Most people will lose weight steadily by eating 500 to 750 fewer calories per day than their body burns. That typically translates to 1 to 2 pounds of weight loss per week, which the CDC identifies as the pace most likely to stick long term. But the exact number you need depends on your size, age, sex, and how active you are, and it shifts as you lose weight.
How Your Body Burns Calories
Your total daily calorie burn has three parts. The biggest chunk, roughly 60% to 70%, is your resting metabolic rate: the energy your body uses just to keep you alive (breathing, circulating blood, maintaining body temperature). Another 10% goes to digesting food. The remaining 15% to 30% comes from physical activity, and most of that isn’t formal exercise. It’s walking to the car, fidgeting, standing while cooking, climbing stairs. This category of movement, sometimes called non-exercise activity thermogenesis, varies enormously from person to person and even season to season. People are roughly twice as active in summer compared to winter, and elderly adults show about 29% less of this incidental movement than younger people.
All three components together make up your total daily energy expenditure. To lose weight, you need to consistently eat fewer calories than that total. The size of that gap, your calorie deficit, determines how fast you lose.
Estimating Your Personal Calorie Needs
The most widely validated formula for estimating resting metabolic rate is the Mifflin-St Jeor equation. It uses your weight in kilograms, height in centimeters, and age in years:
- Men: (9.99 × weight) + (6.25 × height) – (4.92 × age) + 5
- Women: (9.99 × weight) + (6.25 × height) – (4.92 × age) – 161
For a 40-year-old woman who weighs 170 pounds (77 kg) and stands 5’5″ (165 cm), that works out to about 1,413 calories per day just at rest. A 40-year-old man at 200 pounds (91 kg) and 5’10” (178 cm) would get roughly 1,828 calories at rest.
To estimate your total daily burn, you multiply that resting number by an activity factor. Someone with a desk job and no exercise routine might multiply by 1.2. A moderately active person (light exercise a few times a week) would use 1.4 to 1.5. Very active people might go as high as 1.7 or 1.8. So that same 40-year-old woman with a moderately active lifestyle would burn around 1,980 calories per day total. Her target for steady weight loss at a 500-calorie deficit would be roughly 1,480 calories daily.
Why the “3,500 Calories Per Pound” Rule Falls Short
You’ve probably heard that cutting 3,500 calories equals one pound of fat loss. That number comes from the energy stored in a pound of body fat, and it’s roughly correct as a snapshot. The problem is that it assumes your body keeps burning calories at the same rate no matter how long you diet, which it doesn’t. Researchers have called this the most serious error of the rule: it fails to account for how your energy balance changes over time, leading to exaggerated predictions with no plateau.
In reality, a 500-calorie daily deficit might produce close to a pound per week in the first few weeks, then gradually slow. Dynamic models that account for your body’s adjustments give much more accurate projections. The practical takeaway: expect faster results early and slower results later, and don’t assume something is wrong when weight loss decelerates.
How Your Body Fights Back Against Calorie Deficits
When you eat less, your body doesn’t just passively burn through its fat stores. It actively lowers its energy expenditure beyond what you’d expect from simply being smaller. Research on overweight subjects found that after just one week of calorie restriction, daily energy expenditure dropped by an average of 178 calories more than the loss of body mass alone would predict. That metabolic slowdown persisted even after six weeks of dieting and a week of eating at maintenance.
This response is remarkably consistent within individuals. People whose metabolism dips the most in week one tend to keep that same pattern throughout the diet. For every extra 100 calories per day of unexpected metabolic slowdown, people lost about 2 kg (4.4 pounds) less over six weeks than predicted.
Hormones play a central role. As you lose fat, your levels of leptin (a hormone that signals fullness) drop, while ghrelin (which drives hunger) rises. Other gut hormones that promote satiety also decrease during weight loss. Meanwhile, brain chemicals that stimulate appetite ramp up. The net effect is that you feel hungrier while burning fewer calories, a combination that makes sustained dieting progressively harder. This isn’t a willpower failure. It’s your body’s hardwired response to perceived energy scarcity.
Setting a Safe Calorie Target
A daily deficit of 500 to 750 calories is the range recommended by most obesity guidelines, and it typically lands people in the range of 1,200 to 1,500 calories per day for women and 1,500 to 1,800 for men. Those lower bounds matter: women generally should not eat fewer than 1,200 calories per day, and men should not go below 1,500 without medical supervision. Below those thresholds, it becomes very difficult to get adequate nutrition, and the risk of muscle loss, nutrient deficiencies, and metabolic disruption rises sharply.
If your calculated deficit would put you below those minimums, a smaller deficit combined with more physical activity is a safer approach. Adding movement increases your total daily burn without requiring you to eat dangerously little.
What Happens When Weight Loss Stalls
Nearly everyone who diets long enough hits a plateau. The primary driver is adaptive thermogenesis: your resting energy expenditure drops to match your lower calorie intake. Your smaller body also burns fewer calories during everyday movement simply because there’s less of you to move. These two factors together can erase your original deficit entirely.
When this happens, you have a few options. You can modestly reduce calories further (as long as you stay above the safe minimums), increase your activity level, or both. Protein intake matters here. Higher-protein diets help preserve muscle mass during weight loss, improve feelings of fullness, and may partially offset the metabolic slowdown. Rather than making dramatic cuts, small adjustments of 100 to 200 calories tend to be more sustainable and less likely to trigger an even stronger metabolic backlash.
Practical Steps to Find Your Number
Start by estimating your resting metabolic rate with the formula above, then multiply by your activity factor to get your total daily burn. Subtract 500 calories from that number. This is your starting target. Track your weight over two to three weeks. If you’re losing about a pound a week, your estimate is in the right range. If nothing is changing, your actual expenditure is probably lower than you calculated, and you’ll need to adjust down by another 100 to 200 calories or increase movement.
Keep in mind that daily weight fluctuates by 2 to 4 pounds due to water retention, sodium intake, and digestive contents. Weekly averages are far more useful than any single morning reading. And as you lose weight, recalculate every 10 to 15 pounds. The calorie target that created a deficit at 200 pounds won’t create the same deficit at 175.
Your non-exercise movement also tends to drop unconsciously during a diet. People move less, fidget less, and take fewer steps without realizing it. Paying attention to daily step counts and general activity levels can help counteract this hidden reduction in calorie burn that quietly shrinks your deficit over time.