How much weight can you lose in a month? The real figure for your weight

The useful question is not “how much can I lose?” but “how much can I lose without suffering and without it coming back?”. The answer fits in a table, with two warnings: the first month is misleading, and the following ones go a little slower.

The figure: 0.5% to 1% of your weight a week

Talking in percentages rather than fixed kilos makes sense: with the same relative effort, a 120-kg person loses twice as many kilos as a 60-kg one, and the Hall model (Lancet, 2011) confirms that, for the same calorie cut, people with more fat lose more weight. The 0.5-1% weekly range was proposed by Helms and colleagues (2014) for natural bodybuilding competitors, to lose fat while keeping as much muscle as possible; in fixed amounts, the CDC talks about 1-2 pounds a week (0.45-0.9 kg), which is about 2-4 kg a month. A month has about 4.3 weeks:

*Worked out with the classic rule of about 7,700 kcal per kilo; it is a starting figure, not a guarantee (we explain why below). Two nuances: if you are close to your goal weight, or already lean and training, aim for the low end of the range; and if the deficit takes you below about 1,200 kcal a day (women) or 1,500 (men), choose a slower pace, because eating less than that without supervision is hard to do well. Work out your expenditure with the TDEE calculator; we explain it with examples in caloric deficit for beginners. And if you are not sure how much weight you have to lose, start with your BMI.

Why the first month drops more (and not all of it is fat)

The first weeks of any diet are misleading. When you eat less, especially fewer carbohydrates, your body draws on its glycogen stores, and glycogen is stored with three to four parts water (Kreitzman, 1992). As it partly empties, that water leaves with it: that is why the scale can show 1-2 kg in the first days that is not fat, and why you seem to “regain” a kilo overnight after a weekend with more pasta or more salt. It is water, not fat, in both directions.

The 7,700-kcal rule: useful to start, optimistic for the month

The rule says each kilo lost equals about 7,700 kcal of deficit (3,500 kcal per pound). It is fine for choosing a starting point, but it assumes the deficit stays the same the whole time, and it does not: a lighter body burns less. What the studies say:

• It falls short even over one to three months. Thomas and colleagues (2013) compared the rule with seven experiments in which food intake was controlled (103 adults, 31 to 93 days): on average they lost 9.1 kg when the rule predicted 12.5 kg, about 27% less.
• The slowdown is gradual but steady. According to the Hall model (2011), every 24 kcal of permanent daily cut eventually lowers weight by about 1 kg, and weight takes around a year to cover half the distance to its new balance. Put the other way round: each kilo lost lowers your expenditure by about 24 kcal a day on average.
• People with more fat lose more for the same cut (Hall, 2011): that is why the first months for someone at 110-120 kg can go considerably faster than for someone at 65 kg.

To avoid doing the maths by hand, the weight loss calculator tells you which week you would reach your goal, taking that slowdown into account.

Can you lose 5 or 10 kilos in a month?

Let us do the maths with the same rule. Losing 5 kg of tissue in 30 days would take a deficit of about 1,280 kcal a day (5 × 7,700 ÷ 30); losing 10 kg, about 2,570 kcal a day, more than many people burn in total. So:

• 5 kg in a month is possible on the scale for someone fairly heavy who is just starting, counting the early water; for most people, a large share of those kilos will not be fat.
• 10 kg in a month is not fat: it is water, glycogen and gut content, and it comes back as soon as you eat normally. Diets that promise it are usually very low in calories, which guidelines reserve for settings with medical supervision.
• If you want to lose 2 kg a month, the maths is kinder: a deficit of about 510 kcal a day.

Does losing weight fast make you regain more?

It is the most repeated belief, and the best trial that has tested it does not support it. In the study by Purcell and colleagues (The Lancet Diabetes & Endocrinology, 2014), 200 adults with obesity were randomly assigned to a rapid 12-week programme or a gradual 36-week one, both aiming at a 15% weight loss. 81% of the rapid group and 50% of the gradual group managed to lose at least 12.5%. And at 144 weeks (almost 3 years), both groups had regained practically the same: around 71% of what they lost. Speed on its own does not decide the rebound; what happens afterwards does. We explain it in the rebound effect: how to avoid it.

That does not mean going fast comes free. This is what trials have measured:

• In lean people who train, going slowly protects muscle better: in 24 elite athletes, those aiming to lose 0.7% of their weight a week gained 2.1% of lean mass, while those aiming for 1.4% did not (Garthe, 2011).
• In postmenopausal women with obesity, severe restriction (65-75% less energy for 4 months, with meal replacements) led to 6.6 kg more weight loss over a year than a moderate one, with lean-mass loss proportional to the weight lost, but also more bone density lost at the hip (Seimon, 2019). That is why the authors urge caution in people with osteopenia or osteoporosis.
• Very-low-calorie diets are done under supervision: in the Purcell trial, one person in the rapid group developed gallbladder inflammation that ended in surgery.
• And the practical side: a moderate deficit leaves room to eat enough protein, to train and to keep it up for weeks without going hungry.

How to tell whether you are on the right pace

• Weigh yourself at the same time several days a week and compare one week’s average with the next; a single day’s figure tells you nothing.
• Do not judge your pace by the first two weeks: they carry water.
• If, once past the start, the average drops more than 1% a week for several weeks, you are probably going faster than you will be able to sustain.
• If it has not moved in 3-4 weeks, recalculate: you may be eating more than you log, or your expenditure may have dropped. With the TDEE calculator you can estimate your real expenditure from what you eat and your weight.
• Measure your waist once a month too: sometimes it goes down even when the scale is stuck.

Forget “10 kilos in a month”. 0.5-1% of your weight a week is an honest figure; the first month will drop more because of water and the following ones a little less, and that is normal. What decides whether the kilos stay off is not speed, but the habits you keep afterwards.