Calorie Deficit Calculator – Daily Calories to Lose Weight
Estimate the daily calories you need to lose, maintain or gain weight. Enter your sex, age, height, weight, activity level and goal to get your calorie target, pace and projected goal date.
Daily Calorie Needs by Body Weight
Required Daily Calorie Intake Formula
Where:
- \(W\) — body weight (kg)
- \(H\) — height (cm)
- \(A\) — age (years)
- \(s\) — sex constant: \(+5\) for men, \(-161\) for women
- \(k\) — activity factor (1.2 to 1.9)
- \(p\) — chosen pace of weight change (kg per week)
- \(C\) — required daily calorie intake (kcal/day)
The first line is the Mifflin–St Jeor basal metabolic rate, the energy your body uses at complete rest. Multiplying by the activity factor gives TDEE, the intake that maintains your current weight. For a loss goal \(p\) is subtracted; for a gain goal it is added. Because 1 kg of body fat stores about 7,700 kcal, each 0.5 kg per week requires a daily adjustment of roughly 550 kcal (hence \(1100p\)).
Required Daily Calorie Intake – Calculation Example
Example: a 35-year-old woman, 165 cm tall, weighing 70 kg, with light activity (1.375), wants to reach 65 kg at a steady pace of 0.5 kg per week.
\[\text{BMR} = 10 \times 70 + 6.25 \times 165 - 5 \times 35 - 161 = 1395\ \text{kcal/day}\]
\[\text{TDEE} = 1395 \times 1.375 = 1918\ \text{kcal/day}\]
\[C = 1918 - 1100 \times 0.5 = 1918 - 550 = 1368\ \text{kcal/day}\]
Result: a daily target of about 1,368 kcal — a 550 kcal/day deficit. She needs to lose 5 kg (about 38,500 kcal in total), which takes 10 weeks, so starting on March 3, 2025 the goal date is around May 12, 2025.
How to use the calculator
- Choose your Sex and enter your Age (15–100 years). Both feed into the Mifflin–St Jeor equation.
- Pick a Height format — centimeters or feet and inches — and enter your Height. If you choose feet and inches, two extra fields appear.
- Enter your current Weight (W) and pick kg or lb as the unit.
- Select the Activity level that best matches your typical week, from Sedentary (1.2) to Extra active (1.9).
- Choose a Goal: lose, maintain or gain weight. For Maintain weight the result is simply your maintenance intake (TDEE).
- If your goal is to lose or gain, enter a Goal weight (Wg), a Weight-loss / gain pace and a Start date. The projection counts from that date.
- Read the Daily calorie target and the Goal projection, which shows the weight to change, the deficit or surplus, the expected duration and the estimated goal date.
What your daily calorie target means
Your body burns energy around the clock: keeping your heart beating, lungs breathing and body temperature stable (basal metabolism), plus everything you physically do. The Mifflin–St Jeor equation estimates the resting part from your weight, height, age and sex; the activity factor scales it up to a full day. The result — total daily energy expenditure (TDEE) — is the intake that would keep your weight roughly unchanged.
To lose weight you must eat less than your TDEE, creating a calorie deficit, so the body draws on stored fat. To gain weight you do the opposite. The deficit is what drives the change, not any particular food: a 550 kcal/day deficit produces the same energy shortfall whether it comes from smaller portions, fewer snacks or more movement. The Daily Energy Expenditure calculator digs deeper into where your calories go.
Interpret the projection as a plan, not a promise. Real weight loss is rarely a straight line — water retention, hormones and digestion can swing the scale by a kilogram or more in a day. Weigh yourself weekly, compare your actual trend with the projection after 3–4 weeks, and adjust the target if you are consistently faster or slower than expected. The Weight Loss Percentage calculator is a convenient way to track that progress.
Assumptions, limitations and practical tips
| Activity level | Factor | Typical day |
|---|---|---|
| Sedentary | 1.2 | Desk job, little or no exercise |
| Lightly active | 1.375 | Light exercise 1–3 days/week |
| Moderately active | 1.55 | Moderate exercise 3–5 days/week |
| Very active | 1.725 | Hard exercise 6–7 days/week |
| Extra active | 1.9 | Physical job or intense daily training |
- Safety floor. For weight loss the calculator never suggests a target below 1,200 kcal/day for women or 1,500 kcal/day for men. If your chosen pace would go below that, the target is raised and the projection is recalculated at the slower, safer pace — expect a warning in the results.
