Calorie Deficit Calculator
Pick a rate of loss and this works out the daily intake that produces it, along with how long reaching your goal weight would take at that pace.
Fill in the fields above to see your result.
How the arithmetic works
A pound of body fat stores roughly 3,500 calories. Run a deficit of 500 calories a day and that is 3,500 across a week, or about one pound. Double the deficit and you roughly double the rate.
That is the theory, and it is a useful approximation. It is also an oversimplification, because the 3,500 figure assumes all lost weight is fat and that your expenditure stays constant while you shrink. Neither holds.
Why real loss is slower than the arithmetic predicts
As you lose weight your body needs fewer calories to run, so the deficit you started with narrows on its own. A 500 calorie gap at 220 pounds is a smaller gap at 190 pounds without you changing anything.
Unconscious movement also falls during a deficit. You fidget less, stand less, and move less between deliberate activities. This is not laziness, it is regulation, and it can account for a few hundred calories a day.
Some of what you lose is also lean tissue and water rather than fat, particularly early on and particularly if protein intake is low. This is why the first week often shows a dramatic drop that then stalls.
Choosing a rate you can actually hold
The right rate is the fastest one you can sustain without your life falling apart, which for most people is between half a pound and one pound a week. Aggressive deficits work on a spreadsheet and fail in practice, because hunger, fatigue, and social friction compound.
A slower plan you follow for a year beats an aggressive plan you abandon in six weeks. This is the single most common mistake we see in intake forms.
The floor this calculator will not go below
We clamp the result at 1,200 calories for women and 1,500 for men. Below those levels it becomes genuinely difficult to meet protein and micronutrient needs, and muscle loss accelerates.
Very low calorie diets do exist in clinical practice, but they are run under medical supervision with monitoring and supplementation. They are not something to improvise from a web calculator.
Where medication fits
A GLP-1 does not change the arithmetic. It changes how difficult the arithmetic is to follow, by reducing appetite so that a deficit stops feeling like constant restraint.
That is the honest description of what the medication does. It makes an achievable plan bearable. It does not replace the plan.
Common questions
A calculator cannot read your blood work
These numbers are estimates from formulas. A clinician works from your actual labs, history, and how your body responds month to month.
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