Calorie deficit calculator
A calorie deficit is the gap between the calories your body burns in a day and the calories you actually eat: stay below your burn and your body taps stored fat to cover the difference.
- Based on standard published formulas
- Instant, easy-to-read estimates
- Private: nothing leaves your device
Calorie deficit calculator
Enter your numbers and press Calculate
How to use this calculator step by step
The calculator walks you through six quick steps. Fill each field in order and the results update instantly.
1. Weight (kg). Weigh yourself first thing in the morning, before breakfast. If your scale reads pounds, divide by 2.2046 to get kilograms (198 lb ≈ 90 kg). 2. Height (cm). One inch is 2.54 cm, so 5'11" is about 180 cm. 3. Age. Resting metabolism drops roughly 50 kcal per decade, so this field matters more than most people think. 4. Sex. The equation adds +5 for men and subtracts 161 for women, reflecting average differences in lean mass. 5. Activity factor. Be honest with yourself: a desk job plus three gym sessions a week is 1.375, not 1.55. Only construction workers, servers on their feet all day, or daily athletes should go above 1.55. 6. Deficit (%). Start at 15-20%. That usually lands close to the classic "500 calories a day" rule without starving you.
Once everything is filled in you'll see four numbers: your BMR (what you burn at complete rest), your TDEE (total burn including activity), your daily calorie target for fat loss, and the estimated weekly loss in kilograms.
The Mifflin-St Jeor formula explained
The Mifflin-St Jeor equation (published in 1990 and endorsed by the Academy of Nutrition and Dietetics) estimates resting metabolism from weight, height, age and sex:
- Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5
- Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161
Three chained calculations follow:
- TDEE = BMR × activity factor
- Calorie target = TDEE × (1 − deficit/100)
- Weekly loss (kg) = (TDEE − target) × 7 / 7700
The 7700 figure is the approximate number of kilocalories stored in one kilogram of body fat — the metric cousin of the familiar "3,500 calories per pound" rule.
Worked example. A 45-year-old man, 90 kg (about 198 lb), 180 cm (5'11"), moderately active (1.55), aiming for a 20% deficit:
1. BMR = 10 × 90 + 6.25 × 180 − 5 × 45 + 5 = 900 + 1125 − 225 + 5 = 1805 kcal 2. TDEE = 1805 × 1.55 = 2798 kcal 3. Target = 2797.75 × 0.80 = 2238 kcal 4. Weekly loss = (2797.75 − 2238.2) × 7 / 7700 ≈ 0.51 kg (about 1.1 lb)
In plain English: eating around 2240 calories a day, he'd lose roughly a pound a week — the pace most U.S. clinical guidelines call sustainable.
Common mistakes when setting a calorie deficit
Going past a 30% deficit. Cutting more than a third of your burn spikes hunger, drains energy and accelerates muscle loss — and it doubles the odds you quit within weeks. A 40% deficit doesn't melt fat twice as fast as 20%; it just lasts half as long. That's why this calculator caps the field at 30%.
Never recalculating as you lose weight. TDEE depends on body weight: drop from 200 lb to 175 lb (about 90 to 80 kg) and the formula alone shaves roughly 140 kcal off your daily burn. Keep eating your day-one calories and your real deficit quietly shrinks until the scale stalls. Recalculate every 10 pounds lost, or once a month.
Overestimating your activity factor. This is the most expensive mistake. Walking to the parking lot and taking the stairs doesn't turn a desk job into "moderately active." When torn between two levels, pick the lower one — better to underestimate your burn than to build a plan on 300 phantom calories.
Double-counting exercise. If your activity factor already covers your three weekly workouts, don't also "eat back" the calories your smartwatch reports after each session. Fitness trackers overstate burn by 20-40% in most studies, and that double entry can turn a planned 20% deficit into plain maintenance.
Worked examples: three real-world profiles
The table shows three everyday profiles, computed with the exact formula behind this tool:
| Profile | BMR | TDEE | Target | Loss/week |
|---|---|---|---|---|
| Man, 90 kg, 180 cm, 45 y, factor 1.55, 20% deficit | 1805 kcal | 2798 kcal | 2238 kcal | 0.51 kg |
| Man, 95 kg, 183 cm, 50 y, factor 1.725, 25% deficit | 1849 kcal | 3189 kcal | 2392 kcal | 0.72 kg |
| Woman, 62 kg, 158 cm, 27 y, factor 1.375, 15% deficit | 1312 kcal | 1803 kcal | 1533 kcal | 0.25 kg |
Two things stand out. First, the very active 50-year-old can lose over 0.7 kg (about 1.6 lb) a week while still eating almost 2400 calories — activity buys you food budget. Second, the 27-year-old woman only needs a gentle 15% cut to lose roughly half a pound a week, and a harsher deficit would push her under the 1200-1500 kcal floor most U.S. guidelines treat as the minimum for women.
This calculator is for educational purposes only and is not medical or nutritional advice. Talk to your physician or a registered dietitian before starting any reduced-calorie diet.
Frequently asked questions
What percentage calorie deficit is recommended?
For most healthy adults, a 15-20% deficit below total expenditure balances visible results with long-term adherence. Below 10% progress is barely noticeable; above 25-30% hunger, fatigue and muscle loss climb fast, and plans rarely survive more than a few weeks. That's why this calculator caps the deficit at 30%.
Where does the 7,700 kcal per kilogram figure come from?
A kilogram of adipose tissue is roughly 87% pure lipid, and each gram of fat stores about 9 kcal: 870 g × 9 kcal ≈ 7,800, which the literature rounds to 7,700 kcal — the metric version of the classic 3,500-calories-per-pound rule. It's a useful approximation, not an exact law: water, glycogen and some lean mass shift too, so the scale swings more than the formula, especially in the first two weeks.
How often should I recalculate my calories?
Recalculate every 4-5 kg (roughly every 10 pounds) lost, or at least once a month. Total expenditure depends on body weight: as you slim down, your TDEE drops and the deficit you set on day one quietly shrinks. If you've stalled for two or three weeks while sticking to the plan, the fix is usually updating the numbers — not slashing calories blindly.
How accurate is the Mifflin-St Jeor equation?
In validation studies it lands within ±10% of metabolism measured by calorimetry for most adults, outperforming the older Harris-Benedict equation. Its main blind spot is body composition: a very muscular person burns more than predicted, someone with little lean mass burns less. Treat the output as a starting point and adjust based on how your weight actually trends over 3-4 weeks.
About this calculator
This calculator estimates your basal metabolic rate (BMR) with the Mifflin-St Jeor equation — the formula most dietitians in the U.S. rely on — multiplies it by your activity factor to get your total daily energy expenditure (TDEE), and then applies the deficit percentage you choose. You get a daily calorie target plus an estimate of weekly weight loss in kilograms (divide by 2.2 nowhere — we show kg, and 0.45 kg is about 1 lb). No sign-up, no $10-a-month subscription: enter your weight, height, age, sex and activity level and read your numbers instantly.