Calorie Deficit Calculator
Work out the daily deficit a goal weight actually needs, and whether that goal is a sensible one.
A calorie deficit is the gap between the calories you burn and the calories you eat. A kilogram of body weight is commonly estimated at about 7,700 calories, or 3,500 per pound, so losing 0.5 kg a week needs roughly a 550 calorie daily deficit, though on a smaller daily burn that is more than a quarter of what you use, which is where this tool starts warning you. The 7,700 figure is an approximation that overstates loss over long periods, because metabolism adapts as weight falls.
This calculator is for general education only and is not medical advice, diagnosis, or treatment, and it is not a weight loss program. Energy needs vary between individuals by roughly 20%, and the conversion it uses is an approximation that overstates loss over long timeframes. Do not use it to plan an aggressive deficit. If you are under 18, pregnant or breastfeeding, managing a health condition, or have any history of disordered eating, please speak to a doctor or a registered dietitian instead of using a calculator. In the US, the National Alliance for Eating Disorders runs a free helpline staffed by licensed eating-disorder therapists on 1-866-662-1235, Monday to Friday, 9am to 7pm ET. In a crisis at any hour, call or text 988.
Daily deficit you need
Eat this much below your daily burn to move toward your goal weight.
- Target intake
- 1,888 kcal a day
- Weekly rate of loss
- 0.63 lb (0.28 kg) a week
- Time you gave it
- 168 days
- Total energy gap to the goal
- 52,390 kcal
- BMI at your goal weight
- 24.4
Your daily burn minus that deficit.
The timeframe you entered, in whole days.
At about 7,700 kcal per kg of body weight.
The goal check looks at this figure, and flags anything under 18.5.
Each figure is rounded once, where it is displayed, so the arithmetic can land a calorie either side if you redo it yourself. These are estimates for adults and the conversion behind them is an approximation. See the notes below.
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About the Calorie Deficit Calculator
This calculator works backwards from a goal, in either direction: enter a goal weight above your current one and it works out the surplus instead of the deficit. You give it your current weight, the weight you want to reach, and how long you want to take. It works out the total energy gap that implies, divides it across your timeframe, and subtracts it from the calories you burn in a day to give a target intake. The conversion it uses is the Wishnofsky rule from 1958: roughly 7,700 calories per kilogram of body weight, or 3,500 per pound. That rule is the industry standard and it is also a simplification. It assumes a straight line, and real weight loss is not one. As you get lighter you burn less, and your body adapts to sustained restriction, so a projection that looks right at three months will overstate what actually happens at two years. The tool flags long timeframes for exactly that reason. It also checks the things a bare arithmetic answer would skip. It checks the pace, against a ceiling of about 1% of body weight or 0.9 kg per week, whichever is lower. It checks the size of the deficit, against 1,000 calories a day or 25% of your daily burn, whichever is smaller. It checks the resulting intake against commonly cited minimums. And it checks the goal weight itself, because a gentle, patient, perfectly paced plan toward a weight that is too low is still a plan toward a weight that is too low, and a calculator that stays silent about that is not neutral, it is endorsing.
Frequently asked questions
How big should a calorie deficit be?+
How big a deficit is safe depends on how much you burn, not on a fixed number. This tool flags any deficit at or above 1,000 calories a day, or a quarter of your daily burn, whichever is smaller. For most people that lands between 300 and 500 calories a day, or roughly 0.27 to 0.45 kg a week. The pace ceiling works the same way: about 1% of your body weight per week, up to a limit of 0.9 kg. Below about 90 kg that means a heavier person can lose faster in absolute terms, and above it the flat 0.9 kg cap takes over.
Why does this calculator ask for my height?+
So it can check whether your goal weight is a reasonable place to be aiming. Weight on its own says very little without height. If the goal you enter falls below the WHO underweight threshold of a BMI of 18.5, the tool leads with a caution about the destination before it shows you the figures, and below a BMI of 17 it shows no figures at all.
Is the 3,500 calories per pound rule accurate?+
It is a reasonable approximation over weeks and a poor one over years. It assumes your energy burn stays constant while you lose weight, and it does not: a lighter body burns less, and prolonged restriction lowers expenditure further. Over a few months the error is modest. Over two years or more the linear projection can be out by a wide margin, always in the optimistic direction.
What is the lowest number of calories I should eat?+
The commonly cited screening minimums are about 1,200 a day for women and 1,500 for men, and this tool warns you when a plan falls below them. Those are general figures, not personal advice. Very low calorie diets do exist as a clinical intervention, and they belong under medical supervision, not a web calculator.
Why is my weight not falling the way the plan says?+
Day to day weight moves with water, food in transit, salt, sleep and hormones, and those swings are often larger than a week of fat loss. Look at a two to three week trend rather than single readings. If the trend is genuinely flat for a month, the likeliest explanation is that your actual intake or your estimated burn differs from the numbers, not that the arithmetic is wrong.
What if the tool will not show me a plan?+
If the goal weight you enter falls below the WHO underweight threshold of a BMI of 18.5, the tool leads with a caution about the destination before it shows you anything else, and the figures appear underneath it. Below a BMI of 17 it shows no figures at all. That is deliberate, and it is not a judgment about you. A goal that low is worth talking through with a doctor or a dietitian before you start.
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