Most people will lose weight eating 1,500 to 2,000 calories per day, but your specific number depends on your size, age, sex, and how active you are. The general approach is to figure out how many calories your body burns daily, then eat about 500 fewer than that. A 500-calorie daily deficit translates to roughly one pound of weight loss per week.
That said, the old “cut 3,500 calories to lose a pound” rule is a simplification. Your body adapts as you lose weight, so the math shifts over time. Here’s how to find your starting number and adjust from there.
How to Estimate Your Daily Calorie Needs
Your body burns a baseline number of calories just keeping you alive: breathing, circulating blood, maintaining body temperature. This is your basal metabolic rate, or BMR. The most widely used formula for estimating it is the Mifflin-St Jeor equation:
- Women: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
- Men: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
For a 40-year-old woman who weighs 170 pounds (77 kg) and stands 5’5″ (165 cm), that works out to roughly 1,400 calories just for basic body functions. A 40-year-old man at 200 pounds (91 kg) and 5’10” (178 cm) would land around 1,800.
But you don’t lie in bed all day. Your actual calorie burn, sometimes called total daily energy expenditure, is your BMR multiplied by an activity factor. These factors range from about 1.2 for someone who sits most of the day to 2.0 or higher for someone with a physically demanding job who also exercises intensely. A person with a desk job who works out a few times a week typically falls around 1.4 to 1.6. So that 40-year-old woman with a BMR of 1,400 probably burns somewhere between 1,960 and 2,240 calories on a normal day.
The 500-Calorie Deficit Starting Point
For most people with weight to lose, cutting about 500 calories per day from their total energy expenditure is a reasonable starting point. If that same woman burns roughly 2,100 calories daily, eating around 1,600 would put her in a deficit that produces steady, sustainable loss.
The pace won’t be exactly one pound per week, though. The old rule that 3,500 calories equals one pound of fat has been revised. As the Mayo Clinic notes, that equation doesn’t hold true for everyone because it treats your metabolism as static. In reality, the relationship between calories cut and weight lost changes as your body composition shifts. You’ll typically lose more in the first few weeks (partly water weight) and then the rate slows.
Larger deficits produce faster initial results but are harder to sustain and come with more muscle loss. A deficit of 500 to 750 calories per day is the sweet spot where most people can still eat enough to feel satisfied, get adequate nutrition, and maintain energy for exercise.
Why Weight Loss Slows Down Over Time
Your body doesn’t passively accept a calorie deficit. Within the first week of eating less, your metabolism starts to slow beyond what the loss of body mass alone would predict. Research on this adaptive response found that after just one week of calorie restriction, people burned an average of 178 fewer calories per day than expected. That metabolic dip stayed remarkably consistent throughout the dieting period and even persisted afterward.
The practical effect is significant. For every extra 100 calories per day your metabolism slowed during the first week, people lost about 4.4 fewer pounds over six weeks. Your hormones, thyroid activity, and nervous system all dial down energy output to conserve fuel. This is why a calorie target that produces steady weight loss in month one can lead to a complete plateau by month three.
The fix is recalculating periodically. As you lose weight, your body needs fewer calories to maintain its new size, and your deficit shrinks. The NIH’s Body Weight Planner is a free tool that accounts for these metabolic shifts, giving you a more realistic calorie target and timeline than static formulas. It adjusts for changes in appetite, metabolism, and energy expenditure over time.
Calorie Floors You Shouldn’t Go Below
The Dietary Guidelines for Americans specify that their 1,000 and 1,200 calorie meal patterns are designed for young children, not for adults or older kids. While the guidelines don’t name a single universal minimum for weight loss, the implication is clear: adults generally shouldn’t dip below 1,200 calories (for women) or 1,500 calories (for men) without medical supervision. Going lower makes it very difficult to get enough vitamins, minerals, protein, and fiber from food alone, and it accelerates muscle loss.
If a 500-calorie deficit would put you below those floors, aim for a smaller deficit and add physical activity to widen the gap instead.
Most People Undercount Calories
Even if you calculate a perfect target, eating to it is harder than it sounds. A large study published in The BMJ found that adults underestimated the calorie content of their meals by an average of 175 calories. About a quarter of participants were off by at least 500 calories per meal. People eating at restaurants perceived as “healthy,” like Subway, underestimated by 20 to 25% more than those eating at McDonald’s, likely because the health halo made them less cautious.
This means someone aiming for 1,800 calories a day could easily be eating 2,100 to 2,300 without realizing it. Using a food scale for a few weeks, even if you don’t keep it up forever, recalibrates your sense of portion sizes. Most people are shocked by how small a measured serving of rice, peanut butter, or cooking oil actually looks.
Protein Makes a Calorie Deficit Easier
When you eat less than your body burns, it doesn’t pull energy exclusively from fat. Some comes from muscle, which lowers your metabolism and makes future weight loss harder. Protein intake is the biggest dietary lever you have to minimize that muscle loss.
For active people losing weight, research supports eating 1.6 to 2.4 grams of protein per kilogram of body weight per day. For a 170-pound person, that’s roughly 123 to 185 grams of protein daily. Resistance-trained individuals may benefit from the higher end of that range, up to about 2.7 grams per kilogram. Above 2.4 grams per kilogram, additional protein doesn’t appear to offer further muscle-sparing benefits.
Beyond protecting muscle, protein keeps you fuller for longer than the same number of calories from carbohydrates or fat. If you’re in a 500-calorie deficit and struggling with hunger, shifting more of your remaining calories toward protein (chicken, fish, Greek yogurt, eggs, legumes) often helps more than trying to simply eat less of everything.
Putting Your Number Together
Here’s a quick framework to find your starting calorie target:
- Step 1: Calculate your BMR using the Mifflin-St Jeor formula above, or use an online calculator that applies it for you.
- Step 2: Multiply by your activity factor. Use 1.2 if you’re mostly sedentary, 1.4 to 1.5 if you exercise a few times a week, and 1.6 to 1.75 if you’re active most days.
- Step 3: Subtract 500 calories. Check that the result doesn’t fall below 1,200 (women) or 1,500 (men).
- Step 4: Eat at that level for two to three weeks, tracking carefully, and weigh yourself under consistent conditions (same time of day, same clothing).
- Step 5: Adjust based on real results. Losing 0.5 to 1 pound per week means you’re on track. No change means your estimate was too high, or you’re undercounting intake.
The number you calculate is always an estimate. Your actual metabolism could be higher or lower than any formula predicts, and your calorie tracking will never be perfectly accurate. The real target emerges from what happens on the scale and in the mirror over weeks, not from a single equation. Treat the formula as a starting point, not a verdict.