow; muscle well protected |
| 20% below maintenance | ~0.5–0.75% | The usual sweet spot |
| 25–30% below | ~1% | Hunger and fatigue rise sharply; short blocks only |
Deficits also have a shelf life. Twelve to sixteen weeks is about as long as most people hold one well. Taking two weeks at maintenance after a long block is not a failure of willpower — it restores appetite hormones, training quality and, quite often, the ability to start again.
Two things protect muscle in a deficit, and neither is optional if you care what the weight loss is made of:
Fibre and sleep are the two underrated ones. Thirty grams of fibre a day makes a deficit noticeably more comfortable, and a week of short sleep raises appetite enough to be measurable.
Almost every "my deficit stopped working" story turns out to be a logging story. The fix is to make logging fast enough that you keep doing it on the days you do not feel like it: scan the barcode for anything packaged, log in units rather than grams for the rest, and photograph the plate when neither applies.
Eating fewer calories than your body uses in a day, which forces it to draw on stored energy. Sustained over weeks, that stored energy is largely body fat.
Ten to twenty percent below maintenance, which for most people is 300 to 500 calories a day and produces roughly 0.25 to 0.75 kg of loss per week. Steeper deficits increase hunger and muscle loss without proportionally faster fat loss.
Twelve to sixteen weeks is a practical maximum for most people, followed by a week or two at maintenance. Longer uninterrupted deficits tend to degrade training quality, appetite control and adherence.
The most common causes are untracked weekends, under-logged cooking oils and sauces, portion drift, a maintenance figure that has fallen as you lost weight, and judging progress from single weigh-ins instead of weekly averages.
Diagnosing a stalled deficit needs weekly averages and honest logs, not a single weigh-in. NutriMacro keeps both, next to the training that the deficit has to support.
NutriMacro is a nutrition and training tracker for iPhone and Android. It logs food by barcode, photo or search, counts food in slices and units rather than grams, and keeps strength training, GPS activities, sleep and recovery in the same daily view. It runs in the language of your phone across 108 countries.
These are general guidelines for healthy adults, not medical advice. If you are pregnant, under 18, managing a health condition, or have a history of disordered eating, talk to a GP or a registered dietitian before changing how much you eat.
Read next: Calories to lose weight Calculating macros Portions without scales
