Calorie deficit: how many calories to lose weight?

A sensible calorie deficit is not a fixed number. Work from a rate: 0.5 to 1.0 percent of bodyweight per week. At 90 kg that is 450 to 900 grams. How many calories that takes depends on your own maintenance, not on the standard 500 kcal rule.

That standard rule is the problem. It holds for a few weeks, then it drifts, and almost nobody tells you why.

This is the arithmetic behind the complete plan for healthy weight loss. It covers the deficit only: how you set it, where the limits are, and when you recalculate.

Why the 3500 kcal rule is wrong

The rule of thumb says 3500 kcal equals a pound of fat. So 500 kcal a day less gives a pound a week, forever. That sum assumes your maintenance never changes. It does change. The lighter you get, the less you burn.

Every kilo you lose lowers your energy expenditure by roughly 20 to 30 kcal a day (PMID 29156185). Lose ten kilos and your maintenance sits 200 to 300 kcal below where it started.

Your appetite moves the other way at the same time. Per kilo lost, hunger rises by around 100 kcal a day. The appetite effect is three to five times the size of the metabolic one.

Put those side by side and you can see what happens to a fixed number. The deficit shrinks on its own. After a few months you are eating at maintenance while eating exactly what you ate in week one.

That is not a broken metabolism, that is arithmetic.

Why it still feels like a wall is covered in why your plateau is not a slow metabolism.

A deficit is a share, not a number

500 kcal means something different to everyone. For a 100 kg man with a maintenance of 2800 kcal, it is a deficit of 18 percent. For a small, sedentary woman with a maintenance of 1600 kcal, the same number is nearly 40 percent. Same subtraction, completely different intervention.

Eighteen percent is mild. You keep energy for your work and your training. Your muscle mass is barely at risk.

Forty percent is not mild. There you lose more muscle tissue than you need to, and the odds of sticking with it fall sharply.

That is why a share beats a number. It scales with your body, with your activity, and with every kilo that comes off.

Start from a rate, not from a subtraction

Start with the rate you want to hold: 0.5 to 1.0 percent of bodyweight per week. Norwegian researchers compared both ends in trained athletes. At around 0.7 percent per week the group gained fat-free mass. At around 1.4 percent per week it did not (PMID 21558571).

Translate that rate into kilos per week first. Only then into calories. The order is what keeps the number honest as you shrink.

A kilo of fat tissue costs roughly 7000 kcal. If you want 0.45 kg a week, that means a deficit of roughly 450 kcal a day. That number is true now, at this weight.

Not in three months.

The floors are not negotiable

There are two hard limits. Do not go below about 1200 kcal a day, because a complete diet becomes very hard to build under that. And a deficit larger than roughly a quarter of your maintenance belongs in a supervised programme, not in a sum you do yourself.

Below 1200 kcal it gets difficult to get enough protein, iron, calcium and fibre. The Dutch Voedingscentrum advises very low calorie diets only under the supervision of a doctor or dietitian. That advice exists for a reason.

Faster is not better either. In a steep deficit you lose a larger share of your weight as muscle tissue, and that tissue is what keeps your expenditure up.

Enough protein blunts that loss. In a meta-analysis, the higher protein group held on to 0.43 kg more fat-free mass and lost 0.87 kg more fat (PMID 23097268). Strength training does the rest.

Recalculate every four to six weeks

Your target drifts downward as you lose. So redo the sum every four to six weeks, using your current weight. Someone ten kilos lighter has a maintenance that sits hundreds of calories lower. The old number is simply out of date.

This is the step almost every calculation method skips. You get one number, and nobody mentions it has an expiry date.

Weigh yourself at fixed moments and look at the seven day average. Single days tell you nothing. Fluid and gut contents swing a lot, and that swing is bigger than your weekly loss.

Tracking what you eat is the best evidenced behaviour in weight loss (PMID 21185970). It is also exactly what shows you the week your deficit has evaporated.

How solid is that first number?

Less solid than the decimals suggest. Every formula estimates your maintenance from averages. Around any individual there is real error, in both directions. So treat your first result as a hypothesis, not as a verdict.

The correction does not come from a better formula. It comes from your own weight trend.

Two to three weeks of data say more than any estimate. If your seven day average falls too slowly, your estimate was too high. If it falls faster than the ceiling, it was too low.

Adjust in steps of 100 to 150 kcal a day. Not in jumps of 500. Large corrections make you hungry without giving you information any faster.

Which eating style you pick matters less than sticking with it. In DIETFITS, low carb versus low fat differed by 0.7 kg at twelve months, and that difference was not significant (PMID 29466592). The best approach is the one you are still doing a year later.

Counting calories is not for everyone

For some people, counting is a plain tool. For others it is fuel on a fire. If you have an eating disorder, or have had one, do not count and speak to your GP. The Dutch site Thuisarts has neutral information on this.

If counting starts to steer your mood, your sleep or your social life, that is a signal. Stop counting and work with fixed meal patterns instead of figures.

The tool should serve you, not the other way around.

What a blood test does and does not do here

A blood test will not tell you how many calories to eat. That number is in no tube. What blood does show is what your weight is doing to your health: fasting glucose, HbA1c, insulin, lipids and liver values. And it shows how those shift while you lose weight.

That is the honest role. Not an explanation for the scale, but a measurement of the risk underneath it.

Those values often respond before the weight does. What exactly changes is covered in what weight loss does to your blood values.

If you want a baseline before you start, the complete metabolic panel measures those values in one go. Repeat after three to six months. Then you see the direction, not just a figure on the scale.

When this article is not for you

Weight loss is not a healthy goal for everyone. Do not follow this article if you have or have had an eating disorder, are pregnant or breastfeeding, are under 18, are underweight, use insulin, or have had bariatric surgery. Speak to your GP first.

If thoughts about food or your body start to take over, talk to your GP or contact an eating disorder helpline. That is not weakness. That is sense.

What to do this week

Weigh yourself seven mornings in a row and write down the average. Then pick a rate of 0.5 percent of that weight per week. Convert it into a daily deficit and track what you eat for two weeks.

After those two weeks, compare your new seven day average. If it has not moved, take off another 100 to 150 kcal a day. And put a note in your calendar to redo the sum in four to six weeks, with your new weight.