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Calorie Deficit and Weight Loss Timeline

How long a given deficit actually takes.

Inputs
kcal

From a TDEE or BMR estimate, or your own tracked average.

kg
500kcal
Time to goal
17.6 weeks
SlowSustainableAggressiveToo steep
Daily intake
1900 kcal
Loss per week
0.45 kg
Deficit as a share of maintenance
20.83%
About
4.05 months
weeks = (kg to lose × 7700) ÷ (daily deficit × 7)

The 7,700 kcal per kg figure is an approximation. Real loss slows as you get lighter, because a smaller body burns less — expect the last stretch to take longer than this suggests.

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A kilogram of body fat holds roughly 7,700 calories. A 500 kcal daily deficit is 3,500 a week, so about 0.45 kg — meaning 8 kg takes around 17 weeks, slowing slightly as you get lighter.

How to use Calorie Deficit Calculator

  1. Enter your maintenance calories. From a BMR estimate with an activity multiplier, or your own tracked average.
  2. Enter the weight to lose. And choose a daily deficit.
  3. Check the share of maintenance. A deficit past about 30% of maintenance is where problems start.

About calculating a calorie deficit

Weight loss arithmetic rests on one number: a kilogram of body fat stores approximately 7,700 calories, the metric form of the familiar 3,500 per pound. Divide the deficit into the target and you have a timeline. The number is a reasonable approximation and it flatters the later stages. It assumes the deficit stays constant, but maintenance is a function of bodyweight, so as you get lighter the same intake represents a smaller deficit and the rate slows. A plan built on the linear figure will run ahead of reality by the end, which is a common and demoralising surprise for anyone who did the maths at the start and expected it to hold. Deficit size is the decision that matters most, and it is best judged as a percentage of maintenance rather than as an absolute number — 500 calories is a moderate deficit for a large active person and a severe one for a small sedentary one. Around 20 to 25% is the range most often recommended, because larger deficits take a greater share of the loss from muscle rather than fat, become progressively harder to hold, and have a poor record of ending well. The scale is also worth reading in the other direction. Below roughly 1,200 to 1,500 calories, depending on size and sex, meeting nutritional needs from food becomes genuinely difficult. When the target requires going there, the productive change is to raise maintenance through activity rather than cut intake further.

Frequently asked questions

Is 3,500 calories per pound accurate?
It is a useful approximation and it overstates long-term loss. The figure assumes the deficit stays constant, but maintenance falls as bodyweight falls, so the same intake becomes a smaller deficit over time. Expect the later weeks to be slower than the arithmetic suggests.
How large should a deficit be?
Around 20 to 25% of maintenance is the usual recommendation. Larger deficits lose weight faster and lose more of it as muscle, are harder to sustain, and tend to end in the rebound that makes the average worse than a slower approach would have been.
Why has my weight stopped falling?
Most commonly because maintenance has fallen with bodyweight and the deficit has closed. Water retention also masks fat loss for weeks at a time, particularly around changes in training or carbohydrate intake. Judge by a multi-week trend, not by single readings.
What is the lowest intake that is safe?
Below roughly 1,200 calories for women and 1,500 for men it becomes difficult to meet protein, vitamin and mineral needs from food. If the arithmetic pushes you under that, the answer is to raise maintenance through activity rather than to cut further.
Does protein matter during a deficit?
Considerably. Higher protein preserves lean mass while calories are restricted and is the most satiating of the three macronutrients, which makes the deficit easier to hold. It is the single most useful dietary adjustment during weight loss.

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