Finding your calorie deficit comes down to three steps: estimate how many calories your body burns each day, subtract a specific amount, and then verify it’s working over time. A deficit of 500 calories per day produces roughly one pound of weight loss per week, which the CDC identifies as the sustainable range of 1 to 2 pounds weekly. Here’s how to calculate yours.
Step 1: Estimate Your Resting Metabolic Rate
Your resting metabolic rate (RMR) is the number of calories your body burns just to stay alive: breathing, circulating blood, maintaining body temperature. It accounts for the largest share of your daily calorie burn, so it’s the starting point for every deficit calculation.
The most widely recommended formula is the Mifflin-St Jeor equation, which the Academy of Nutrition and Dietetics considers the most accurate option for estimating RMR. It predicted metabolic rate within 10% of the true measured value in 70% of people studied. The math 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
To convert, divide your weight in pounds by 2.2 for kilograms, and multiply your height in inches by 2.54 for centimeters. For example, a 35-year-old woman who weighs 160 pounds (72.7 kg) and stands 5’6″ (167.6 cm) would calculate: (9.99 × 72.7) + (6.25 × 167.6) − (4.92 × 35) − 161, which comes out to about 1,400 calories per day at rest.
Step 2: Factor In Your Activity Level
Your RMR only covers what your body burns lying in bed all day. To get your total daily energy expenditure (TDEE), the number you actually need for planning a deficit, multiply your RMR by an activity factor:
- Sedentary (desk job, little exercise): multiply by 1.2
- Lightly active (light exercise 1–3 days per week): multiply by 1.375
- Moderately active (moderate exercise 3–5 days per week): multiply by 1.55
- Very active (heavy exercise 6–7 days per week): multiply by 1.725
Using the example above, a lightly active woman with an RMR of 1,400 would multiply by 1.375, giving a TDEE of about 1,925 calories. That’s her estimated maintenance level, the number of calories she’d need to eat each day to stay at the same weight. Most people overestimate their activity category. If you exercise three times a week but sit the rest of the day, “lightly active” is more honest than “moderately active.”
Step 3: Subtract the Right Amount
Harvard Health Publishing recommends eating 500 to 1,000 calories below your maintenance level each day. A 500-calorie daily deficit translates to about one pound of weight loss per week, and a 1,000-calorie deficit targets about two pounds per week. For most people, starting with a 500-calorie deficit is more sustainable and easier to stick with.
The old rule of thumb that 3,500 calories equals one pound of body fat is a useful approximation, but it’s not perfectly linear. Research published in the International Journal of Obesity found that the 3,500-calorie rule roughly holds for people with higher body fat but overestimates the deficit needed for leaner individuals. As you lose weight, a greater proportion of what you lose can come from lean tissue, which is less calorie-dense than fat. This means your results will shift over time, and recalculating every few weeks keeps your numbers closer to reality.
Why Your Deficit Shrinks Over Time
Your body doesn’t passively accept a calorie deficit. All three components of your daily calorie burn decrease as you lose weight. Your resting metabolic rate drops because you’re maintaining less tissue. The energy your body spends digesting food decreases because you’re eating less. And the calories you burn during movement fall because you’re carrying less weight. According to research in The American Journal of Clinical Nutrition, the drop in resting metabolic rate accounts for only about 30 to 50% of the total reduction in calorie burn during weight loss. The rest comes from reduced movement costs and lower digestion energy.
On top of those predictable changes, your body can also reduce calorie burn beyond what the math would predict. Hormones that regulate hunger and metabolism shift: levels of thyroid hormone and the satiety hormone leptin drop, and your nervous system dials back activity in ways that make you unconsciously move less throughout the day. This is why a deficit that produced steady weight loss in month one can stall by month three. The fix is recalculating your TDEE using your current weight every 4 to 6 weeks and adjusting your intake accordingly.
Protect Your Muscle While Losing Fat
A calorie deficit doesn’t only burn fat. Without the right inputs, your body will break down muscle for energy too. The two most effective tools for preventing this are protein intake and resistance training.
Research on athletes and active individuals suggests aiming for 1.6 to 2.4 grams of protein per kilogram of body weight each day during a deficit. For a 160-pound person, that works out to roughly 115 to 175 grams of protein daily. Intakes above 2.4 grams per kilogram don’t appear to provide additional muscle-sparing benefits. Pairing that protein with regular strength training gives your body a strong signal to hold onto muscle and preferentially burn fat.
Account for Tracking Errors
Even careful calorie counting has a built-in margin of error. The FDA allows nutrition labels to be off by as much as 20% from the actual calorie content. A snack labeled at 100 calories could contain 120. Over the course of a full day of eating, those discrepancies can quietly erase a significant chunk of your planned deficit.
This doesn’t mean tracking is pointless. It means you should treat your calorie target as an estimate and use real-world results to calibrate. If you’re eating at what should be a 500-calorie deficit and your weight isn’t budging after two or three weeks, you’re likely eating closer to maintenance than you think. Reducing your target by another 100 to 200 calories, or increasing activity, usually gets things moving again.
Measuring Whether Your Deficit Is Working
The bathroom scale is the most common tracking tool, but it’s also the noisiest. Water retention from sodium, carbohydrate intake, hormonal fluctuations, and even a hard workout can swing your weight by several pounds in a single day. Weigh yourself at the same time each morning and look at the weekly average rather than any single reading.
Body composition matters more than the number on the scale. If you’re strength training while eating in a deficit, you may be losing fat and gaining muscle simultaneously, which can make the scale appear stuck while your body is actually changing. Progress photos taken every two to four weeks, how your clothes fit, and whether your strength in the gym is holding steady or improving are all practical indicators that your deficit is doing what it should. For a more precise picture, methods like a DEXA scan or bioelectrical impedance scales can separately measure fat mass and lean mass, showing you exactly where the changes are happening.
A Practical Example Start to Finish
A 40-year-old man who weighs 200 pounds (90.9 kg), stands 5’10” (177.8 cm), and exercises lightly three days a week would calculate his RMR as: (9.99 × 90.9) + (6.25 × 177.8) − (4.92 × 40) + 5 = roughly 1,825 calories. Multiplied by 1.375 for light activity, his TDEE is about 2,510 calories. Subtracting 500 gives a daily target of around 2,010 calories, which should produce roughly one pound of weight loss per week.
He’d aim for about 145 to 220 grams of protein per day, track his food with the understanding that labels can be off, weigh himself daily but only evaluate the weekly trend, and recalculate every month or so as his weight drops. If progress stalls for more than two weeks, he’d trim another 100 to 200 calories or add a bit more activity rather than making drastic cuts.