The science of weighing in

01

Why weigh in more often

People who weigh in often lose more and regain less.

What studies found

• Daily weigh-ins with weekly feedback: 6.6% of body weight lost in 6 months, against 0.4% in a group that waited ^[1].
• A review of 17 studies linked regular weighing with more weight loss ^[2].
• Weight went up during breaks of a month or more ^{[3] [4]}.
• People keeping weight off who weighed in less often regained more ^[5].

What it doesn't show. Most of these studies watched people and tested nothing, so the link may run both ways: people may stop weighing because they're gaining ^[3]. The trial added weekly emails and lessons to the weighing ^[1].

02

How often should you weigh yourself?

At least every 3 days. Every morning, if it stays calm.

What studies found

• In that trial, people weighed in about 6 days a week ^[1].
• 9,768 smart-scale users averaged 2.8 weigh-ins a week ^[3].
• Weighing daily with a chart, and nothing else: 2.6 kg lost in a year, against 0.5 kg ^[6].

What to do

• Pick a time you'll keep, like right after you wake up, and set an alarm for it.
• Missed a few days? Step on tomorrow. The average picks up where you left it.

What it doesn't show. No study has tested every 3 days against more or fewer. It's about the fewest that still gives a 7-day average something to read.

03

How to weigh in

Same scale, same time, same conditions.

What studies found

• Digital bathroom scales were accurate and consistent against certified weights. Dial scales were less so ^[7].
• Weight is higher after the weekend and lower later in the week ^[8].

What to do

• Use a digital scale on a hard, flat floor.
• Step on in the morning, after the bathroom, before you eat or drink.
• Wear the same thing each time, or nothing.
• Once is enough. Stepping on again won't change the day.

What it doesn't show. No study has compared morning weighing with evening weighing. Mornings are simply the easiest time to keep the same.

04

Why one morning lies

A jump overnight is mostly water.

What studies found

• Over two weeks, 84% of the change in people's weight was water and lean tissue ^[9].
• Weight is higher after weekends ^[8].
• It's about 0.5 kg (1 lb) higher during a period, from water ^[10].

What to do

• Salt, carbs, a late dinner and a hard workout all hold water.
• Up after a weekend is normal. Look again midweek.

What it doesn't show. These are group averages. Your own swings may be bigger or smaller.

05

Read the trend

Watch the 7-day average over a week or two.

What studies found

• Your weight follows the gap between what you eat and what you burn, slowly ^[11].
• From weigh-ins alone, a model estimated changes in what people ate within 40 kcal a day on average. For one person, it could be off by around 215 ^[12].

What to do

• Going down over a week or two: you're likely eating less than you burn.
• Flat: about even. Going up: likely eating a bit more.

What it doesn't show. That model used many weigh-ins over two years. A week of home weigh-ins gives a rougher read, which is why steps.org says likely.

06

Should you weigh yourself every day?

For most adults trying to lose weight, yes, it's fine. Watch how it makes you feel.

What studies found

• In adults trying to lose weight, regular weighing wasn't linked with depression, anxiety or disordered eating ^{[2] [13]}.
• A gain on the scale brought guilt, and the guilt made people less likely to stick to their plan that day ^[14].
• In women aged 18 to 22, daily weighing raised weight-related stress and lowered body satisfaction ^[15].

What to do

• Read the number as information about the average, and about nothing else.
• In steps.org, a gain keeps your challenge going just as a loss does. Showing up is what counts.
• If a weigh-in ruins your day, stop, and talk to your doctor.

What it doesn't show. One review also found a small link with lower self-esteem ^[13]. Most of these studies ran for weeks or months, in people who chose to join a weight loss study.

07

Who shouldn't weigh in often

Anyone with an eating disorder, now or in the past, anyone pregnant, and anyone under 18.

What studies found

• People with eating disorders weigh themselves more, and more often say it affects their mood ^[16].
• Teenagers who dieted in unhealthy ways went on to gain more and binge more ^[17].
• The NHS advises against trying to lose weight during pregnancy ^[18].

What it doesn't show. The first two studies watched people, so they can't say weighing caused it.

08

What to do with the number

Average going down? Keep going. Flat? Eat a little less.

What studies found

• More fruit and vegetables, no calorie target: 7.9 kg (17 lb) lost in a year ^[19].
• Plain advice to eat less worked as well as portion tools ^[20].
• Dietitians keep it visual: half the plate vegetables ^[21], portions by hand ^[22].

What to do

• Fill half the plate with vegetables.
• A palm of fish, a fist of fruit.
• Soups, fruit and vegetables fill you for fewer calories.

What it doesn't show. Health services suggest 0.5 to 1 kg (1 to 2 lb) a week ^{[23] [24]}, but a trial found people regained the same share whether they lost weight fast or slowly ^[25].

09

How steps.org helps

steps.org keeps you weighing in.

A 72-hour clock

Each weigh-in gives you 72 hours to the next, with a countdown on screen.

One email if you're late

With 24 hours left and no weigh-in, one email comes, with one of your own reasons in it.

Something to lose

Let the clock run out and your challenge ends. Starting again costs $5 more, and each day you weigh in takes $1 off.

Your average and balance

The 7-day average, read as likely deficit, even or surplus.