That tiny box looks objective and precise, but one quick glance can fool you—especially when sugar, serving sizes, and “daily values” don’t mean what most people think they do.

If you’re like most Americans, you probably read the Nutrition Facts label before buying a food product — but are you sure you’re reading it correctly?

Estimates suggest 1 in 5 people don’t understand it. And even those who think they do may be making common mistakes, experts say.

The label’s simple design “leads consumers to imagine it’s a coherent, simple, objective panel,” said Xaq Frohlich, PhD, author of From Label to Table: Regulating Food in America in the Information Age. “But where the numbers come from are all very different.”

Keep these three things in mind next time you look at the Nutrition Facts.

1. The “Daily Value” percentage isn’t for everyone.

The percentage column helps us grasp whether or not a food might be a good choice. It’s true but tricky. The “% Daily Value” shows what percentage of the recommended intake comes in a single serving. But don’t assume the percentage applies to you.

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That percentage is based on a one-size-fits-all diet of 2,000 calories a day. In reality, your specific needs depend on your age, height, weight, and how much you move. For instance, an active 5’7”, 50-year-old woman needs 2,100 calories per day at 120 pounds, but at 190 pounds it goes up to 2,500, according to the USDA’s intake calculator. A very active, 6-foot, 180-pound man of the same age needs 3,350 calories, while a 35-year-old breastfeeding woman needs 2,600 calories at 5’5” and 170 pounds. Because calorie needs vary so widely, the recommended daily amounts might be far more (or less) than what your body actually needs.

Here’s a broader way to apply those percentages that works no matter how many calories you need each day.

If a food provides 5% or less, it’s low in a particular nutrient.
Once you hit the 20% mark, the food is high in that nutrient.
Most people should seek out foods that are higher in fiber, vitamin D, calcium, iron, and potassium and lower in saturated fat, sodium, and added sugars.

“Let’s say I’m looking at a can of artichokes, and it’s around 20% for sodium,” said Hope Barkoukis, PhD, chair of the nutrition department at Case Western Reserve University School of Medicine. “You can still have it, of course, but realize that choice is a high source. Conversely, it’s got 4% of total carbs. That’s saying it’s a low source.”

2. Those numbers aren’t precise.

That little chart is packed with numbers. Somebody calculated each one, so you might assume they’re exactly right. Surprise! By law, the label has a lot of wiggle room: Nutrients we’re advised to limit, including calories, sugars, saturated fat, and sodium, can be up to 20% higher than what’s on the label. With all other nutrients that exist naturally in a food, the amount can be as much as 20% lower. Only the listings for added nutrients, like you’d find in fortified foods, are required to be precise.

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That leeway is granted because manufacturers can’t control everything. A package of frozen vegetables doesn’t have precisely the same amount of each nutrient every time.

Even that 2,000-calorie baseline and the accompanying Daily Value (DV) get a little fuzzy.

“The people who decided this thought 2,000 was a round number, and people would understand that it was not a precise figure — that it was easy to do math with,” Frohlich said. “It looks like this precise tool, but it’s designed in a way that recognizes that people aren’t precise about how they’re using it.”

The Daily Value stems from two separate sets of data. The Recommended Dietary Allowance (RDA) of a nutrient represents the average amount nearly all healthy people need each day, while the Adequate Intake (AI) is more of an assumption, assigned when there’s not enough research to establish exactly how much we need. On a nutrition label, the DV often — but not always — matches the RDA or AI of a nutrient.

Yes, it’s confusing. No, you shouldn’t take these numbers as a guarantee. As Frohlich pointed out, they were never intended to be. Put down your calculator and think of them in big-picture, ballpark terms like high and low, compare similar products, and you should do just fine.

3. Check both sugar levels.

Sugar content is right there under Total Carbohydrates. But there are usually two sugar entries: Total Sugars and Added Sugars. Unless a health care professional has advised you to count your total sugar grams, it’s the second number that really counts.

“People look at the milk label and say, ‘I can’t drink milk,’” said Joan Salge Blake, EdD, a dietitian and nutrition professor at Boston University and the host of the nutrition & health podcast Spot On! “They don’t understand milk has a natural sugar called lactose. Yes, it has sugar, but no added sugar. This happens even with my nutrition students, who should already know.”

The new Dietary Guidelines for Americans make this distinction and recommend you get no more than 10 grams of added sugar from any one meal.