How much weight can you lose in a month of intermittent fasting?

There is no fixed amount, and this site does not make lose-X-by-Y forecasts. The first week's drop is mostly water from stored carbohydrate. After that, the pace depends on the gap between what you eat and what you burn.

Is intermittent fasting better than a calorie deficit?

Intermittent fasting works through a calorie deficit, so the two are not rivals. When calories were matched in trials, adding an eating window gave no significant extra weight loss. Choose whichever way of eating less you can keep up.

Which intermittent fasting schedule is best for weight loss?

Across the 99 trials in a 2025 review, alternate-day fasting came out about 1.3 kg ahead of continuous calorie cutting. The gain showed mostly in trials under 24 weeks. Other patterns, such as eating windows and 5:2, gave similar results to calorie cutting. The best schedule is the one you can stick to.

Can you do intermittent fasting without counting calories?

Yes, if the shorter window leads you to eat less. In a 12-week trial, though, adults who ate freely between noon and 8 pm lost no more weight than those eating three meals a day. If the scale stalls, a week of food notes shows whether you are eating less.

Intermittent Fasting for Weight Loss: What the Trials Show

Intermittent fasting for weight loss works the same way as any diet. You lose weight when you eat fewer calories than you burn, and an eating window is one way to get there. Fewer hours of eating can mean fewer meals and snacks. Trials that matched calories found fasting gave about the same weight loss as cutting calories across the whole day.

Does intermittent fasting work for weight loss?

Yes, at about the same rate as other ways of eating less. The evidence is moderate. Many trials point that way, and the largest review calls it “some indication”. The table sets out four of the main studies.

Study	Who took part	What was compared	Result
NEJM trial, 2022	139 adults with obesity, 12 months	Calorie cutting with an 8-hour eating window, or calorie cutting on its own	8.0 kg vs 6.3 kg lost, a gap that was not significant
TREAT trial, 2020	116 adults, 12 weeks	Eating freely from noon to 8 pm vs three meals a day	No extra weight loss from the window
5:2 style trial, 2011	107 women, 6 months	Two low-calorie days a week (about 650 calories) vs daily calorie cutting	The same weight loss
BMJ review, 2025	99 trials, 6,582 adults	Fasting patterns vs continuous calorie cutting	Broadly similar; alternate-day fasting about 1.3 kg ahead in trials under 24 weeks

So intermittent fasting is good for weight loss when it helps you eat less. A fasting window without a calorie gap, as in the TREAT trial, did not beat ordinary meals.

How does intermittent fasting help you lose weight and burn fat?

During a fast, insulin falls and the liver releases its stored sugar (glycogen). Once that store runs low, the body leans on fat for fuel and starts making ketones. That metabolic switch comes somewhere between 12 and 36 hours after your last meal, depending on what you ate and how active you were.

Burning more fat during the fasting hours does not add up to more body fat lost by itself. In the 2022 NEJM trial, adding the eating window to calorie cutting did not bring a significantly bigger fall in weight or body fat. Over weeks, the total calorie gap is what counts. For some people, the window is a simple way to keep that gap without weighing food.

Intermittent fasting or a calorie deficit?

Intermittent fasting and a calorie deficit are not opposites, because intermittent fasting works through one. Calorie counting sets the amount you eat. Intermittent fasting sets the hours you eat in. When the calories match, the weight loss has matched too in the trials above.

The practical difference is how each one feels to live with. Some people find a fixed window easier than tracking every meal, and others find hunger in the morning harder. You can also combine them by eating a set calorie target inside your window.

How much weight can you lose with intermittent fasting?

In the first week, much of the drop on the scale is water, so early intermittent fasting results overstate fat loss. Each gram of stored carbohydrate carries roughly 3 to 4 grams of water, so using it up takes water with it. By the rough rule of 7,700 calories per kilogram, losing 10 kg of fat in 2 weeks would need a deficit of about 77,000 calories. That is about 5,500 calories a day, more than twice the 2,551 a day burned by the man in the worked example below.

After the first weeks, there is no set intermittent fasting weight loss per week, because the pace depends on your calorie gap. The 7,700 rule roughly fits people with a lot of body fat. For leaner people it overstates the deficit needed for each kilogram lost, and it ignores the body adapting over time. Weight also responds slowly to a change in eating, so straight-line forecasts overstate later months. This site does not publish “lose X by Y” projections for that reason.

Losing a lot of weight (9 kg, or 20 lb, or more) can trigger temporary hair shedding a few months later. Hair usually returns to its normal fullness within 6 to 9 months. Questions about belly fat and visceral fat are separate, because the trials here report total weight and body fat.

How to do intermittent fasting for weight loss

Pick a window you can keep. The fasting calculator turns your last meal and schedule into clock times. On 16:8 with a last meal at 7:30 pm, your fast ends at 11:30 am and your eating window closes at 7:30 pm. You can add the window to your calendar from there.
Set your calories. Enter your details in the TDEE calculator and choose “Lose fat”, or “Maintain” to hold your weight.
Eat enough protein. The adult reference intake is 0.8 g a day for every kilogram you weigh. With regular exercise, the advised range rises to 1.4 to 2.0 g.
Count what you drink. Milky coffees, juice and alcohol inside or outside the window all add calories.
Track weekly averages. Weigh at the same time each day and compare one week’s average with the next.

Here is a worked example. In the TDEE calculator, enter a man aged 35, 180 cm tall and 90 kg (198 lb), who does light exercise. His maintenance comes to about 2,551 calories a day. His fat-loss figure is 2,040, which is maintenance minus 20%, the site’s own rule. Guidelines more often prescribe a deficit of 500 to 750 calories a day. Over two meals in his window, the calculator splits that into about 1,020 calories per meal, with 77 g of protein in each.

The meal plan guide turns targets like these into a week of meals. If the scale stops moving, work through the checks in intermittent fasting not losing weight.

Weight training, exercise and muscle

Exercise adds to the calories you burn, but training on an empty stomach adds nothing extra for fat loss. In a 4-week trial, 20 young women on the same diet did cardio either before or after eating. Body composition changed by a similar amount in both groups. That evidence is early (a small, short trial).

If you lift weights, protein matters more. In a review of strength-training studies, extra protein stopped adding muscle gains at about 1.6 g per kg a day. The evidence for that figure is strong (several human trials agree).

Who should not fast to lose weight

Fasting is not a way to lose weight for everyone. Pregnancy, breastfeeding and being under 18 mean you should not use it unless your doctor or midwife advises it. We advise against fasting to lose weight when your weight is already low or you have had an eating disorder; see a doctor instead. With type 1 diabetes, insulin or a sulfonylurea, do not fast unless your doctor has agreed a plan. If a medicine has to go with a meal, keep it with a meal.

If you are underweight and want to gain weight, intermittent fasting is not the tool for it. For a fast of more than 24 hours, talk to a doctor first.

To start, set your eating window in the fasting calculator and check the calorie figure that goes with it in the TDEE calculator.