Find the daily calorie deficit you need to reach your goal weight by a target date, plus the target calorie intake for your activity level. The calculator uses the Mifflin-St Jeor equation for your BMR and the standard estimate that 1 kg of body fat holds about 7,700 kcal.
The calorie deficit calculator works out exactly how much you need to cut your daily calories to reach a target weight by a date you choose. A calorie deficit — eating fewer calories than your body burns — is the fundamental driver of weight loss, and this tool turns your goal into a concrete daily number. Enter your sex, age, height, current weight, target weight, and target date, and the calculator returns the daily deficit required, the target calorie intake for every activity level, and how fast you will be losing weight. It uses the trusted Mifflin-St Jeor equation for your metabolic rate and the widely used figure that a kilogram of body fat stores roughly 7,700 calories.
This page explains what a calorie deficit is, the science that connects calories to weight change, the exact formulas the calculator uses, worked examples, how to diet safely, and answers to the questions people ask most. By the end you will understand not just the number, but how to reach your goal in a healthy, sustainable way.
A calorie deficit is simply the state of consuming fewer calories than you expend. Your body needs energy every day to keep you alive and moving — to breathe, pump blood, digest food, think, and perform every activity from typing to sprinting. That total daily energy requirement is called your total daily energy expenditure, or TDEE. When the calories you eat (calories in) fall below the calories you burn (calories out), your body makes up the difference by tapping into stored energy, mostly body fat, and you lose weight. Put simply: calorie deficit = calories in − calories out, and when that number is negative, you are in a deficit and heading toward weight loss.
The link between calories and body weight rests on a well-established estimate: one kilogram of body fat stores about 7,700 calories (roughly 3,500 calories per pound). This means that to lose one kilogram of fat, you need a cumulative deficit of about 7,700 calories over time. It is the reason a daily deficit of about 500 calories leads to roughly half a kilogram (about one pound) of fat loss per week: 500 × 7 = 3,500 calories, which is close to one pound of fat. The calculator uses this relationship in reverse — it takes the total weight you want to lose, multiplies by 7,700 to get the total calorie gap, and divides by the number of days until your target date to give the daily deficit you need.
The calculator combines three well-known relationships. First, it estimates your basal metabolic rate (BMR) — the calories you burn at complete rest — using the Mifflin-St Jeor equation:
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
Second, it multiplies your BMR by a physical activity factor to get your TDEE (maintenance calories):
TDEE = BMR × activity factor
Third, it converts your weight goal and time frame into a daily deficit:
Daily deficit = (current weight − target weight) in kg × 7,700 ÷ days until target
Your target calorie intake for a given activity level is then simply your TDEE at that level minus the daily deficit. Because the right number depends on how active you are, the calculator shows the target intake for all five activity levels so you can pick the one that matches your lifestyle.
Your activity factor scales your resting metabolism up to your real daily burn. The five standard levels are:
| Activity level | Factor |
|---|---|
| Sedentary — little or no exercise | 1.2 |
| Lightly active — exercise 1–3 days/week | 1.375 |
| Moderately active — exercise 3–5 days/week | 1.55 |
| Very active — exercise 6–7 days/week | 1.725 |
| Extra active — hard exercise or a physical job | 1.9 |
Most people overestimate how active they are, so if you sit at a desk most of the day and train a few times a week, "lightly active" or "moderately active" is usually the honest choice.
Consider a 30-year-old woman who is 170 cm tall, weighs 80 kg, and wants to reach 70 kg in about three months (say 92 days). First, the weight to lose is 80 − 70 = 10 kg, which is 10 × 7,700 = 77,000 calories in total. Spread over 92 days, the daily deficit is:
Daily deficit = 77,000 ÷ 92 ≈ 837 kcal/day
Her BMR is 10 × 80 + 6.25 × 170 − 5 × 30 − 161 = 1,551.5 kcal. If she is lightly active (factor 1.375), her TDEE is about 1,551.5 × 1.375 ≈ 2,133 kcal, so her target intake would be about 2,133 − 837 ≈ 1,296 kcal per day. These are the calculator's default inputs, so you can press Calculate to see the full plan and then enter your own numbers. A deficit of 837 calories a day is on the aggressive side, which the calculator flags — a gentler timeline would be easier to sustain.
More is not better when it comes to calorie deficits. Most experts recommend a deficit of about 300 to 500 calories per day for steady, sustainable fat loss of roughly 0.25 to 0.5 kg (0.5 to 1 lb) per week. Larger deficits can work in the short term but come with real downsides: persistent hunger and fatigue, loss of muscle mass, nutrient shortfalls, and a metabolism that adapts by slowing down. As a safety floor, adults generally should not eat below about 1,200 calories a day for women or 1,500 for men without medical supervision, because it becomes very hard to meet nutritional needs. The calculator warns you if your chosen timeline pushes the target intake below these levels, so you can extend your target date to a healthier pace.
