Is a 500-calorie deficit the right amount for everyone?

No, it's a commonly used starting point that produces roughly 0.5 kg per week of loss for many people, but the right deficit depends on your TDEE, current weight, and health status. Very large deficits or deficits for people with low body weight can be unsafe, so checking with a doctor before setting an aggressive target is worthwhile.

Why does weight loss slow down even while staying in a deficit?

As you lose weight, your TDEE drops because a lighter body burns fewer calories at rest and during activity. A deficit that was 500 calories at your starting weight becomes a smaller deficit (or no deficit at all) at a lower weight unless calorie intake is recalculated to match the new, lower TDEE.

Does exercise alone create a meaningful calorie deficit without changing diet?

Exercise burns calories, but for most people the calories burned during a typical workout are smaller than expected relative to daily food intake, which is why combining moderate exercise with a modest reduction in calorie intake is generally more sustainable than relying on exercise alone to create a deficit.

How TDEE and Calorie Deficit Actually Work for Weight Loss

Every weight-loss method, whether it's a specific diet, intermittent fasting, or just "eating less," works through the same underlying mechanism: consuming fewer calories than your body burns. TDEE is the number that makes that mechanism concrete, it's an estimate of exactly how many calories your body burns in a typical day, and once you know it, a calorie deficit stops being a vague idea and becomes a specific number of calories to aim for.

What TDEE is actually made of

TDEE isn't one number, it's a sum of several components. The largest is your BMR (Basal Metabolic Rate), the calories your body burns at complete rest just to keep organs functioning, which typically accounts for 60-75% of TDEE. On top of BMR, TDEE adds the thermic effect of food (calories used to digest what you eat, roughly 10%), non-exercise activity like walking and fidgeting, and finally deliberate exercise. The TDEE Calculator estimates the total by taking your BMR and multiplying it by an activity factor, ranging from about 1.2 for a sedentary lifestyle up to 1.9 for very intense physical work or training, since someone who exercises daily burns meaningfully more than their BMR alone would suggest.

Turning TDEE into a deficit that produces real weight loss

Once you have a TDEE estimate, a calorie deficit simply means eating below that number. The commonly cited approximation is that roughly 7,700 calories of deficit corresponds to about 1 kilogram of fat loss (around 3,500 calories per pound), so a consistent daily deficit of 500 calories works out to roughly 0.5 kg lost per week, and a 1,000 calorie deficit to roughly 1 kg per week. These figures are population averages, not exact physics for any one individual, since factors like water retention, muscle changes, and metabolic adaptation all affect the number on the scale week to week. The Calorie Deficit Calculator applies this math directly to a target weekly loss rate.

It's worth noting that very large deficits aren't simply "faster" versions of the same process, cutting calories too aggressively tends to increase muscle loss alongside fat loss and can slow metabolic rate over time, which is why moderate, sustained deficits are generally favored over extreme ones, and why a doctor or dietitian is worth consulting before making major changes to caloric intake.

Why TDEE estimates drift over time

TDEE isn't fixed, it changes as your weight, activity level, and body composition change, which is why the same calorie target that produced weight loss a few months ago can stop working: as body weight drops, BMR (and therefore TDEE) drops with it, since a smaller body requires fewer calories to maintain. Recalculating TDEE periodically, and pairing it with a broader look at macros rather than calories alone, keeps the target aligned with where your body actually is rather than where it started.