The calories you log are close enough to show your patterns, but not exact. Food labels are accurate on average. In studies, food records and recalls ran about 12% to 24% lower than what people really ate, and in one test, no wrist device estimated calories burned within 20%. Each number is most useful compared with its own history.

Key takeaways

• Restaurant calorie counts were accurate on average, but about 1 in 5 dishes had at least 100 calories more than stated (Urban et al., 2011).

• Food records came out 18% to 21% lower than what adults aged 50 to 74 actually ate (Park et al., 2018).

• In a 2017 lab test of seven wrist devices, none estimated calories burned within 20% (Shcherbina et al., 2017).

• Tracking food helps many people spot patterns, but it isn't for everyone (Levinson et al., 2017).

How accurate are food labels?

Close, on average. When researchers measured 269 restaurant foods in a lab, the stated calories were right on average, within about 10 calories a portion. But 19% of the dishes had at least 100 calories more than the menu said (Urban et al., 2011). In an earlier study, reduced-calorie restaurant meals came out 18% higher than stated, and reduced-calorie frozen meals 8% higher. The results varied too much to be sure (Urban et al., 2010).

Packaged snacks were closer. Across 24 products, they had 4.3% more calories than their labels, well within the allowed range (Jumpertz et al., 2013).

Food lists in logging apps can hold up too. A 2020 study of one popular app found its calorie values matched a reference database closely, though its sodium figures didn't (Evenepoel et al., 2020).

Why do food logs come out low?

The biggest gap is what never gets written down. Researchers check food records against lab methods that measure how much energy people really use, and most studies find the records come out low, by amounts that vary a lot (Burrows et al., 2019).

A famous older study found people missing almost half of what they ate. That came from 10 dieters who had trouble losing weight, so it doesn't describe most people (Lichtman et al., 1992).

One bright spot: people got the share of their calories from protein about right, even when their totals ran low (Subar et al., 2003). If you're curious about that number, see how much protein you need.

How accurate are calories burned on a watch?

Less accurate than steps or heart rate. In a 2017 lab test of seven wrist devices, none estimated calories burned within 20% (Shcherbina et al., 2017). A review of 60 studies found the error changed with the kind of activity (O'Driscoll et al., 2020). A 2025 review of 56 studies of one popular watch found its heart rate and step counts generally accurate, but its calorie numbers less reliable (Choe and Kang, 2025). There's more on how devices count it in active energy, explained.

So a log that runs low and a burn estimate that may run high or low rarely balance. That's normal, and it isn't a sign that either one is broken.

Why is any calorie target a guess?

Your needs depend on your age, sex, height, weight, activity and life stage, and people with the same profile still differ (NASEM, 2023). Metabolism also slows less with age than most people think. Adjusted for body size and muscle, energy use holds steady from about 20 to 60 and declines after that (Pontzer et al., 2021). A target from an app or a formula is a starting point, and your own history is the better guide. That's the idea behind comparing you to you.

Is tracking food worth it?

It depends on what you want from it. In weight-loss programs, people who tracked more tended to lose more weight, though the authors of one review called the evidence weak (Burke et al., 2011). A later review of digital tracking found the same link in 74% of the results it looked at, in adults with overweight or obesity (Patel et al., 2021). Many people also simply like seeing their patterns.

It isn't for everyone. A review found no clear link between tracking and disordered eating in the general population (Roth et al., 2024). But among patients at an eating disorder clinic, 73% of those who used a calorie app said it had made their illness worse (Levinson et al., 2017). If logging makes you anxious, it's fine to stop. If you've had an eating disorder, talk with your care team before you start.

How to use your numbers well

• Log everything for a few ordinary days, drinks and snacks included, to see your real pattern.

• Compare weeks with weeks, not one day with another.

• Use your logged calories for your eating and your device's calories for your activity, each against its own history.

• Take breaks from logging once you've learned what you wanted to know.

Frequently asked questions

Do I need to log every day? No. A few ordinary days, or a couple of weeks now and then, is enough to see your patterns. Gaps are fine.

Are the calories in my app's food list accurate? Often close. One study of a popular app found its calorie values matched a reference database closely, though sodium was off (Evenepoel et al., 2020). What you forget to log matters more.

Should my logged calories match my calories burned? They rarely will. Food records tend to run low (Park et al., 2018), and burn estimates can miss by 20% or more (Shcherbina et al., 2017).

How Knit shows what you log

When you log food in an app connected to Apple Health, Knit shows your calories and nutrients in the Record tab, under Nutrition. Over a few weeks, you'll see what a typical day looks like for you.