How to lose 10 kg: what it means in calories and time

By linear arithmetic, 10 kg is about 77,000 kcal: around five months at a deficit of 500 kcal a day, or around two and a half months at 1,000 kcal. In practice it takes longer, because energy expenditure falls along with body weight. In a model developed by NIH researchers, a 100 kg man who cuts his intake by about 480 kcal a day loses around 11 kg in the first year, not the 22 kg the linear calculation promises.

How many calories are in 10 kg

Calculations usually rely on the "3,500 kcal per pound" rule, or about 7,700 kcal per kilogram of lost mass. That gives 10 kg × 7,700 = 77,000 kcal: the amount of energy you need to take in below your expenditure.

The rule describes a kilogram of body tissue, not a kilogram on the scale. Why it cannot simply be multiplied by a number of days is explained in the article on calories in a kilogram of fat. Here it serves only as a starting point.

Timelines at different deficits

Divide 77,000 kcal by a daily deficit and you get the timeline by linear arithmetic.

This is arithmetic, not a plan, and it underestimates the time. The table assumes the deficit stays the same every day. In reality it shrinks on its own if your intake does not change. Your deficit depends on your calorie needs: how to estimate them is covered in the article on daily calorie needs, and how to choose the size of a deficit in the article on calorie deficits.

Why it takes longer in practice

The lower your weight, the less energy you use, both at rest and for any movement. An intake that created a 500 kcal deficit at the start creates a smaller one a few months later.

How much this changes the timeline is shown by the model of Kevin Hall and colleagues, published in The Lancet in 2011. It also powers the NIDDK Body Weight Planner. Two examples from the paper:

• A 100 kg man permanently eats 2 MJ (about 480 kcal) a day less than before. The linear rule promises a loss of 22 kg in the first year; the model predicts about half that.
• For a sedentary 100 kg man eating 3,000 kcal a day to lose 20 kg in 6 months, the model says he must cut his intake by 1,200 kcal a day.

For an average adult with excess weight, the authors derived a rule of thumb: a permanent change in intake of 100 kJ (about 24 kcal) a day eventually changes body weight by about 1 kg. About half of the change happens within a year and 95% within three years.

The same rule gives one more number. To keep your weight 10 kg below where it started, you need to eat, on average, about 240 kcal a day less than before you lost it. That is less than the deficit used to lose the weight, but it is not "eating as before" either. Maintenance is covered in the article on maintaining weight loss, and a drop in expenditure beyond the predicted one in the article on metabolic adaptation.

Why the first weeks go faster

At the start, the scale runs ahead of the calculation. Glycogen is stored together with water: according to Kreitzman and colleagues (1992), each part of glycogen is held with three to four parts of water. When the store is used up, the water goes with it.

In a study by Yang and Van Itallie (1976), six people with obesity spent 10-day periods on 800 kcal a day. On a mixed diet they lost about 278 g a day, 37% of it water. On a low-carbohydrate diet they lost about 467 g a day, 61% of it water.

So the rate of the first weeks should not be taken as the average. Later the pace slows to match the deficit, and some of the water returns after an ordinary dinner with a side of grains or potatoes. What changes in the first days is covered in "Can you lose weight in a week", and why weight jumps from day to day in the article on daily weight fluctuations.

10 kg or 5 kg in a month: what the arithmetic says

To take in 77,000 kcal less in 30 days, you need a deficit of about 2,570 kcal a day. For comparison, the sedentary 100 kg man in Hall's model uses about 3,000 kcal a day. He would have to eat about 430 kcal a day, and a person who uses about 2,000 kcal would not get there even by eating nothing at all.

Losing 5 kg in a month needs, by the same arithmetic, a deficit of about 1,280 kcal a day. The scale may show that number with a smaller deficit, but a noticeable part of it will be the water described in the previous section.

A day-by-day schedule does not make these numbers more achievable: the timeline is set by the size of the deficit, not by the order of meals. If you need a result by a specific date, start with the questions in "Losing weight for a date".

Why too large a deficit is risky

• Gallstones. NIDDK lists rapid weight loss, including on very low-calorie diets, as a risk factor for gallstones (its page on diet and gallstones).
• Muscle loss. In a trial by Vink and colleagues (2016), total weight loss was similar, 9.0 kg on 500 kcal a day and 8.2 kg on 1,250 kcal, but fat-free mass made up 8.8% of the weight lost in the first group and 1.3% in the second.
• Less than 1,200 kcal without supervision. The UK guideline NICE NG246 considers 800–1,200 kcal diets only within a specialist programme with long-term support, and diets under 800 kcal only when there is a clinically assessed need for rapid weight loss, such as before surgery. In both cases the diet lasts no more than 12 weeks, must be nutritionally complete, and comes with clinical supervision.

