Setting a calorie deficit means eating fewer calories than your body burns each day, forcing it to tap into stored energy for the difference. The most widely recommended target is a deficit of 500 to 750 calories per day, which produces steady fat loss without the misery of extreme restriction. Getting there involves three steps: estimating how many calories you currently burn, subtracting a reasonable amount, and adjusting over time as your body adapts.
Step 1: Estimate Your Maintenance Calories
Your maintenance calories, sometimes called your total daily energy expenditure (TDEE), represent the number of calories your body uses in a full day including all movement and digestion. It has two parts: your basal metabolic rate (BMR), which is the energy your body needs just to keep you alive at rest, and an activity factor that accounts for everything else you do.
The Mifflin-St Jeor equation is the most commonly recommended formula for estimating BMR:
- 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 35-year-old woman who weighs 75 kg (about 165 lbs) and stands 165 cm (5’5″), the math works out to roughly 1,434 calories per day at complete rest. That number only covers breathing, circulating blood, and maintaining body temperature. To get your actual daily burn, you multiply BMR by an activity factor:
- Sedentary (desk job, little exercise): BMR × 1.2
- Lightly active (exercise 1–3 days per week): BMR × 1.375
- Moderately active (exercise 3–5 days per week): BMR × 1.55
- Active (exercise 6–7 days per week): BMR × 1.725
- Very active (hard daily exercise or physical job): BMR × 1.9
Using the example above, that same woman with a lightly active lifestyle would have an estimated TDEE of about 1,970 calories per day. That’s her starting point. Most people overestimate their activity level, so if you’re unsure, start with the lower multiplier and adjust based on what actually happens on the scale over two to three weeks.
Step 2: Choose Your Deficit Size
A daily deficit of 500 to 750 calories is the range recommended by most obesity guidelines. At the lower end, you can expect to lose roughly one pound per week. At the higher end, closer to a pound and a half. These are averages, not guarantees, and they depend heavily on your starting weight and how consistently you hit your target.
You may have heard the old rule that 3,500 calories equals one pound of fat. Research has shown this significantly overestimates actual weight loss, especially over longer timeframes. The rule ignores the fact that your metabolism slows as you lose weight and that early losses include water and glycogen, not just fat. It’s a rough reference point, but don’t hold yourself to it as a prediction. The National Institutes of Health offers a free body weight simulator (bwsimulator.niddk.nih.gov) that accounts for these metabolic changes and gives more realistic projections.
For most people, a 500-calorie daily deficit is the sweet spot. It’s large enough to produce visible progress within a few weeks but small enough that you’re not constantly hungry or low on energy. Going much beyond 750 calories per day increases the risk of muscle loss, nutrient deficiencies, and the kind of fatigue that derails consistency.
Calorie Floors to Respect
Regardless of your deficit target, there are practical minimums. The Dietary Guidelines for Americans estimate that even sedentary adult women need at least 1,600 calories per day, and sedentary adult men need at least 2,000. Dropping below 1,200 calories for women or 1,500 for men without medical supervision often means you can’t get adequate nutrition from food alone. If your calculated deficit would push you below those floors, use a smaller deficit and add more physical activity to widen the gap instead.
Step 3: Build Your Plate for the Deficit
The total number of calories you cut matters far more than where those calories come from. In one controlled trial, researchers provided all meals to participants and compared a low-fat diet (60% carbs, 20% fat) against a low-carb diet (60% fat, 20% carbs), both set at a 500-calorie daily deficit. Both groups lost the same amount of weight, around 7 to 8% of their starting body weight over eight weeks. The calorie deficit did the work, not the macronutrient ratio.
That said, protein deserves special attention. When you eat less than you burn, your body doesn’t exclusively pull from fat stores. It also breaks down muscle, especially if protein intake is low. Research on adults losing weight found that eating more than 1.3 grams of protein per kilogram of body weight per day helped maintain or even increase muscle mass, while intakes below 1.0 g/kg/day were linked to muscle loss. For a 75 kg person, that means aiming for at least 98 grams of protein daily. Chicken breast, Greek yogurt, eggs, fish, beans, and tofu are all practical ways to hit that number.
Beyond protein, fill the rest of your calories with whatever balance of carbs and fat keeps you satisfied and consistent. Some people find that higher-fat meals keep them full longer. Others do better with more carbs to fuel workouts. Neither approach has a metabolic advantage for fat loss when calories are matched.
Why Your Deficit Shrinks Over Time
One of the most frustrating parts of a calorie deficit is that it becomes less effective the longer you maintain it. This isn’t a willpower problem. It’s a biological response called adaptive thermogenesis. Your body burns fewer calories than expected based on your new, smaller size, essentially working to conserve energy when it senses a sustained shortage.
This metabolic slowdown kicks in fast. Research from the National Institute of Diabetes and Digestive and Kidney Diseases found that after just one week of calorie restriction, participants’ metabolic rates dropped by an average of 178 calories per day more than would be predicted by their weight loss alone. The range was enormous: some people experienced almost no slowdown, while others saw their daily burn drop by nearly 380 calories beyond what was expected. Over six weeks, a 100-calorie-per-day greater-than-predicted drop translated to about 2 kg (4.4 lbs) less weight loss than anticipated.
This is why weight loss stalls are normal and expected. When progress plateaus after several weeks, it usually means your effective deficit has narrowed. You have two options: reduce your calorie intake slightly (by 100 to 200 calories), or increase your activity level. Recalculating your TDEE with your new, lower weight every four to six weeks keeps your deficit from silently disappearing.
Tracking Calories Accurately
A calorie deficit only works if you have a reasonably accurate picture of what you’re eating. Most people underestimate their intake, sometimes substantially. A food scale is the single most useful tool here, especially in the first few weeks while you’re calibrating your sense of portion sizes. Eyeballing a serving of peanut butter or olive oil can easily be off by 100 to 200 calories.
Even with careful tracking, expect some built-in imprecision. The FDA allows calorie counts on packaged food labels to exceed the stated amount by up to 20%. A snack labeled at 200 calories could legally contain 240. This doesn’t mean label-reading is pointless, but it does mean that obsessing over single-digit accuracy isn’t productive. Consistent, approximate tracking beats sporadic perfection.
Apps that use barcode scanning and food databases make daily logging faster, but restaurant meals and homemade recipes with many ingredients are where the biggest errors creep in. When in doubt, slightly overestimate rather than underestimate. If your weight isn’t trending downward after two to three weeks of consistent tracking, your intake estimate is likely too low or your TDEE estimate is too high. Adjust by 100 to 200 calories and observe again.
Putting It All Together
Start by calculating your BMR with the Mifflin-St Jeor equation, multiply by your honest activity level, and subtract 500 calories. Track your food intake with a scale and an app for at least the first month. Weigh yourself at the same time each day (morning, after using the bathroom) and look at the weekly average rather than any single reading, since daily weight can swing by 2 to 4 pounds from water alone.
Keep protein above 1.3 grams per kilogram of body weight to protect muscle. Don’t drop below safe calorie floors. Expect a plateau every few weeks and recalculate your numbers when it happens. The deficit that works is the one you can sustain for months, not the most aggressive one you can white-knuckle through for a week.