Most people need to eat roughly 500 calories below what they burn each day to lose about one pound per week. That’s the widely recommended starting point from nutrition scientists at the National Institutes of Health, and it translates to a total weekly deficit of about 3,500 calories. But the actual number of calories you should eat depends on your size, age, sex, and how active you are. There’s no single number that works for everyone.
How to Estimate Your Daily Calorie Burn
Your body burns calories in three main ways: keeping you alive at rest (breathing, circulation, cell repair), digesting food, and physical movement. The calories burned at rest, called your resting metabolic rate, typically account for the largest share. The formula most dietitians recommend for estimating it is the Mifflin-St. Jeor equation, which the Academy of Nutrition and Dietetics considers the most accurate option, especially for people who are overweight or obese.
Here’s how it works. You’ll need your weight in kilograms (divide pounds by 2.2) and height in centimeters (multiply inches by 2.54):
- Men: (9.99 × weight) + (6.25 × height) − (4.92 × age) + 5
- Women: (9.99 × weight) + (6.25 × height) − (4.92 × age) − 161
The result tells you roughly how many calories your body burns just existing. To get your total daily burn, multiply that number by an activity factor. The Food and Agriculture Organization of the United Nations breaks these into three tiers: 1.4 to 1.69 for sedentary or lightly active people (desk job, minimal exercise), 1.7 to 1.99 for moderately active people (regular exercise or a physically demanding job), and 2.0 to 2.4 for vigorously active people (intense daily training). Values above 2.4 are difficult to sustain long-term.
For example, a 40-year-old woman who weighs 170 pounds (77 kg) and stands 5’5″ (165 cm) has a resting metabolic rate of about 1,410 calories. If she’s lightly active, her total daily burn lands somewhere around 2,000 to 2,400 calories. To lose a pound a week, she’d aim for roughly 1,500 to 1,900 calories per day.
Why the “500 Calories a Day” Rule Isn’t Perfect
The idea that cutting 500 calories daily equals one pound lost per week comes from a 1958 calculation by scientist Max Wishnofsky. The math is straightforward: one pound of body fat contains roughly 3,436 to 3,752 calories, so a 3,500-calorie weekly deficit should burn one pound. In practice, though, this rule significantly overestimates how much weight you’ll actually lose over time.
The reason is that your body fights back. When you eat less, your metabolism slows down in a process researchers call adaptive thermogenesis. Your body becomes more efficient, doing the same work with fewer calories. You also tend to move less without realizing it. One study found that after just one week of calorie restriction, people’s daily energy expenditure dropped by an average of 178 calories beyond what the loss of body mass alone would predict. That metabolic slowdown remained stable for weeks afterward. For every extra 100-calorie drop in daily metabolism during the first week, participants lost about 4.4 fewer pounds over six weeks than expected.
This means weight loss typically starts fast and then tapers. The 500-calorie rule works reasonably well for the first few weeks, but over months, your actual rate of loss will slow unless you adjust your intake or activity level.
Safe Minimums and Realistic Targets
Aiming to lose one to two pounds per week is the range that NIH researchers consider safe and sustainable. Faster loss is tempting, but gradual weight loss is more likely to stay off. Crash dieting also comes with a hidden cost: up to 25% of the weight you lose can be muscle rather than fat. Losing 100 pounds through aggressive dieting, for instance, could mean losing 25 pounds of muscle along the way.
There’s also a hard floor on how low you should go. Diets under 800 calories per day are classified as very-low-calorie diets and require medical supervision because of the risk of health complications. These aren’t something to attempt on your own. For most women, staying above 1,200 calories and for most men above 1,500 calories provides enough room to get adequate nutrition while still losing weight at a reasonable pace.
Protecting Muscle While Losing Fat
Preserving muscle during weight loss matters because muscle burns more calories at rest than fat does. Losing it slows your metabolism further and makes it harder to keep weight off. Two strategies make the biggest difference.
First, eat enough protein. The recommendation for people actively losing weight is about 1 to 1.2 grams of protein per kilogram of body weight daily. For a 180-pound person, that’s roughly 82 to 98 grams per day. Protein also costs more energy to digest than carbs or fat. Your body uses 15 to 30% of protein’s calories just breaking it down, compared to 5 to 10% for carbohydrates and 0 to 3% for fats. So higher-protein meals give you a small metabolic edge on top of preserving muscle.
Second, exercise consistently. Research shows that aerobic exercise (walking, cycling, swimming) can prevent up to 8% of the muscle loss that typically accompanies dieting, while resistance training prevents up to 20%, as long as you’re doing it three or more times per week. Strength training is the single best tool for holding onto muscle in a calorie deficit.
What You Eat Matters, Not Just How Much
Sticking to a calorie deficit gets dramatically easier when you’re not constantly hungry. Fiber is one of the most effective tools for managing hunger on fewer calories. A study published in the Annals of Internal Medicine found that people who simply aimed to eat 30 grams of fiber per day lost 4.6 pounds and kept it off for 12 months, even without following any other dietary rules. That was only slightly less effective than a comprehensive heart-healthy diet, which produced 5.9 pounds of loss over the same period. Vegetables, beans, whole grains, and fruit are the most practical sources.
Protein also helps with satiety. Because it takes so much energy to digest and keeps you full longer, swapping some refined carbs for protein-rich foods can make a calorie deficit feel less restrictive without changing the numbers.
Adjusting Over Time
The calorie target you start with won’t be the right target three months later. As you lose weight, your body gets smaller and burns fewer calories both at rest and during movement. A person who drops from 200 to 180 pounds may need 150 to 200 fewer calories per day than when they started, just to maintain the same deficit. Recalculating every 10 to 15 pounds lost keeps progress steady.
Plateaus are normal and don’t mean the approach has failed. They usually mean your body has adjusted to your current intake. When progress stalls for more than two or three weeks, you can either reduce calories slightly (by 100 to 200 per day), increase activity, or both. Small adjustments tend to be more sustainable than dramatic cuts, which can trigger stronger metabolic resistance and make the diet harder to maintain.
Tracking your intake for at least a few weeks, using a food scale and an app, gives you a realistic picture of where your calories actually come from. Most people underestimate how much they eat by a significant margin, and closing that gap is often enough to restart progress without changing the target at all.