How Big Should Your Calorie Deficit Be?

How much to cut, how fast you can safely lose, and why the biggest deficit is almost never the best one.

The short answer

What a calorie deficit actually is

A calorie deficit means eating less energy than you burn. Your body makes up the difference from stored energy, most of which is fat. There is no mechanism by which fat loss happens without one, and no food that creates one by itself.

The number you are eating below is your total daily energy expenditure — everything you burn in a day, not just your workouts. Training is a smaller slice of it than most people expect: usually 10-20% of the total, while simply being alive accounts for 60-70%.

That explains a common frustration. Adding a fourth gym session a week moves your expenditure far less than eating 400 fewer calories a day does. Training is how you keep the muscle; the deficit is how you lose the fat.

How big should it be?

Size the deficit by the rate of loss you want, not by a round number that sounds decisive. The usual guidance is 0.5-1% of bodyweight per week, and it scales across body sizes in a way that "eat 1,500 calories" never does.

A kilogram of body fat holds roughly 7,700 kcal, so losing 500 g a week needs about 550 kcal a day below maintenance. That arithmetic is where the daily figures above come from.

Pick the lower end if you are already fairly lean, if you are training hard and want to keep your lifts, or if you have tried aggressive cuts before and not finished them. Pick the higher end if you have a lot to lose — in which case the early weeks are also flattered by water.

Why the biggest deficit is not the best one

A very large deficit does lose weight faster. It also costs more of that weight as muscle, and muscle is the thing you are training to keep. Past roughly 1% of bodyweight per week, the proportion coming from lean tissue climbs quickly.

• Your lifts stall, then fall. The most reliable early sign of an over-aggressive cut is the working weight on your main lifts dropping week after week.
• Hunger stops being background noise. A deficit you think about all day is one you will eventually stop keeping.
• Recovery gets worse. Less food means less fuel for training and less material to repair it with.
• It is harder to hold. Twelve weeks at 400 kcal below beats three weeks at 900 and nine weeks of giving up.

The floor worth respecting is your basal metabolic rate — the energy your body uses at rest. Eating below that for extended periods is where the trade stops being worth making.

What to eat while you are in one

A deficit decides whether you lose weight. What you eat inside it decides how much of that weight is fat.

• Protein matters most in a cut. 1.6-2.2 g per kilogram of bodyweight per day, higher within that range the leaner you get.
• Keep lifting. Training is the signal that tells your body the muscle is still needed; without it, a deficit takes what it likes.
• Fat and carbohydrate split the rest however suits your appetite and your training. There is no metabolic advantage to either, and a large adherence advantage to whichever you find easier.

How to tell whether it is working

Not from the scale on any single morning. Bodyweight moves by a kilogram or more day to day on water, salt and what is still in transit through you. Weighing daily is fine and useful; reading any one of those numbers as progress is not.

1. Weigh yourself at the same time each day, ideally after waking and before eating.
2. Compare this week average against last week average. That is the number that means something.
3. If the weekly average has not moved in two to three weeks, your deficit is smaller than you think.
4. If it is falling faster than about 1% a week and your lifts are going backwards, it is bigger than you want.

Your estimated expenditure is a starting guess, not a measurement. What you actually ate and what your weight actually did, over a fortnight, is a measurement — and it beats any formula.

When the loss stops

A genuine plateau — three weeks of flat weekly averages while you are still eating what you believe you are eating — has a small number of causes, and none of them is mysterious.

• Portions have crept. This is the most common cause by a wide margin, and it is not dishonesty: untracked oil, drinks and things eaten standing up add up to hundreds of calories.
• You are moving less. Deficits quietly reduce spontaneous movement — fewer steps, less fidgeting — and that is real expenditure disappearing.
• You are lighter now. Someone 6 kg down burns less than they did at the start, so the deficit that worked in week one is smaller by week ten.
• Weeks are not being counted honestly. Five tracked days and two untracked ones is often maintenance with extra steps.

The fix is almost never a bigger deficit. Tighten the tracking for a fortnight, recalculate against your current weight, and check whether the target was ever the problem.

Frequently asked questions