Calorie Deficit Calculator
Calorie deficit calculator to lose weight: compare a daily intake with your maintenance calories, see the real deficit after the safety floor, and weekly loss.
Results
How to calculate a calorie deficit
A deficit is maintenance minus intake, so calculating a calorie deficit means establishing maintenance first. This free calorie deficit calculator estimates maintenance from your height, weight, age, sex and activity level, compares it against the daily intake target you enter, and reports the difference along with the weekly weight change it implies.
Both halves are shown rather than just the answer. Knowing how to calculate calorie deficit figures by hand is the same two steps: get a maintenance estimate, then subtract. The page exists to make the first step defensible, not to hide it.
To calculate calories deficit in the other direction, start from a rate. The conventional energy density of body mass is 7,700 kcal per kilogram, so a 0.5 kg weekly target implies roughly 550 kcal a day.
The calorie deficit formula
Written out: deficit = maintenance calories - intake calories, and weekly change = (deficit x 7) / 7,700 in kilograms. Working out how to calculate deficit calories from a goal simply runs that second equation backwards.
Worked through: maintenance of 2,400 kcal against an intake of 1,900 is a 500 kcal deficit, which across a week is 3,500 kcal, which divided by 7,700 is about 0.45 kg. The constant assumes every kilogram carries the same energy and that the deficit keeps working at full strength, and neither is exactly true.
How this calorie-deficit estimate works
The route estimates maintenance calories first, then compares that maintenance figure with the intake target you enter. If your entered target falls below the published minimum for your sex, the delivered intake is raised and the calculator reports the smaller deficit you would actually be following.
The floor is 1,500 kcal a day for men and 1,200 for women, and the result says which of three things happened:
| Floor status | What it means |
|---|---|
| Not applied | Your target already clears the floor, so the deficit you asked for is served |
| Raised to floor | Your target fell below the floor, so intake is raised and the deficit shrinks |
| Maintenance below floor | Maintenance is already at or under the floor, so no deficit is safe |
Why the delivered deficit can differ from the one you asked for
A calorie target below the published minimum is not left on screen as a warning. The target itself is adjusted, because a warning that left the unsafe number in place would not be a real safeguard.
Sources and limitations
Sources reviewed 27 August 2026. This is an educational estimate for healthy adults and not medical or dietary advice.
It is not suitable during pregnancy or breastfeeding, for children or adolescents, or for anyone managing an eating disorder or a condition that affects weight or metabolism. If you want a timeline to a target weight rather than a deficit figure, the weight loss calculator takes the same inputs and reports that instead.
Frequently asked questions
Why can the delivered deficit be smaller than the target I typed?
Because the calculator preserves the published minimum intake floor. If your entered target falls below it, the delivered intake is raised and the reported deficit becomes smaller. It shows how to calculate a calorie deficit: the daily calories for your goal and the deficit they represent below your maintenance calories.
How do I calculate a calorie deficit?
Subtract your intake from your maintenance calories. Calculating a calorie deficit therefore needs a maintenance figure first, which comes from a resting metabolic rate and an activity factor. This page works that out and then does the subtraction, showing both halves so the arithmetic is checkable.
What is the calorie deficit formula?
Deficit equals maintenance minus intake. To turn a deficit into weight, the conventional energy density of body mass is 7,700 kcal per kilogram, or roughly 3,500 per pound. A 500 kcal daily deficit is 3,500 a week, which is about 0.45 kg. That constant is an approximation, not a law.
Do I need a calorie counter to use this?
Not to get the target. A calorie counter tracks what you actually eat; this page tells you the number worth tracking against. Work the deficit out here, then use whichever food diary you prefer to check your intake against it.
Why can the deficit be smaller than the one I entered?
Because no intake target is reported below the published minimum of 1,500 kcal a day for men or 1,200 for women. If your entered target falls under it, intake is raised to the floor and the reported deficit shrinks accordingly. Where maintenance is already at or below the floor, no deficit can be served safely at all.
How many calories to lose weight, and how big should the deficit be?
This page does not prescribe one. Conventional starting points sit between 250 and 500 kcal a day, and larger deficits make the floor more likely to bind. The calculator reports what your entered target actually delivers rather than recommending a figure.
How many calories should I cut to lose weight?
Between 300 and 500 a day below maintenance for most people. That is how many calories to lose weight at a steady 0.25 to 0.5 kg a week without losing much muscle or running into the intake floor. A larger cut works faster on paper but is harder to hold and often collides with the 1,200 or 1,500 calorie minimum, at which point the deficit this calculator can deliver is smaller than the one you asked for. Add activity rather than cutting further if you hit that floor.