- Pace matters. Losing more than about 1% of your body weight per week is difficult to sustain and can cost muscle, which lowers your metabolic rate. The calculator flags such paces automatically; 0.5–1% per week is typical.
- Adaptation. As you lose weight your TDEE falls, so a target that worked at the start becomes too generous later. Re-run the calculation with your updated weight every 5 kg or so, or plan calories for your goal weight.
- Estimates, not measurements. Mifflin–St Jeor is accurate to within roughly 10% for most people, but individual needs vary. Formulas like Katch-McArdle or Harris-Benedict can give slightly different values, which is a normal sign of estimation error, not a contradiction.
- Food quality and health. A calorie target says nothing about nutrients. Keep enough protein while dieting to protect muscle, and consult a doctor or dietitian before starting if you are pregnant, breastfeeding, under 18, or managing a medical condition.
Frequently Asked Questions
How do I calculate my calorie deficit by hand?
First estimate your maintenance intake (TDEE) with the Mifflin–St Jeor equation, then subtract your daily deficit. Since \(1\) kg of body fat stores about 7,700 kcal, losing \(p\) kg per week needs a daily deficit of about \(1100p\) kcal. Example: if your maintenance is 2,000 kcal/day and you want to lose 0.5 kg per week, your target is \(2000 - 1100 \times 0.5 = 1450\) kcal/day. One pound per week corresponds to roughly a 500 kcal daily deficit.
How many calories should I eat to lose 1 lb per week?
A deficit of about 500 kcal per day generally produces roughly 1 lb (0.45 kg) of fat loss per week, because 1 lb of body fat stores about 3,500 kcal. So if your maintenance intake is, say, 2,300 kcal/day, eating around 1,800 kcal/day should yield about 1 lb per week. For 2 lb per week you would double the deficit — but very large deficits are harder to sustain and the calculator flags paces above 1% of body weight per week.
Why is 1 kg of body fat equal to 7,700 kcal?
Pure fat contains about 9 kcal per gram, and body fat is roughly 87% actual lipid, so 1 kg stores approximately \(1000 \times 9 \times 0.87 \approx 7700\) kcal. This is an average: early weight loss also includes water and glycogen, which is why the scale often drops faster in the first week or two. Over weeks and months the 7,700 kcal rule is a reasonable planning figure.
Is it safe to eat below my BMR?
Losing weight means eating below your TDEE, which may fall below your BMR at aggressive paces. For most healthy adults this is not automatically dangerous over a moderate period, but very low intakes risk muscle loss, nutrient shortfalls and fatigue. This calculator applies a floor of 1,200 kcal/day for women and 1,500 kcal/day for men and slows the projected pace rather than suggesting anything lower. If you need a target below that, do it only under medical supervision.
Should I choose my activity level based on my workouts alone?
No — the factor covers your whole day, not just exercise. A desk worker who hits the gym three times a week is still usually 'lightly active' (1.375), because BMR plus daily movement dominates the total. Overestimating activity is one of the most common mistakes and makes the maintenance figure (and any deficit built on it) too generous. If you add a workout but also get lazier the rest of the day, your TDEE may barely change.
Why did my weight loss stall even though I kept the same calorie target?
As you lose weight your BMR and TDEE fall, so a deficit that worked at the start becomes smaller — and your real intake is often a bit higher than tracked. Plateaus of 2–3 weeks are also common due to water retention and normal fluctuation, so first check the weekly trend, not daily readings. After 3–4 stalled weeks, re-run the calculator with your current weight (the page recalculates automatically) or reduce intake by 100–200 kcal/day and reassess.
How accurate are these calorie estimates, and what about other formulas?
Mifflin–St Jeor is accurate to within roughly 10% for most adults, but individual needs vary with genetics, muscle mass and health conditions. Other equations — Harris–Benedict (older, tends to run higher) and Katch–St Jeor/Katch–McArdle (uses lean mass, best if you know your body fat percentage) — can give results differing by a few hundred kcal, which is normal estimation spread, not a contradiction. Treat any figure as a starting point and adjust it based on 3–4 weeks of actual weight-trend data.