How fast can you safely lose weight?

US and UK health agencies put a safe, steady pace at about 1 to 2 pounds (0.5 to 1 kg) a week.^{[1, 2]} The 1998 US clinical guidelines paired that pace with a first goal of losing 10 percent of your weight over about 6 months.^[3] Faster loss may raise the chance of gallstones, but whether it comes back faster is still argued.^{[5, 6]}

What the guidelines say

The numbers line up across agencies. The CDC says people who lose about 1 to 2 pounds a week are more likely to keep the weight off.^[1] The NHS gives the same pace in metric.^[2] The 1998 US clinical guidelines from the National Heart, Lung, and Blood Institute (NHLBI) set it as a recommendation for the first 6 months.^[3]

The NHLBI guidelines from 1998 also scale the pace to body size.^[3] With a BMI of 27 to 35, a cut of 300 to 500 calories a day gives about ½ to 1 pound a week.^[3] With a BMI over 35, a cut of 500 to 1,000 calories a day gives about 1 to 2 pounds a week.^[3] For people who are overweight, the 1998 guidelines say about ½ pound a week may be more fitting.^[3]

An NIH page, drawing on the 2013 US obesity guideline, puts the first target in plain terms: 5% to 10% of your starting weight within 6 months.^[7] The 2026 guideline that replaced it targets at least 5% to 10%, without a time frame.^[20] You can check where your weight sits now with the BMI calculator.

Why the first week looks faster

Part of an early drop on a new diet can be water. Your body stores carbohydrate as glycogen in the liver and muscles, and each part of glycogen is held with three to four parts water.^[8] In a small study of people starting a very low calorie diet, early changes mostly reflected this store, and the authors point to the water it carries as a cause of weight swings while dieting.^[8]

So a big first week does not set the pace for the months ahead. The 1998 NHLBI guidelines note that 1 to 2 pounds a week commonly lasts for up to 6 months.^[3] After that, loss usually slows and weight plateaus, because a smaller body burns less.^[3] Our guide to why the scale gets stuck covers that part.

A pound a week means different things at different sizes

A fixed number of pounds is a bigger share of a smaller body. In this example, one pound a week is 0.5% of a 200-pound body and 0.8% of a 125-pound body.

In a small trial of 24 elite athletes who also lifted weights 4 times a week, one group aimed to lose 0.7% of body weight a week and the other 1.4%.^[9] Lean mass rose 2.1% in the slower group and stayed flat in the faster one.^[9] That was a short trial in athletes, so it says little about people with more weight to lose. Our guide to losing fat without losing muscle goes further.

What three paces look like for one person

Dalia's app offers three paces, 0.5, 1 or 1.5 pounds a week, which it turns into a cut of 250, 500 or 750 calories a day. The app counts the weeks to your goal by dividing the pounds to lose by the pace and rounding up.

Dalia's app never sets a daily target below 1,200 calories. To try your own numbers, use the calorie deficit calculator, or read how many calories to eat to lose weight for the method step by step.

Is faster weight loss regained faster?

This is the disputed part. The 1998 NHLBI guidelines say rapid weight loss is almost always followed by regain.^[3] The CDC still says a gradual pace is more likely to stay off.^[1] Later research has not settled it.

• A 3-year trial. In 200 adults with obesity, a 12-week rapid diet and a 36-week gradual diet both aimed for 15% loss.^[6] More people reached at least 12.5% on the rapid diet: 81%, against 50%.^[6] Among those who finished a 144-week maintenance phase, both groups had regained about the same share of what they lost, 70.5% and 71.2%.^[6]
• A matched-loss trial. In 57 adults, a 500-calorie diet for 5 weeks and a 1,250-calorie diet for 12 weeks gave similar loss, and similar regain after 9 months.^[10]
• Early pace in a lifestyle program. In 262 middle-aged women with obesity, those who lost fastest in the first month had lost the most at 18 months, and did not regain significantly more than the others.^[11]
• A review. Two researchers concluded that a bigger early loss may improve how well weight stays off, when a 1 to 2 year maintenance program follows.^[12]

So the evidence does not show that slow loss protects you from regain. It also does not make fast loss free, as the next section shows. Researchers still disagree, and the CDC and NHS still advise a gradual pace.^{[1, 2]} What helps weight stay off after the loss is covered in the guide to losing weight and keeping it off.

What very fast loss can cost

• Gallstones. Diets that cause fast weight loss may be more likely to lead to gallstone problems than slower ones.^[5] The 1998 NHLBI guidelines also name a possible risk of electrolyte problems.^[3] In the 3-year trial, one person on the rapid diet developed an inflamed gallbladder and needed it removed.^[6]
• Fat-free mass, which includes muscle. In the matched-loss trial, fat-free mass loss was 8.8% in the 500-calorie group and 1.3% in the slower group, by the study's measure.^[10] Losing more fat-free mass was linked to more regain later.^[10] A trial in 42 adults also found better body composition after slower loss.^[13]
• Very low calorie diets. The 2013 US obesity guideline said diets under 800 calories a day belong only in medical settings, with trained staff.^[4]

One week of weigh-ins is a shaky way to judge pace. Our guide to reading the scale shows why weight swings from day to day and how to read a few weeks at once.

When to talk to a clinician