In a dream world, wine wouldn’t have calories, chocolate would count as a vegetable, and you could eat what you want, while maintaining a healthy weight. Unfortunately, the reality is that calories add up quickly—sometimes in a single takeout meal. And when you’re constantly bombarded with cues to eat, from tempting TV ads to unlimited office treats, it can seem like the world is sabotaging your efforts. But understanding how many calories you really need, and learning to spot where they’re coming from, is the first step toward achieving a healthy weight.

When the FDA updated the nutrition labels, they needed a nice round number to compare percent daily values to, so they chose 2,000 calories. It’s a rough average and not meant to be a recommendation for how many calories to eat. Although, on average, Americans eat 2,500 calories a day, so if everyone did eat 2,000 calories, the national weight might come down! But because you’re an individual, not an average, 2,000 calories a day probably isn’t the exact right number for you. View it as an easy way to understand food labels and a starting point to calculate your personal needs.

The number of calories you need depends on your weight, height, age, gender, and activity level. There are a few ways you can work it out. The most accurate (and expensive!) way is to get into an insulated chamber to measure how much heat your body is producing. A much simpler way is to put your personal data into an calorie calculator. (Make sure you don’t overestimate how active you are—a mistake many people make!) Personal needs differ massively: If you’re a 6-foot-tall male olympic swimmer, you might need an outrageous 10,000 calories a day, but if you’re a 50-year-old woman and working in an office, you might only need a modest 1,800 calories a day.

When it comes to weight loss, what you eat (“calories in”) is more important than how much you exercise (“calories out”). Tracking calories is still the best way to get to know your numbers. Of course, nobody enjoys the tedium of recording every sip and morsel! But you’ll identify patterns and habits that may be holding you back from your weight loss goals, quickly spotting those excess calories from, say, weekly happy hours, daily candy bars, and pre-dinner crackers and cheese.

Try the food logging feature in the Fitbit app for at least three days (including one weekend day) to get a sense of how many calories you’re typically eating. Then come up with a new “calories in” goal to meet your weight goal. As a general guide, that should be 500 to 750 calories less than the average you logged for those first three days, but pick a reasonable number that you can stick to. Continue to log your food for a few weeks so you can track how closely you’re coming to your new calorie goal. When it comes to weight loss, consistently eating roughly the same amount of calories is key.

You might have heard of the 3,500-calorie principle—eat 3,500 calories less per week (or 500 calories less per day) to lose 1 pound. Unfortunately, it’s an oversimplification. Why? Because, again, everyone’s needs are different, and everybody’s metabolism responds to changes in their diet in a different way! However, if you cut 500 calories a day, you’ll almost certainly lose weight. It might not be exactly 1 pound each week, but the numbers on the scale will start going down. Then to keep dropping, you’ll need to continue to monitor your calories and weight, and make adjustments to what you’re eating as your weight and metabolism changes.

Want to lose more weight, fast? There are a lot of weight loss programs out there that claim you’ll drop a significant number of pounds in just one week. And many of them seem promising at first glance. But rest assured, if something seems too good to be true, it almost always is. Cutting calories too much won’t deliver lasting weight loss results.

The lowest I’ll let clients slash their calories is 1,200 to 1,500 calories per day for women, 1,500 to 1,800 calories for men. Dipping below 1,200 calories is not a good idea—not only is it extremely difficult to maintain, but your basic metabolic needs won’t be met, and all you’ll end up with is a slowed metabolism. Not to mention disappointment when you’re not able to continue to eat so little, and the weight creeps back on. Sure, you might lose weight quickly in the first few weeks on a starvation diet, but it’s mostly just water weight. Stick with a more realistic low-calorie goal, and after the initial drop, aim for a slow and steady pace of no more than 2 pounds per week. At this rate, you’ll be more likely to stick to your new eating habits, and keep the weight off for good.

Once you understand how many calories you really need, and compare it to how much you’ve actually been eating, you will be empowered with real numbers and can start making lasting changes. You don’t need to keep a food log forever! But doing the math might force you to be more mindful, considering everything you put in your mouth, and allow you to reconnect with when you naturally feel hungry and full. Also, remember that what you eat is as important as how much you eat. Choose foods that nourish your body because of the nutrients they contain, not the calories they don’t. And unless you’re a serious athlete, view any exercise you do as an added bonus, not an excuse to chow down on more calories. Anyone who’s started going to the gym in the hopes of losing weight, but failed to change their eating habits, can attest to that!