About the Calorie Deficit Calculator
A calorie deficit means eating fewer calories than your body burns, and it is how fat loss happens. This calculator turns the idea into a timetable. Give it your current weight, the weight you want to reach and the size of your daily deficit, and it works out the total calories to cut, how many days that takes, the loss you can expect each week and, with a start date, the day you would arrive. It uses the standard rule of thumb of about 7,700 kilocalories per kilogram, or 3,500 per pound, so the answer is a guide, not a promise.
Updated October 2026
How to use the Calorie Deficit Calculator
- 1Choose kilograms or pounds.
- 2Enter your current weight and your goal weight.
- 3Enter the calories per day you plan to cut. A 500 kcal deficit is a common starting point.
- 4Optional: pick a start date to see the date you could reach your goal.
- 5Check the pace note, and adjust the deficit if the weekly loss looks too fast.
How the maths works
The calculator multiplies the weight you want to lose by 7,700 kcal per kilogram, then divides by your daily deficit and rounds up to whole days. Losing 8 kg at 500 kcal a day needs 61,600 kcal, which is 124 days.
Weekly loss is your deficit times seven, divided by the same energy figure. A 500 kcal deficit works out to about 0.45 kg a week.
Making the plan realistic
- Set goals in steps of 3 to 5 kg and recalculate after each one.
- Plan for plateaus and holidays by adding a few weeks.
- Keep protein high and train with weights to hold on to muscle.
- Weigh yourself under the same conditions each time, such as in the morning after using the toilet.
Going further
A deficit is only half the story, because what you eat also affects hunger, energy and health. Use the Macro Calculator to split your calories into protein, carbohydrate and fat, and the Weight Loss Percentage Calculator to track how far you have come. The Ideal Weight Calculator can help you choose a sensible goal.
Features
- Days, weeks and months to your goal
- Weekly loss in your chosen unit
- Optional finish date from a start date
- Warning when the pace is aggressive
- Kilograms and pounds supported
- Private: nothing is saved or sent
Frequently asked questions
How many calories make a kilogram of fat?
The usual estimate is about 7,700 kilocalories per kilogram of body fat, or 3,500 per pound. It is an average from the energy content of fat tissue. In real life the water, muscle and gut contents also change, so the scale does not follow it perfectly.
How big should my calorie deficit be?
Most guidance suggests 300 to 750 kcal a day, which gives roughly 0.25 to 0.75 kg a week. Bigger deficits are harder to keep up, can lead to muscle loss and tiredness, and should only be used under medical supervision.
Why am I losing weight slower than the calculator says?
Your body burns fewer calories as you lose weight, and many people eat or move a little differently over time. Water retention, hormones and measuring errors in food logs add noise. Look at the trend over several weeks rather than single days.
How do I know my daily calorie burn?
Your total daily energy expenditure depends on your size, age, sex and activity. The TDEE Calculator and BMR Calculator on this site estimate it. Subtract your deficit from that number to get a daily calorie target.
Is it safe to lose weight quickly?
Losing more than about 1 percent of your body weight a week is hard to sustain and can bring gallstones, muscle loss and low energy. Anyone with a medical condition, who is pregnant or who is under 18 should ask a professional first.
Can I create the deficit with exercise instead of food?
You can use both. Exercise burns calories and helps keep muscle, but food is the easier lever, since a 500 kcal deficit is about one hour of brisk running. Most people reach the deficit with a mix of eating a little less and moving more.