Most people need to eat roughly 500 fewer calories per day than they burn to lose about one pound per week. For many women, that lands somewhere between 1,200 and 1,800 calories daily, and for most men, between 1,500 and 2,200. But those numbers vary widely depending on your size, age, activity level, and metabolism, so a single universal number doesn’t exist.
Why There’s No Single Magic Number
You’ve probably heard the old rule: cut 3,500 calories and you’ll lose one pound. It sounds clean and simple, but obesity researchers now consider it misleading. As Dr. Fatima Cody Stanford, an obesity specialist at Harvard Medical School, puts it, the idea of “a calorie in and a calorie out” for weight loss is “not only antiquated, it’s just wrong.”
The reason is that your body isn’t a static machine. How you burn calories depends on the type of food you eat, your individual metabolism, your hormones, and even the mix of bacteria in your gut. Two people eating the exact same number of calories can have very different outcomes when it comes to weight. That doesn’t mean calories are irrelevant. It means the math is messier than a simple subtraction problem, and you should treat any calorie target as a starting point, not a guarantee.
How to Estimate Your Calorie Needs
The most widely used method for estimating how many calories your body burns at rest is the Mifflin-St Jeor equation. It’s not perfect, but it’s considered the most accurate formula available without lab testing. Here’s how it works:
- 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
This gives you your basal metabolic rate (BMR), the calories your body uses just to keep itself running while you do absolutely nothing. To get your total daily burn, multiply that number by an activity factor: 1.2 if you’re mostly sedentary, 1.375 for light exercise a few days a week, 1.55 for moderate exercise most days, and 1.725 if you’re very active.
As a quick example, a 40-year-old woman who weighs 170 pounds (77 kg), stands 5’5″ (165 cm), and exercises lightly would have a BMR of about 1,404 calories. Multiply by 1.375, and her estimated total daily burn is around 1,930 calories. To lose roughly a pound a week, she’d aim for about 1,430 calories per day. A 40-year-old man at 200 pounds (91 kg) and 5’10” (178 cm) with the same activity level would burn roughly 2,400 calories daily, putting his weight loss target around 1,900.
Calorie Floors You Shouldn’t Go Below
Cutting more calories doesn’t always mean faster results. Harvard Health recommends that women eat no fewer than 1,200 calories per day and men no fewer than 1,500, unless a healthcare provider is directly supervising them. Dropping below these thresholds makes it very difficult to get the vitamins, minerals, and protein your body needs. It also increases the risk of constant hunger, which sets up a cycle of restriction and overeating that makes the whole process harder to sustain.
A safe, sustainable pace is about one to two pounds per week. Faster loss might sound appealing, but NIH nutrition scientist Dr. Alison Brown notes that gradual weight loss is both safer and more likely to stick long term.
Your Body Fights Back: Metabolic Adaptation
One of the most frustrating realities of dieting is that your body adjusts its calorie burn downward when you eat less. This process, called adaptive thermogenesis, means your metabolism drops more than you’d expect based on your weight loss alone. Research has measured this effect at roughly 178 calories per day on average after just one week of calorie restriction, and it tends to persist throughout the dieting period and even afterward.
This is why weight loss often stalls after the first several weeks, even if you haven’t changed anything. Your body is spending less energy on basic functions like temperature regulation, hormone production, and digestion. It’s not a sign that something is wrong. It’s a predictable biological response. But it does mean that the calorie target that worked in week one may need a small adjustment by week eight or ten. When that happens, cutting another 100 to 200 calories per day or adding a bit more activity can restart progress, as long as you stay above the minimum calorie floors.
Protein Makes a Bigger Difference Than You’d Think
When you’re in a calorie deficit, your body doesn’t only burn fat. It also breaks down muscle for energy, which further slows your metabolism and changes your body composition in ways that make regaining weight easier. The best defense is eating enough protein.
A large systematic review found that eating at least 1.3 grams of protein per kilogram of body weight per day can actually increase muscle mass during weight loss, while eating below 1.0 gram per kilogram raises the risk of losing muscle. For practical purposes, that means a 170-pound person should aim for roughly 100 grams of protein per day, and a 200-pound person should target about 118 grams. Higher intakes in the range of 1.2 to 1.6 grams per kilogram have been shown to preserve lean mass and improve body composition across age groups.
This doesn’t require protein shakes or special foods. Greek yogurt, eggs, chicken, fish, beans, and lentils can get you there. The key is spreading protein across meals rather than loading it all into dinner, since your body can only use so much at once for muscle repair.
Putting It All Together
Start by estimating your total daily calorie burn using the formula above, then subtract 500 calories. Check that your target doesn’t fall below 1,200 (women) or 1,500 (men). Within that calorie budget, prioritize protein at roughly 1.3 grams per kilogram of your body weight to protect muscle mass.
Track your weight weekly rather than daily, since water fluctuations can mask real progress. If your weight hasn’t budged in two to three weeks and you’re confident in your tracking, trim another 100 to 200 calories or add 20 to 30 minutes of activity. Expect the first few weeks to show faster results, followed by a natural slowdown as your metabolism adapts. That slowdown isn’t failure. It’s your body recalibrating, and small, patient adjustments will keep you moving in the right direction.