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Calorie Deficit

By Pilar Gutiérrez-Larsson, RD, CDN, MA, BS · Updated

Calorie Deficit. A calorie deficit means you're eating fewer calories than your body burns each day. It's the basic mechanism behind most weight loss: when you take in less energy than you use, your body taps stored fat to make up the difference, and over time that adds up to weight loss.

What is a calorie deficit, in plain language?

A calorie deficit is when you eat less energy than you burn. If your body uses 2,000 calories on a typical day and you eat 1,700, you’re in a 300-calorie deficit. Over time, deficits like this typically lead to weight loss because your body has to use stored energy (mostly body fat) to cover the gap.

The arithmetic is simple. The biology is approximately simple but with some asterisks. The behavioral part — actually maintaining the deficit consistently — is where everything gets harder.

How big should a deficit be?

For sustainable weight loss in adults, a deficit of 200 to 500 calories per day is the friendliest range. That works out to about 0.4 to 1 pound per week of weight loss, depending on body size and individual physiology.

Bigger deficits (700-1,000 calories/day) can produce faster weight loss in the short term, but they’re harder to sustain. The dropout rate goes up, the hunger gets harder, and most people end up eating back the deficit on weekends. A small, sustainable deficit usually wins over a big, sporadic one.

How do I know my deficit?

You need to know two things:

  1. How many calories you eat. A calorie tracker app gives you this, give or take the app’s accuracy.
  2. How many calories you burn. This is harder to know precisely. Apps estimate it from your age, sex, height, weight, and activity level. The estimate is usually within 10-15% of true.

Subtract one from the other. The difference is your deficit (or surplus, if you ate more than you burned).

For most people, the practical answer is: eat 300-500 calories less per day than the app’s calculated maintenance number, give it 4-6 weeks, and adjust based on actual weight change. If you’re losing weight at the rate you wanted, the deficit was about right. If you’re not losing weight, your maintenance estimate was probably too high — eat 200 calories less and try again.

What about exercise?

Exercise burns calories, which can contribute to a deficit. But for most beginners, the math of “eat less” is more powerful than “exercise more.” A typical 30-minute jog burns around 250-300 calories. A typical handful of nuts contains 200 calories. Skipping the nuts is roughly equivalent to the jog, with fewer logistics.

Exercise has many other benefits — cardiovascular health, mood, sleep, muscle preservation — and most weight-loss programs work better with some exercise included. But the “exercise off” approach to weight loss alone is harder than the “eat less” approach.

Common deficit pitfalls

A few things that derail beginners’ deficits:

Calorie deficits aren’t for everyone

If you have a history of disordered eating, a deficit-based approach is not the right tool. Talk to a Registered Dietitian or therapist before considering any structured calorie reduction. The NEDA helpline is 1-800-931-2237.

Also: children, teenagers, pregnant or postpartum people, and adults under specific medical care should not casually pursue calorie deficits. The right tool in those cases is professional guidance.

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