How many kilos you can safely lose in a month

When you start a diet, you want to see results quickly. The question is how fast you can go without paying for it with muscle, tiredness or health problems. The guidelines give a range, and the studies go a long way towards explaining why.

What the official guidelines say

• NHS (United Kingdom): aim for steady weight loss of 0.5 to 1 kg a week.
• NICE (United Kingdom, 2025): does not give a rate in kilos. It says that diets of 800 to 1,200 kcal a day should only be used in specialist services. Diets under 800 kcal should only be used when there is a medical reason for rapid weight loss, for up to 12 weeks and with medical supervision.
• US guidelines (2013): they talk about a deficit of 500 to 750 kcal a day, or 1,200 to 1,500 kcal for women and 1,500 to 1,800 for men. They say that steady loss of 3% to 5% of body weight already brings health benefits, and that the greatest loss usually comes at around 6 months.

Why a percentage of body weight

One kilo a week is 1% for someone weighing 100 kg and almost 1.7% for someone weighing 60. For the second person it is much steeper. That is why MesogeaFit measures the rate as a percentage of your weight:

• from 0.25% to 1% a week,
• with 0.5% as the default,
• with an upper limit of 0.7% for people with a body mass index (BMI) under 25 or who lift weights,
• and never more than 1 kg a week, however much you weigh.

The idea comes from sport. A 2014 review for athletes suggests 0.5% to 1% a week so that muscle is not lost. In a small trial of 24 athletes, those who lost weight at 0.7% a week gained muscle mass, while those who lost at 1.4% did not. These are studies in athletes, so for the general population they are of low certainty.

See what this means for your own weight:

How many kilos in a month

A calendar month has about 4.3 weeks, so at 80 kg and 0.5% a month gives about 1.7 kg. These are targets for your weight trend. The daily reading on the scales will go up and down around it.

Why the first week shows more

Your body stores carbohydrate in the muscles and liver as glycogen, and every gram of glycogen holds at least 3 g of water with it. When you eat less, your glycogen goes down and the water leaves. That is why the scales drop faster in the first few days. The mechanism is fairly certain. We don't know exactly how much they will drop for each person, and we did not find a reliable average.

So if you lose 2 kg in the first week, do not expect 2 kg every week. After the first few days the water loss stops and the rate moves closer to your target.

When it is too fast

Gallstones. In a Swedish programme with 3,320 pairs of people, some followed a 500 kcal diet for 3 months and others a 1,200 to 1,500 kcal diet. Over a year, the first group lost more weight, 11.1 kg against 8.1. But they had more than three times as many gallstone cases needing hospital care, 152 against 44 per 10,000 people a year. This is an observational study, so the finding is of low certainty. An older analysis found that the risk rises sharply above 1.5 kg a week.

Muscle. In a trial of 57 adults, a very strict 5-week diet and a gentler 12-week diet gave similar weight loss, about 8 to 9 kg. With the strict diet, however, a larger share of fat-free mass was lost, and those who lost more of this mass regained more weight. The finding is of low certainty.

Is weight lost quickly easier to regain?

This is not certain. In a trial of 200 adults, fast weight loss over 12 weeks and slow loss over 36 weeks led to similar regain after about 3 years, about 71% of the weight lost. The reasons to prefer a slower rate are safety, muscle and how easy it is to keep to.

What the app does

• If you choose a goal date that is very close, the app moves the date later instead of dropping your calories below the safe floor.
• If you lose more than 1.5 kg a week, the app stops the deficit and suggests you talk to a doctor.
• The goal date is shown as a range of months, because nobody loses weight at a perfectly steady rate. The reasons are explained in the article on daily calories.

Who should not diet to lose weight without a doctor

• Pregnant women.
• Minors.
• People with a BMI under 18.5.
• People who have or have had an eating disorder.
• People with type 1 diabetes, or who take insulin, sulphonylureas or SGLT2 inhibitors.
• People with chronic kidney disease stage 3 or above, a kidney transplant, or who don't know their stage.
• People with heart failure or cirrhosis, who are having cancer treatment or who had bariatric surgery in the last 2 years.

For all of them, the app does not create an automatic weight-loss plan. Where it can, it offers healthy eating and weight maintenance, and suggests they talk to their doctor.

During breastfeeding the app allows only a small deficit. It applies from the 8th week after giving birth, if BMI is 25 or more, with up to half a kilo a week and never below 1,800 kcal. If you have a history of gallstones, talk to your doctor before any rapid weight-loss programme.