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Calorie Deficit Calculator

Find your target calories and weeks to goal weight at a chosen deficit size.

Written by Golam Rabbani, Founder & Lead Engineer — Last updated 2026-05-01

Use a TDEE calculator if unsure.

How to use this calorie deficit calculator

  1. Toggle kg or lbs at the top of the form.
  2. Enter your current weight and your goal weight (goal must be lower).
  3. Enter your TDEE (use a TDEE calculator first if you don't know it).
  4. Pick a deficit size: Mild −250, Moderate −500, or Aggressive −750 kcal/day.
  5. Press Calculate to see your target intake, total kcal to burn, weeks needed, and estimated end date.

About this calorie deficit calculator

The calorie deficit calculator works out the daily calorie target needed to lose a specific amount of weight at the deficit size you choose, plus how long the cut should take. It assumes 1 kg of body fat stores roughly 7,700 kcal, so total kcal to lose = weight to lose × 7,700, and weeks needed = total kcal ÷ (deficit × 7).

The 7,700 kcal/kg figure derives from the classic Wishnofsky rule of "3,500 kcal per pound" of fat (Wishnofsky M. Am J Clin Nutr 1958;6(5):542-6). Modern research shows real-world rates often run a bit slower because metabolism adapts during a deficit, so treat the weeks estimate as an upper-bound speed. This is an estimate for informational purposes and is not a substitute for advice from a registered dietitian or qualified clinician — very-low-calorie diets warrant medical supervision.

For example, an 85 kg person aiming for 75 kg, with a TDEE of 2,500 kcal/day and a Moderate (−500) deficit: target intake = 2,000 kcal/day; weight to lose = 10 kg; total kcal to burn = 10 × 7,700 = 77,000 kcal; weeks = 77,000 ÷ (500 × 7) ≈ 22 weeks. The tool is useful for setting a realistic timeline before starting a cut and for comparing how Mild vs Aggressive deficits change the finish date.

FAQ

What's the safest deficit size?
Mild (−250) and Moderate (−500) deficits are sustainable for most people. Aggressive (−750) is best reserved for shorter cuts or for people with higher body-fat reserves and is harder to maintain energy and training quality on.
Where does the 7,700 kcal per kg number come from?
It originates with Wishnofsky's 1958 estimate that 1 lb (≈ 0.454 kg) of body fat stores 3,500 kcal — equivalent to 7,700 kcal/kg. It is a useful planning shortcut, not a precise rate; real loss includes water and a small amount of lean tissue.
Why does my weekly weight loss slow down over time?
As you lose weight, your TDEE also falls because you have less mass to move and a slightly lower BMR. Re-run the calculator with your updated weight and TDEE every 4–6 weeks.
How low can my target intake go?
Most guidelines suggest staying above 1,200 kcal/day for women and 1,500 for men outside medical supervision. If the tool's target falls below that, pick a smaller deficit or raise your TDEE by adding activity.
Does this tool save my data?
No. Weight, TDEE, and goal stay in your browser and are cleared when you close the tab.
Is the calorie deficit calculator free?
Yes — completely free, no signup or limits.