You may think you know all about calories. Many people have been counting them, cutting them, and adding them up for most of their lives. But when it comes to weight loss, there’s actually still a lot of confusion out there about calorie counting. It turns out that many of the most common beliefs on the subject are really just myths. Here are seven of the most persistent calorie counting myths — plus the facts, straight from experts.

1. All Calories Are Created Equal

Plenty of people believe that as long as they stick to a certain number of calories per day, they’re eating healthy. This myth can get in the way of eating a balanced, nutritious diet. “You cannot compare 100 calories of salmon to 100 calories of soda,” says Samantha Cassetty, RD, former nutrition director of Good Housekeeping, who is based in New York City.

She points out that salmon is loaded with beneficial nutrients, including omega-3 fatty acids and protein — one reason the American Heart Association recommends eating it twice a week — that work really hard to nourish your body. “With soda, it’s the opposite — those calories are working against you,” she says. Not only are they lacking in nutrition, but they are also full of sugar, and drinking them has been associated with an increased risk of obesity and type 2 diabetes, past research shows. “It’s a total mistake to think all calories are the same,” Cassetty says.

2. Celery Has Negative Calories

With only about 9 calories a stalk, per the U.S. Department of Agriculture (USDA), it’s obvious how this myth got started. It’s easy to imagine that the act of chewing celery “erases” enough of those calories to take the food into negative calorie territory. “It’s an idea leftover from another era,” says Cassetty.

Cucumbers, radishes, lettuce, and other water-rich vegetables are also sometimes said to be negative-calorie foods, but just like with celery, it’s nothing more than a myth. “There are no negative calorie foods,” says Cassetty.

Related: What Is the CICO Diet and Can It Really Help You Lose Weight?

3. Calorie Labels Are 100 Percent Accurate

What you see is not necessarily what you get when it comes to calorie information on nutrition labels. “There is leeway for manufacturers,” says Cassetty. In fact, by law, food manufacturers can be up to 20 percent off the mark with this number, according to the U.S. Food and Drug Administration (FDA). That means a product you’re eating that you believe has 200 calories might actually have up to 240 calories. A study published in the journal Obesity investigated the accuracy of nutrition labels andfound that prepackaged convenience meals had 8 percent more calories on average than their labels claimed. That can add up.

4. If You Cut 3,500 Calories You’ll Lose 1 Pound

Overall body size, genetics, sleep, and stress can all complicate this rule because as a body loses weight, the amount of calories it needs to maintain that weight goes down.

The 3,500 calories-equals-one-pound math simply doesn’t account for this. Nor does it take into consideration other factors including gender, changing diet and exercise habits, and poor compliance, according to an article in Today’s Dietitian. Carson C. Chow, PhD, a senior investigator in the mathematical biology section of the National Institutes of Health (NIH), is quoted in the article explaining: “Every 10 calories per day decrease in calorie intake leads to an eventual one-pound loss, but it can take three years to get there.” (You can check out the National Institutes of Health’s Body Weight Planner tool to try this new math out for yourself.) This rule of thumb isn’t quite as appealing to dieters as the 3,500 calorie rule, but it’s more accurate.

5. Your Body Absorbs Every Calorie in a Food

There’s a difference between the number of calories a given food contains and how many calories your specific body absorbs from that food. The number of calories you may assimilate can vary based on the makeup of your gut microbiome, according to research, among other things. In another previous study, researchers from Harvard even discovered that calorie counts can vary between raw and cooked foods. And then there’s the fiber effect. Because your body doesn’t absorb fiber (it’s the indigestible part of plants), the amount a food contains can also affect the calories you actually get. One small study of 18 people, which was published in American Journal of Clinical Nutrition, found that almonds contain more calories than they contribute to a person’s diet. Almonds, in particular, are a source of prebiotic fiber, which we do not absorb, according to previous research.

6. The ‘Calories Burned’ Readout on Your Treadmill or Fitness Tracker Is Accurate

Many calorie counters live and die by the “calories burned” readouts on their exercise equipment and fitness trackers. It’s very common for people to decide to eat an extra snack or have dessert based on a number supplied by their device, says Cassetty. But a study from Stanford University published in May 2017 in the Journal of Personalized Medicine found that wearable fitness trackers are generally off by 27 percent. “That’s a substantial amount. If you’re overestimating your calories burned by that much, it can not only make it impossible to lose weight, it can result in weight gain,” she says.

“People don’t realize when they exercise, they’ll unconsciously decrease other energy spent throughout the day,” says Cassetty. Previous research supports the notion that after exercise people may fidget less, stand less, or take the stairs less often. The body is always compensating, making small adjustments to maintain energy balance below the level of your awareness. “It’s not necessarily something you can control,” says Cassetty.

“People do a really bad job of estimating the number of calories they eat, then they get an inflated idea about how many calories they burned thanks to these devices,” says Cassetty. “You can really end up on the wrong side of that equation.”

7. Counting Calories Is Essential for Losing Weight