How much weight do you lose overnight?

You weighed yourself before bed, and this morning the scale says you're a pound and a half lighter. You didn't exercise, you didn't skip a meal, and all you did was sleep. That feels like a small win, until the next morning, when the drop is half the size and you start wondering what went wrong.

Nothing went wrong. A scale weighs everything you're carrying, and a lot of what you carry at bedtime is water on its way out. If you read every morning's number as a verdict on your effort, normal nights start to look like failures. That doubt is one of the ways a good plan falls apart.

This page adds up what leaves your body on a normal night, from urine to water vapor to carbon. Then it covers what changes the total and why your morning weight is still the number worth tracking. For the energy side of the night, see our post on how many calories you burn sleeping.

How Much Weight Do You Lose While Sleeping?

You lose about 710 grams (1.6 pounds) over an ordinary 8-hour night, counting your first trip to the bathroom. A bowel movement brings that to about 825 grams (1.8 pounds). We looked for a study that weighed a large group of healthy adults at bedtime and again after waking, and we couldn't find one that was openly readable. So this table adds up the night from the best open measurements of each route:

A liter of water weighs a kilogram, so milliliters and grams match here. The skin and breath rows assume the daily rates hold overnight, which is an estimate. Sweat you can see isn't in the table, because a cool room produces little of it.

Your own night can sit well away from that total. Overnight urine in the survey averaged 460 mL, but single nights ran from 60 to 1,500 mL. The sample was the general public on a one-day diary, including people with high blood pressure and diabetes. Someone who drinks little in the evening may lose closer to 1 pound, and a larger person in a warm room can lose more than 2.

Timing changes what you see, too. Until you use the bathroom, the night's loss is only about 250 grams, just over half a pound. The urine is still in your bladder, so the scale still counts it.

Why Do You Weigh Less in the Morning?

You weigh less in the morning because water and a little gas leave your body all night while nothing comes in. Our page on how much weight fluctuates in a day shows how meals and drinks build the evening peak. Here's how each overnight route works.

Urine is the biggest share

Your kidneys keep filtering while you sleep, only more slowly. In the bladder diaries, the night's urine came to about a quarter of the 24-hour total, even though 8 hours is a third of the day. A hormone called vasopressin helps by pulling water back into the body and concentrating urine at night (Weiss, 2012). The night's share rose with age in men, from 23 percent under 50 to 33 percent at 60 and over.

Skin and breath lose water you never see

Water moves through your skin all the time, even when you aren't sweating. The National Academies' water report puts that loss at about 450 mL a day, and breath losses at 250 to 350 mL a day for a sedentary adult. A clinical rule of thumb for both together is 0.5 mL per kilogram of body weight per hour (Lizzo and Rout, 2026). That's about 290 mL over 8 hours at 160 pounds, a little above the table's 230 mL, and about 450 mL at 250 pounds. So expect at least a cup of water to leave this way each night, and more in a larger body.

A little carbon leaves, and oxygen nearly cancels it

You do breathe out carbon every night. A sleeper burning 440 calories makes about 150 grams of carbon dioxide over 8 hours, and about 40 grams of that is carbon. But the same sleeper breathes in about 130 grams of oxygen, and the scale counts that too. So gas exchange only takes off the gap between them, roughly 10 to 30 grams.

Those figures are our arithmetic, using the Weir equation and a respiratory quotient of 0.8 to 0.9 (Mtaweh and colleagues, 2018). When you burn mostly fat, the quotient nears 0.7 and the two gases almost cancel. Our page on where fat goes when you lose weight follows the atoms. The scale follows total mass, and the oxygen you breathe in counts as mass.

What Changes How Much You Lose Overnight?

Five things move the overnight number. Nearly all of them act on water, so the effect fades within a day or a few days.

Sleep length

At the table's rates, each hour asleep takes off about 90 grams, or 3 ounces. A 6-hour night comes to about 530 grams and a 9-hour night about 800, before any bowel movement. Short sleep also goes with poorer hydration. In about 20,000 US and Chinese adults, those reporting 6 hours of sleep had 1.59 times (US) and 1.42 times (China) the odds of inadequate hydration on urine tests, compared with 8 hours (Rosinger and colleagues, 2019). That's an association from surveys, so it can't show cause.

Room heat and bedding

Sweat is the biggest wild card and the hardest to put a number on. In a lab study of 17 men, body-mass loss during sleep was highest at 32 °C (90 °F) and 80 percent humidity in still air (Tsuzuki and colleagues, 2008). Moving air cut the loss, and a 26 °C (79 °F) room at 50 percent humidity cut it further, though the published summary gives no gram values. A review from the same research group says mild heat doubled whole-body sweat loss in older men (Okamoto-Mizuno and Mizuno, 2012). Air under your covers usually sits at 32 to 34 °C, so your bedding matters as well as your thermostat.

