Stepping onto a scale can be a nerve-wracking experience. It shouldn’t be, but the truth of the matter is that for many women, it is. Whether or not you’re trying to lose weight, seeing those numbers change can shake you up. We’ve been taught to bow down to the scale and take its word. It knows the big secret of how much we weigh. Your scale, though, might not be so trustworthy. It’s almost always not telling the whole story.

While weight can be helpful in determining whether you might be at a heightened risk for certain diseases and can help your doctor check off all the right boxes to ensure you’ve got a clean bill of health, it’s not the be-all and end-all. In fact, a scale only gives you part of the story. And through lying by omission, it can send mixed messages about your health.

Here are four lies your scale might be telling you.

1. You gained weight overnight.

Your scale may suggest you’ve put on a few pounds after eating that humungous Chinese takeout meal for two you downed yourself (it happens), but you can’t gain actual weight that quickly. Chances are the extra lbs are just water—which your body holds onto when you’re dehydrated, eating too much sodium, or menstruating, among other various reasons. You could even just be constipated, so that extra “weight” is really just from what’s backed up in your bowels.

2. You’re “too heavy” or “too light” based on BMI.

BMI, or body mass index, is a number based off your weight and height. It’s meant to measure body fatness, and depending on your number, you’ll either fall into the normal, underweight, or overweight range. The problem is that BMI really just measures excess weight compared to height—not actual body fat. “BMI does not take into account what your body is made of,” Jackie Baumrind, M.S., R.D., C.D.N., a dietitian at Selvera Wellness, tells SELF. “It cannot differentiate between muscle and fat—for example, if you have two people who weigh 250 pounds and one is a body builder and one is 250 pounds of fat mass” they could have a similar BMI. But their body composition is very different, so one may need to address it while the other has no health risks. The CDC notes a few other flaws with the BMI calculation: It doesn’t consider bone mass, or tell you anything about the distribution of fat on a person’s body. Fat accumulated in the midsection specifically signifies a higher risk of some metabolic diseases. BMI levels do correlate with body fat and future health risks, the CDC adds, so it’s not a totally useless measure. It’s just not the whole story, and, for some people, can be a total throwaway.

3. Working out isn’t working.

Sometimes, you gain weight even though you’re losing fat, slimming down, and clearly putting on lean muscle. Recently, fitness fanatics have been posting their weights alongside before/after progress pics to prove that we should focus on what we look like and how we feel, not numbers on a scale, for this exact reason. Muscle doesn’t actually weigh more than fat, but it’s denser. That means more muscle than fat can be packed into an identical cubic area, making the muscle heavier. Therefore, burning fat and replacing it with muscle on our bodies can result in us looking slimmer and more toned even though the number on the scale increases.

4. Your weight even matters.

“Weight on scale can help when looking at an overall change, but it’s not good to get caught up in day-to-day fluctuations as hormones, menstrual cycle, fluid, salt, alcohol, airplane travel, and medications (just to name a few) can all factor in,” Baumrind says. Weight can fluctuate a few pounds every day, depending on the person, for all of those reasons. “Some people have heart conditions that make fluctuations in weight very serious,” Baumrind adds, but for others, it’s completely inconsequential. And knowing the number has changed is just an unnecessary source of anxiety. “Weigh ins daily are very helpful for some people because it keeps them accountable to themselves and their goals, where for others it becomes an unhealthy obsession.” If you know you’re in a healthy range and have had recent confirmation that your blood pressure, cholesterol, and other standard markers of cardiovascular health are in a good place and that you’re not at risk for metabolic diseases like type 2 diabetes, the number on the scale isn’t all that important.