Celebrities like Terry Crews have popularized intermittent fasting—not eating for lengths at a time—as a weight loss tool.

The practice doesn’t guarantee you’ll drop pounds, but it can help you consume fewer calories—which aides in weight loss.

As a refresher, there are different ways to fast, but people generally follow three common schedules: alternate-day fasting, whole-day fasting, or time-restricted fasting. Melanie Boehmer, R.D. at Lenox Hill Hospital, recommends starting with time-restricted fasting. The 16:8 format, meaning you only eat for eight hours in a day, is popular for this method.

It’s always frustrating when the scale is stuck on the same number—despite your best efforts. If you’ve been fasting and haven’t seen results, it’s a good time to analyze your strategy.

Here are some common reasons that explain why you’re not losing weight from intermittent fasting.

You’re eating too many calories

You want to start a food journal before embarking on any kind of diet, says Melanie Boehmer, R.D. at Lenox Hill Hospital.

“It is helpful to monitor your intake to at least understand what your baseline is,” Boehmer tells Men’s Health.

Track everything you eat in a given week using FitDay.com, Lose It!, or MyFitnessPal.

Then, determine how many calories your body needs to maintain its current weight. This can be done using a formula or the body weight planner by the National Institute of Health.

From there, it’s just a matter of comparing your actual intake to what you need. It goes without saying that you won’t lose weight—regardless of fasting—if you consume too many calories

You underestimate portions

If you’re not losing weight—despite staying within your calorie needs—then it’s time to look at serving sizes. It’s common to miscalculate how much you’re actually eating, which leads to consuming more calories than you think. This is particularly true with calorie-dense foods such as cheese.

For example, a one-ounce serving of full fat cheese equals about four dice. Use a food scale—or eyeball portions with this tutorial—to more accurately calculate food intake.

You’re not eating enough

If you’ve hit a weight loss plateau after losing a few pounds, Boehmer says you may be eating too few calories.

That’s because our bodies adjust to whatever we throw at them, she says.

“If on average you’re only taking in 1200 calories, which is something none of us should be doing on a regular basis, your body is going to learn to function on 1200 calories.”

Reduce calories slowly and aim for more moderate weight loss, says Boehmer. She advises cutting enough calories to lose about a pound a week.

“When we talk about losing weight, the goal is always to lose as much weight eating thee most that you can so you don’t create that metabolic inhibitor,” she says.

Melissa Matthews Health Writer Melissa Matthews is the Health Writer at Men’s Health, covering the latest in food, nutrition, and health.