Calorie Intake Calculator

Calorie deficit, explained

Every weight-loss diet works through a calorie deficit. Understanding it makes plateaus far less confusing.

Updated 22 October 2026 · 6 min read

What a deficit does

When you take in less energy than you use, your body makes up the difference from its stores, mainly fat and some glycogen and protein. Over weeks, that shows up as weight loss. It does not matter which diet creates the deficit: low-fat, low-carb, intermittent fasting or simply smaller portions all work through the same mechanism.

The 7,700 kcal (3,500 kcal) rule

A kilogram of body fat tissue stores roughly 7,700 kcal, or about 3,500 kcal per pound. So a 500 kcal daily deficit should mean about 0.5 kg (1 lb) a week. It is a good rule for planning the first few months, but it overestimates long-term loss because:

  • Your BMR falls as you get lighter.
  • You tend to move a little less without noticing.
  • Early loss includes water, which makes the first week look better than later weeks.

Choosing a size

Use 10 to 25% below your TDEE, or 0.5 to 1% of your body weight lost per week. Smaller deficits make sense close to your goal and when you want to build strength at the same time. Use the calorie deficit calculator to turn a goal date into a daily number.

Plateaus

A week without change is normal. Water retention from salt, stress, travel, hard training or the menstrual cycle can hide fat loss for a week or two. A true plateau is three or more weeks of flat weekly averages. If that happens:

  1. Check portions and drinks honestly for a week.
  2. Recalculate with your new weight.
  3. Add 2,000–3,000 daily steps before cutting food further.
  4. Consider a week or two at maintenance to reset hunger and energy.

Protecting muscle

Strength training two or three times a week and eating enough protein, around 1.8 g per kg of body weight, help make sure the weight you lose is mostly fat. That keeps your metabolism higher and makes maintenance easier afterwards.

Frequently asked questions

Can you lose fat without a deficit?
Body recomposition, losing fat while gaining muscle at about the same weight, is possible for beginners and people returning to training. For overall fat loss, a deficit is required.
Does intermittent fasting burn more fat?
Studies find it works about as well as daily calorie reduction when total calories are matched. It is a useful tool if it makes a deficit easier for you.

This guide is general information, not medical advice. See our disclaimer and how we calculate.