Calorie Deficit: How to Calculate and Use It for Weight Loss
A calorie deficit means eating fewer calories than you burn, so your body draws on stored energy, mostly fat. To size one you need an estimate of your total daily energy expenditure (TDEE); this page shows how to get it, how big a deficit to aim for, and how to adjust as you go.
What Is a Calorie Deficit and Why Does It Matter?
When food doesn't supply the energy your body needs, it draws on stored energy. A common rule of thumb is that a pound of body fat stores about 3,500 calories, so a 3,500-calorie deficit is often equated with a pound lost. It's a useful starting estimate, but real-world loss slows over time as your body adapts and your weight falls, which is why the NIH Body Weight Planner models the slowdown instead of assuming a fixed rate.
You can create the deficit by eating less, moving more, or both. The 2013 American Heart Association/American College of Cardiology/The Obesity Society guideline lists a deficit of 500 or 750 calories a day as one option, which by the 3,500-calorie rule works out to roughly 1 to 1.5 pounds a week at first. The CDC describes 1 to 2 pounds a week, from eating 500 to 1,000 fewer calories a day, as a gradual pace that people are more likely to maintain.
Bigger isn't better: very large deficits make it harder to get enough protein and nutrients, increase muscle loss, and are hard to sustain.
Understanding Your Total Daily Energy Expenditure (TDEE)
Your TDEE has four parts:
Basal metabolic rate (BMR), the energy for breathing, circulation and organ function at rest, is usually the largest share, often around 60–70% for people who aren't very active. It is estimated from age, sex, height and weight and then multiplied by an activity factor.
Thermic effect of food (TEF) is the energy used to digest and process food, roughly 10% of intake. Protein costs the most to process.
Exercise activity thermogenesis (EAT) covers planned exercise and varies widely from person to person and day to day.
Non-exercise activity thermogenesis (NEAT) is all other movement: walking around, standing, fidgeting, chores. It can differ by hundreds of calories a day between people with similar builds.
Example: a 35-year-old woman who weighs 150 pounds (68 kg), is 5'6" (168 cm) and is moderately active. Mifflin-St Jeor BMR = 10 × 68 + 6.25 × 168 − 5 × 35 − 161 = 680 + 1,050 − 175 − 161 = 1,394 calories. TDEE = 1,394 × 1.55 ≈ 2,161 calories a day. The Resting Metabolic Rate calculator runs this equation (leave body fat blank), and you apply the activity multiplier; the TDEE calculator does the same with the revised Harris-Benedict equation, which usually lands a few percent higher.
How to Calculate Your Calorie Deficit
Step 1: Estimate your TDEE. Use one of the calculators above. Pick the activity level that matches what you actually do; overstating it is the most common error.
Step 2: Set a realistic pace. A loss of about 1 to 2 pounds a week corresponds to a daily deficit of about 500 to 1,000 calories by the 3,500-calorie rule. For reference, the 2013 AHA/ACC/TOS guideline's typical intake targets for weight loss are 1,200 to 1,500 calories a day for women and 1,500 to 1,800 for men; going lower is best done with medical supervision.
Step 3: Calculate your target intake. Subtract the deficit from your TDEE. In the example: 2,161 (TDEE) − 500 (deficit) = 1,661 calories a day, for roughly a pound a week at first. The Calorie Deficit calculator does this from your TDEE, current and target weight and timeframe, caps the deficit at the pace you choose (0.25, 0.5 or 0.75 kg a week) and never returns a target below 1,200 calories. The Calorie Deficit & Weight Loss calculator works the other way: enter your maintenance calories, a target intake, any extra exercise calories and a number of weeks, and it estimates the weight you would lose.
Step 4: Monitor and adjust. Track your progress for 2–3 weeks. If you're losing more than 2 pounds a week, add calories. If progress stalls, recheck your intake records and activity level.
As you lose weight your TDEE falls, so recalculate the deficit periodically.
Creating the Deficit: Diet vs. Exercise
Diet changes create a deficit most efficiently: skipping a 300-calorie snack is easier than burning 300 calories. Vegetables, lean proteins and whole grains give more food for fewer calories.
Exercise brings benefits beyond calories, including cardiovascular fitness, mood, and help keeping muscle while losing weight; strength training is particularly useful for the last.
Combining both spreads the effort: eating 300 calories less and burning 300 more gives a 600-calorie deficit without severe restriction.
Example: John weighs 200 pounds with a TDEE of 2,800 calories. To lose about 1.5 pounds a week he needs a 750-calorie deficit. He could:
- Eat 2,050 calories (750-calorie reduction)
- Eat 2,425 calories and burn 375 through exercise
- Eat 2,500 calories and burn 450 through exercise
Common Mistakes and How to Avoid Them
Overestimating exercise calories. Calorie figures from fitness trackers and gym machines can be well off. Treat them as rough and don't eat all of them back.
Underestimating food intake. Self-reported intake is commonly lower than actual intake. Food scales, measuring cups and a tracking app help.
Creating excessive deficits. Very low-calorie diets are hard to sustain and make it harder to keep muscle. Moderate deficits are easier to stick with.
Ignoring body composition. The scale doesn't distinguish between fat and muscle loss. Monitor body measurements and how clothes fit, not just weight. A BMI calculator adds context for your progress.
Expecting linear progress. Water retention, hormonal fluctuations and muscle gain all move the scale. Focus on trends over 2–4 weeks rather than daily readings.
Not adjusting over time. As you lose weight, your calorie needs fall. Recalculate your TDEE every 10 to 15 pounds lost to keep the deficit.
These figures are estimates for healthy adults, not medical advice. If you are pregnant, breastfeeding, under 18, or have a medical condition or a history of disordered eating, get targets from a clinician or dietitian.