Most people lose weight steadily on a deficit of 500 calories per day below their total daily energy expenditure, which typically works out to roughly 1,500 to 2,000 calories eaten per day for women and 2,000 to 2,500 for men. But the right number for you depends on how much energy your body burns at rest, how active you are, and how aggressively you want to lose weight without running into problems.
How Your Body Burns Calories
Your total daily energy expenditure has three main components. The largest is your resting metabolic rate, the energy your body uses just to keep you alive: breathing, circulating blood, maintaining body temperature. This accounts for 60 to 70 percent of everything you burn in a day. The thermic effect of food, the energy it takes to digest and absorb what you eat, adds roughly 10 percent. Physical activity makes up the rest, ranging from about 15 percent in sedentary people to as much as 50 percent in highly active individuals.
Within that physical activity slice, a surprising amount comes from movement you don’t think of as exercise: fidgeting, walking to the kitchen, standing while you talk on the phone, even maintaining posture. This non-exercise activity can vary by 350 calories per day or more between people, which partly explains why two people of similar size can have very different calorie needs.
Estimating Your Maintenance Calories
Before you can create a deficit, you need a reasonable estimate of how many calories keep your weight stable. The most accurate formula for this, according to the Academy of Nutrition and Dietetics, is the Mifflin-St. Jeor equation. It predicted resting metabolic rate within 10 percent of lab-measured values in 70 percent of people tested. Here’s how it works:
- Men: (9.99 × weight in kg) + (6.25 × height in cm) − (4.92 × age) + 5
- Women: (9.99 × weight in kg) + (6.25 × height in cm) − (4.92 × age) − 161
That gives you your resting metabolic rate in calories per day. To get your total daily expenditure, multiply 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 for heavy daily training. The result is roughly how many calories you burn in a full day, and the number you’ll subtract from to create your deficit.
For a quick example: a 35-year-old woman who weighs 75 kg (165 lbs), is 165 cm (5’5″), and exercises moderately would have a resting metabolic rate of about 1,417 calories. Multiplied by 1.55, her estimated daily burn is around 2,196 calories. That’s her starting point.
How Big Your Deficit Should Be
A daily deficit of 500 calories produces roughly half a pound to one pound of weight loss per week. The CDC recommends aiming for 1 to 2 pounds per week as the pace most likely to result in keeping the weight off long term. For the woman in the example above, a 500-calorie deficit would mean eating about 1,700 calories per day.
If that feels too aggressive, a smaller deficit of 250 to 300 calories still produces measurable results, just more slowly. This approach works well if you’re already relatively lean, find larger deficits hard to stick with, or want to maintain performance in the gym. On the other end, deficits larger than 500 calories per day are harder to sustain and come with a greater risk of muscle loss, fatigue, and hormonal disruption.
The old rule that 3,500 calories equals one pound of fat is a useful rough guide, but real-world weight loss is rarely that linear. Your body adapts as you lose weight, which means the same deficit produces less loss over time.
Why Your Calorie Needs Drop as You Diet
One of the most important things to understand about a calorie deficit is that your body fights back. When you maintain a weight loss of 10 percent or more, your total daily energy expenditure drops by roughly 20 to 25 percent. Part of that is simple physics: a smaller body burns less fuel. But 10 to 15 percent of the drop goes beyond what the change in body size would predict. Your metabolism genuinely slows down.
In practical terms, someone who has lost significant weight may need 300 to 400 fewer calories per day than a person of the same size who was never heavier. Your thyroid hormone output decreases, your nervous system shifts toward conservation mode, and your muscles become more efficient, burning fewer calories to do the same work. Even your subconscious movement patterns change: people in a deficit tend to fidget less, move more slowly, and sit more often without realizing it.
This is why the calorie target you start with won’t be the one you finish with. Expect to recalculate every 10 to 15 pounds of loss, or roughly every couple of months.
Calorie Floors You Shouldn’t Go Below
Average daily needs sit around 2,500 calories for men and 2,000 for women before any deficit is applied. Most nutrition professionals recommend that women avoid dropping below 1,200 calories per day and men below 1,500. Going lower than that makes it very difficult to get adequate vitamins, minerals, and fiber from food alone, and sharply increases the risk of muscle loss.
If your calculated deficit would put you below those floors, the better strategy is to increase your activity level rather than eat less. Adding a 30-minute walk burns roughly 150 to 200 calories and widens your deficit without cutting food further.
Warning Signs Your Deficit Is Too Aggressive
Calorie restriction triggers real hormonal shifts. Thyroid hormone output drops, cortisol (a stress hormone) rises, and reproductive hormones decline. In moderate deficits, these changes are mild and reversible. In severe or prolonged deficits, they become noticeable.
Watch for persistent fatigue that doesn’t improve with sleep, unusual hair loss, loss of menstrual periods in women, constant irritability, feeling cold all the time, or a dramatic stall in weight loss despite consistent effort. Any of these suggest your body has shifted into a strong conservation state, and eating slightly more, not less, is usually the fix.
Protein Matters More in a Deficit
When you’re eating fewer calories than you burn, your body doesn’t just pull from fat stores. It also breaks down muscle tissue for energy, especially if protein intake is low. The recommended intake during weight loss is about 1 to 1.2 grams of protein per kilogram of body weight per day. For a 75 kg person, that’s 75 to 90 grams daily, spread across meals.
Higher protein intake does double duty: it preserves muscle mass and increases satiety, making the deficit easier to tolerate. Protein also has a higher thermic effect than carbohydrates or fat, meaning your body burns more calories digesting it.
Putting It All Together
Start by estimating your total daily expenditure using the Mifflin-St. Jeor equation and an activity multiplier. Subtract 300 to 500 calories from that number to find your daily intake target. Make sure the result doesn’t fall below 1,200 calories for women or 1,500 for men. Prioritize protein at 1 to 1.2 grams per kilogram of body weight. Track your weight over two to three weeks to see if the rate of loss matches expectations, since no formula is perfect and real-world results are the best feedback loop. If you’re losing faster than 2 pounds per week or experiencing warning signs, eat a bit more. If you’re not losing at all after three consistent weeks, shave off another 100 to 200 calories or add more daily movement.
Weight loss is a moving target. The number you eat today will need to change as your body changes, and the most effective deficit is one you can maintain for months without white-knuckling through every meal.