What Is a Calorie Deficit?

A calorie deficit is when you eat fewer calories than your body burns in a day: your TDEE, or Total Daily Energy Expenditure. To make up the missing energy, your body draws on stored fat, which leads to weight loss over time. This is the only scientifically proven principle behind weight loss; no diet, regardless of what it restricts or emphasizes, can bypass this energy-balance rule.

How to Calculate a Calorie Deficit

To calculate a calorie deficit, you first need to know your daily calorie needs (TDEE). TDEE is calculated using the Mifflin-St Jeor formula based on your age, sex, height, weight, and activity level. Once you know your TDEE, you subtract your desired deficit from it:

Target Calories = TDEE − Desired Deficit

For example, if your TDEE is 2,200 calories and you're targeting a 500-calorie deficit, you'd aim for 1,700 calories a day. Instead of calculating your TDEE by hand, you can get it in seconds with our free calorie calculator.

How Big Should a Calorie Deficit Be?

The generally accepted approach is a deficit of 10-20% below your TDEE, which usually works out to about 300-750 calories a day and supports healthy weight loss of roughly 0.5-1 kg (1-2 lb) per week. Very large deficits (1,000+ calories a day) can produce fast short-term results, but they also tend to cause muscle loss, low energy, and metabolic slowdown, making them hard to sustain.

I'm in a Calorie Deficit but Not Losing Weight, Why?

This is one of the most common frustrations. If the scale isn't moving despite what you believe is a deficit, one or more of these factors is usually at play:

  • An inaccurate TDEE: Overestimating your activity level can mean you're actually at maintenance, not in a deficit.
  • Uncounted calories: Sauces, snacks, sugary drinks, and "just a bite" tastes can add up to a significant chunk of your daily intake.
  • Water retention: Sodium intake, hormonal cycles, stress, and intense training can cause short-term water retention that masks fat loss on the scale.
  • Poor sleep and stress: Chronic sleep deprivation and high stress raise cortisol, which can increase water retention and appetite.
  • Metabolic adaptation: Prolonged calorie restriction can somewhat slow your energy expenditure over time, so it helps to recalculate your target calories as you lose weight.

Day-to-day scale fluctuations are normal. Looking at your weekly average, rather than any single reading, is a far more reliable way to track progress.

Practical Tips

  • Track your calorie intake consistently for at least a few weeks; a single day's measurement isn't enough to draw conclusions from.
  • Keep protein intake high; it supports fullness and helps prevent muscle loss. Use our macro calculator to find the right protein/carb/fat split for your goal.
  • Recalculate your TDEE every 4-6 weeks based on your current weight.
  • Judge progress by your weekly average weight, not daily readings.