The math of "7,700 calories per kilogram" gives an excellent planning estimate, but real bodies are more complicated. As you lose weight, your TDEE falls — a smaller body burns fewer calories — so a deficit that produced fast loss at the start slows down over time, a phenomenon sometimes called a plateau. Water weight, glycogen stores, hormones, sleep, stress, and the makeup of your diet all cause day-to-day fluctuations that can mask real fat loss. Individual metabolism varies too, so two people following the same plan may see different results. Treat the calculator's numbers as a reliable starting point, weigh yourself consistently, and adjust your intake by 100 to 200 calories if your progress stalls or races ahead.
A successful deficit is one you can actually stick to, so the quality of your calories matters as much as the quantity. Prioritise protein, which preserves muscle while you lose fat and keeps you feeling full; aim to include a protein source at every meal. Fill your plate with vegetables and fruit for volume, fibre, and micronutrients at a low calorie cost, and choose whole, minimally processed foods that satisfy hunger better than refined snacks. Stay hydrated, since thirst is easily mistaken for hunger, and be mindful of liquid calories in sodas, juices, and alcohol, which add up quickly without filling you up. Small, consistent habits — planning meals, watching portion sizes, and keeping tempting foods out of easy reach — make a moderate deficit feel almost effortless over time.
You can create a calorie deficit by eating less, moving more, or both — and combining the two is usually the most effective and healthiest approach. Cutting calories does the heavy lifting for weight loss, while exercise, especially resistance training, protects the muscle you want to keep and raises the number of calories you burn each day. Cardio adds to your deficit and benefits your heart, and simply being more active in daily life — walking, taking the stairs, standing more — quietly increases your expenditure. Rather than relying on exercise alone to burn off large amounts of food, use it to support a moderate dietary deficit; that partnership tends to produce better body composition and is far easier to maintain.
Every eating plan sits in one of three energy states relative to the calories your body burns. At maintenance, you eat exactly what you expend and your weight holds steady — this is your TDEE. In a calorie deficit, you eat below maintenance, so your body draws on stored fat and you lose weight. In a calorie surplus, you eat above maintenance, providing extra energy that supports weight and muscle gain. The three are simply points on a single scale, and knowing your maintenance number is the anchor for all of them: subtract from it to lose, add to it to gain. This calculator focuses on the deficit needed to reach a lower goal weight, but if your target weight is higher than your current weight it will show the daily surplus instead, because the same arithmetic works in both directions. Understanding where you sit on this scale turns weight management from guesswork into a deliberate, adjustable plan.
A calorie deficit is a starting hypothesis, not a guarantee, so it pays to measure and adjust. Weigh yourself under consistent conditions — ideally first thing in the morning, a few times a week — and pay attention to the weekly average rather than any single reading, since day-to-day changes are mostly water and food in transit. Give any change at least two to three weeks before judging it, because that is long enough to see through the noise. If your weight is falling faster than planned and you feel drained, ease the deficit by eating a little more; if it has stalled for a few weeks despite honest tracking, trim your intake by 100 to 200 calories or add some activity. Because your TDEE drops as you lose weight, recalculating your numbers every few kilograms keeps your targets realistic. This feedback loop — plan, measure, adjust — is what separates people who reach their goal from those who stall and give up.
Several avoidable errors derail otherwise good plans. The biggest is cutting too hard: a very aggressive deficit brings hunger, fatigue, muscle loss, and a metabolism that fights back, making the plan impossible to sustain. Another is underestimating intake — untracked snacks, cooking oils, drinks, and generous portions can quietly erase a deficit, which is why honest measuring matters more than any formula. Many people also overestimate how many calories exercise burns and then "eat back" more than they spent, wiping out the gap. Neglecting protein is a further trap, since too little accelerates muscle loss during weight loss. Finally, expecting perfectly linear results and panicking at the first plateau leads people to quit just as their bodies are adjusting. Sidestep these mistakes — keep the deficit moderate, track accurately, prioritise protein, and stay patient — and the numbers in this calculator will translate into steady, lasting progress.
Work out your TDEE (BMR × activity factor), then subtract the calories you eat. The calculator instead starts from your weight goal: it multiplies the kilograms to lose by 7,700 and divides by the days until your target date to give the daily deficit.
A deficit of about 300–500 calories a day gives steady, sustainable loss of roughly 0.25–0.5 kg (0.5–1 lb) per week. Larger deficits are harder to maintain and can cost you muscle.
About 7,700 calories per kilogram, or roughly 3,500 calories per pound. That is why a 3,500-calorie weekly deficit loses about one pound of fat.
A 1,000-calorie daily deficit is aggressive and only advisable for some people under guidance. Never eat below about 1,200 calories (women) or 1,500 (men) a day without medical supervision.
Common reasons include underestimating intake, water-weight fluctuations, a falling TDEE as you lose weight, or an inaccurate activity estimate. Track consistently and adjust your intake if progress stalls for a few weeks.
Yes. Weight loss is driven by the calorie deficit, which you can create through diet alone. Exercise helps by protecting muscle, raising your expenditure, and improving health, but it is not strictly required to lose weight.
This Calorie Deficit Calculator is provided for general informational and educational purposes and gives estimates based on the Mifflin-St Jeor equation and the standard 7,700 kcal-per-kilogram figure. It is not medical or nutritional advice. Individual results vary, and you should consult a qualified health professional before starting any weight-loss program, especially if you have a medical condition.