The rate at which weight loss stays safe depends on your starting weight and health. What studies show about fast and slow weight loss is collected in the article on weight loss rate.

How to organise tracking

Only records show whether a deficit is really there. In a systematic review by Burke and colleagues (2011) of 22 studies, regular recording of food, activity and weight was consistently associated with greater weight loss. The authors rated the evidence as weak: the samples were homogeneous and the data were self-reported.

1. Record your food every day, weekends included. Drinks, cooking oil and snacks go on separate lines. A photo food diary makes it easier to start.
2. Weigh your portions: a kitchen scale is more accurate than your eye. Without one, use the references in the article on estimating portion size.
3. Weigh yourself under the same conditions and compare one week's average with the previous week's, not one day with the next. How to read your own numbers is covered in "A week in the food diary".
4. Recalculate your calorie needs after every few kilograms: they fall along with your weight.

What a day of 1,200, 1,500 and 2,000 kcal looks like in grams of ordinary food is shown in a separate article: "1200, 1500, and 2000 kcal: how much food is that in grams". If your weight stays put despite a deficit in your diary, the reasons are covered in the article on weight loss plateaus.

When to see a doctor first

Your pace and calorie intake should be set by a doctor if any of these apply:

• diabetes, or thyroid, heart, kidney, liver or gallbladder disease;
• pregnancy or breastfeeding;
• taking medicines, especially those that affect blood glucose, blood pressure or weight (medicines and weight);
• being under 18;
• a current or past eating disorder: in that case, discuss calorie counting with a specialist beforehand; the signs are listed in the article on calorie counting and eating disorders.

If your body mass index is already in the healthy range, the question of losing ten kilograms is also best started with a doctor. And if you are losing weight without changing what you eat or how much you move, see a doctor in any case.

Count it from a photo

Frequently asked questions

How many calories do I need to cut to lose 10 kg?

By the 7,700 kcal per kilogram rule, about 77,000 kcal. That is a lower estimate: expenditure falls along with body weight, so an unchanged intake produces a smaller deficit over time.

How long does it take to lose 10 kg?

By linear arithmetic, about five months at a deficit of 500 kcal a day and about two and a half months at 1,000 kcal. In the model by Hall and colleagues, a 100 kg man who cuts his intake by about 480 kcal loses around 11 kg in the first year, so in practice the timeline is closer to a year.

Can you lose 10 kg in a month?

It would take a deficit of about 2,570 kcal a day. That is more than the entire daily expenditure of many adults: even eating nothing would not create such a deficit for them, and everyone else would have to eat only a few hundred kilocalories a day.

Can you lose 5 kg in a month?

The arithmetic requires a deficit of about 1,280 kcal a day. The scale may show 5 kg less with a smaller deficit, but much of the early loss is water stored with glycogen.

Why does weight come off quickly at first and then slowly?

In the first weeks you use up glycogen, and each part of it is stored with three to four parts of water. After that, the pace slows to match the deficit, and expenditure gradually falls along with body weight.

What calorie intake is too low?

The UK NICE guideline considers 800–1,200 kcal diets only in specialist programmes with support, and diets under 800 kcal only when there is a clinical need, for up to 12 weeks. These levels are not for use without a doctor.

Read next

• Weight loss rate: where the 0.5–1 kg per week guideline came from and what research says — The '0.
• Calorie deficit: how to calculate it and how to hold it — A calorie deficit is the one thing without which weight does not come down.
• How many calories are in a kilogram of fat and why the "7700" rule does not work — The rule is simple and therefore persistent: there are approximately 7700 kilocalories in a kilogram of fat, which means a deficit of 500 kcal per day results in half a kilogram per week and twenty-six kilograms per year.

Topics: What the research shows · Food diary

This article is for general information. It is not medical advice, a diagnosis, or a prescription for treatment or a diet, and it does not replace a consultation with your doctor. If you have a health condition, are pregnant, take medication, or follow a diet prescribed to you, decisions about food belong with your doctor.

Figures from regulations, guidelines and studies are given as they stood when this article was prepared and may since have changed; check them against the primary sources. This article is not advertising, an offer, or individual advice, and neither the author nor the site owner is responsible for decisions taken on the basis of it.