How many calories to lose 1kg (or a pound) a week?

To lose 1kg of body fat you need a calorie deficit of roughly 7,700 kcal. Spread over a week that is about 1,100 kcal a day less than you burn, which is a big cut. A gentler and more realistic target is 0.5kg a week, which needs a deficit of around 3,850 kcal over the week, or about 550 kcal a day. In old money, losing 1lb a week needs a deficit of roughly 3,500 kcal, near enough 500 kcal a day.

Here is where the numbers come from and how to use them without going hungry.

Where the 7,700 comes from

A kilogram of body fat stores roughly 7,700 kcal of energy. That figure is a long-standing rule of thumb used across nutrition, and it is close enough for planning even if nobody's body follows it to the decimal.

The logic is simple. To lose that kilogram, your body has to burn 7,700 kcal more than you eat. It does not matter whether the gap comes from eating less, moving more, or a bit of both. Create the deficit and the fat gets used for fuel.

The weekly maths

Break 7,700 down over seven days and you can see what each pace asks of you.

Working in pounds instead:

• 1lb a week needs about 3,500 kcal over the week, so roughly 500 kcal a day.
• 2lb a week needs about 7,000 kcal, so roughly 1,000 kcal a day.

So the popular "500 kcal a day" advice lines up with losing about 1lb, or a bit under half a kilo, each week. That is the pace most people can hold without their willpower giving out.

Why 1kg a week is harder than it sounds

A 1,100 kcal daily deficit is a lot. To manage it you either eat very little, burn a huge amount through exercise, or both. For many people that either drops them below a sensible eating floor or leaves them starving by mid-afternoon.

There is another catch. The 7,700 figure assumes you are losing pure fat. In practice a very aggressive deficit tends to cost you some muscle and water too, which is not what you want. Slower loss protects muscle better and is far easier to keep going.

This is why 0.5kg a week is the pace most guidance settles on. It is quick enough to see real progress on the scale within a few weeks, and gentle enough that you are not white-knuckling it.

The sensible floor

Whatever the maths says, there is a lower limit on how little you should eat. As a rough guide, most women should not drop below about 1,200 kcal a day and most men not below about 1,500, unless a doctor or dietitian is guiding them.

Here is the trap. If your daily burn is, say, 1,800 kcal, then a full 1,100 kcal deficit would put you at 700 kcal a day. That is well under the floor and a bad idea. When the deficit you would need pushes you below the floor, the answer is not to eat dangerously little. It is to accept a slower pace, or to add movement so you are burning more rather than eating far less.

Steady wins. Half a kilo a week is 26kg over a year if you hold it, and almost nobody needs to lose that much.

Let the maths run itself

Fettle (stayfettle.com) sets your daily target from the pace you pick, so you can choose 0.5kg a week and it works out the deficit and keeps you above a sensible floor. You log your food against it, with UK foods and barcode scanning to make it quick. It is free and needs no account.

A quick honest note

The 7,700 kcal figure is a planning average, not a precise law of your body. Real loss depends on water, muscle, hormones and how accurate your logging is, so expect the scale to wobble week to week. Judge progress over a month, not a day.

This is general information, not medical advice. If you have a health condition, are pregnant, or want a weight plan built around your own needs, speak to your GP or a registered dietitian first.