Salt

A salty dinner can shrink the drop or hide it. In a randomized crossover trial, 70 healthy young men spent seven days each on low-sodium and high-sodium diets (van den Bosch and colleagues, 2021). On high sodium, fluid outside their cells ran about 0.9 liters higher after adjusting for body size, and average weight was 80.6 kg against 79.2 kg. That water leaves over days, as our guide on how to lose water weight explains.

Alcohol

Alcohol's drying effect is smaller than its reputation. In a randomized crossover trial of 20 men aged 60 to 75, about two US standard drinks of wine or spirits with lunch added roughly 70 to 85 mL of urine by two hours (Polhuis and colleagues, 2017). By 24 hours the difference was gone, and beer made no difference at any point. The trial didn't test evening drinking or women, so treat it as a rough guide.

A late meal

A late dinner changes what stays more than what leaves. A review of capsule studies in 1,885 healthy volunteers found that whole-gut transit usually took 23 to 37 hours (Nandhra and colleagues, 2023). So most of the solid part of tonight's dinner will still be inside you tomorrow morning. Skip it and the number looks better by the weight of that food, which returns with your next meal.

Do You Lose Weight When You Sleep?

You do lose weight when you sleep, but almost none of it is fat. Our calories burned sleeping page works out the ceiling: about 50 grams if every calorie of a 440-calorie night came from fat, and real fuel is a mix. That's about 7 percent of a 710-gram drop at the very most. The fat isn't an extra row in the table, either, because its atoms leave through the same breath and water routes. The rest is water you'll replace with breakfast and your morning coffee, which is why the morning low doesn't last.

Can Lack of Sleep Cause Weight Gain?

Yes, short sleep can cause a small weight gain, and it works through the days that follow rather than the overnight drop. A 2026 analysis pooled two randomized crossover trials of 95 adults at elevated cardiometabolic risk (Zuraikat and colleagues, 2026). Six weeks of going to bed 1.5 hours later cost about 78 minutes of sleep a night and raised body weight by 0.45 kg, about 1 pound. Daily calories burned and body fat percentage didn't change, and the authors inferred that people ate more, though intake wasn't measured. Our page on whether 6 hours of sleep is enough covers the appetite research.

Why Morning Weight Is the Useful One

Morning weight is useful because the night clears most of what makes weight swing. After the bathroom and before breakfast, your stomach is close to empty, your bladder is empty and the day's meals and drinks haven't started. Your colon keeps a schedule too. In 24-hour recordings of 14 healthy volunteers, colon activity was minimal during sleep and rose at morning waking (Narducci and colleagues, 1987). That's why a bowel movement often comes soon after you get up, and our page on how much weight you lose when you poop shows what it's worth on the scale.

The best demonstration is one man's bathroom scale. A coauthor of a 2023 paper weighed himself nearly every morning for almost 30 years, undressed, after the bathroom and before food or drink (Schneditz and colleagues, 2023). His weight moved with a standard deviation of 0.53 percent from one day to the next. At 170 pounds, that's about a pound of normal noise, and the paper reports a nearly identical figure in 86 male students.

Now compare that with fat loss. A plan that loses a pound of fat a week loses about 65 grams of fat a day. The overnight drop is about 11 times that, and the day-to-day noise about 6 times. So a single morning can't show fat loss, while an average of your mornings across a week or more can. Our guide on how often to weigh yourself lays out the routine, and one habit keeps the numbers clean: weigh after the bathroom, since a full bladder can change the reading by a pound.

What This Means for You

You'll wake up lighter than you went to bed on nearly every normal night. Enjoy it if you like, but don't score it. A big drop doesn't mean you burned more fat, and a small one doesn't mean you failed.

The number that counts is the trend in your morning weight over weeks, and it only moves if your habits hold. That's where most plans fall apart: you show up Monday, miss Wednesday and skip the next week, and then you blame yourself. Staying consistent is hard, but it doesn't have to depend on willpower. Our comparison of the best fitness apps for staying consistent ranks apps on how well they keep you training.

In FitCraft, 3D AI coaches demonstrate every bodyweight and dumbbell exercise, and your coach calls you by name during the workout. Streaks, leaderboards and a new seasonal quest each month give you a reason to come back, and your workouts adjust as you progress. As Matt put it: "The real win is I actually want to work out now. That's never happened before."