A calorie deficit simply means eating fewer calories than your body burns each day. A daily deficit of about 500 calories typically leads to around 0.5 kg (1 lb) of fat loss per week — and you can calculate your personal number in three steps: find your BMR, estimate your TDEE, then subtract your deficit. This guide walks you through the exact math with a worked example.
Answer a few questions and our calorie deficit calculator will estimate your BMR, TDEE and daily calorie target automatically.
Calculate My DeficitYour body burns calories around the clock — keeping your heart beating, your brain running, digesting food, and powering every step you take. The total number of calories you burn in a day is called your Total Daily Energy Expenditure (TDEE). When you consistently eat fewer calories than your TDEE, your body makes up the difference by breaking down stored fat. That gap is the calorie deficit, and it is the single mechanism behind virtually all sustained fat loss.
No food is magically "fattening" and no food burns fat on its own. Diets work — when they work — because they create this deficit, whether through smaller portions, fewer sugary drinks, intermittent fasting, or any other approach. Understanding the numbers behind it puts you in control instead of guessing.
There are three steps. We will do them together with a real example so you can follow along with your own numbers.
Your Basal Metabolic Rate (BMR) is the number of calories your body needs at complete rest — the energy cost of simply being alive. The most widely used formula is Mifflin-St Jeor:
Example: a 35-year-old woman who weighs 75 kg and is 165 cm tall:
BMR = 10 × 75 + 6.25 × 165 − 5 × 35 − 161 = 750 + 1,031.25 − 175 − 161 = ≈ 1,445 calories/day
Rather than doing this by hand, you can calculate your BMR with our free tool — it handles both metric and imperial units.
BMR is only the starting point. To get your TDEE, multiply your BMR by an activity factor that reflects how much you move:
Example continued: our 35-year-old is lightly active, so TDEE = 1,445 × 1.375 = ≈ 1,987 calories/day. That is roughly how much she burns on a typical day. Be honest here — most people overestimate their activity, which is the most common reason a "deficit" quietly disappears. When in doubt, pick the lower tier. You can calculate your TDEE precisely with your own stats.
Finally, subtract your chosen deficit from your TDEE to get your daily calorie target:
Example continued: 1,987 − 500 = ≈ 1,487 calories/day. Eating around 1,487 calories daily should produce roughly 0.5 kg of fat loss per week for her. To see what this means for your own stats and timeline, try the daily calorie needs calculator.
Bigger is not automatically better. An aggressive deficit is harder to sustain, increases hunger, and raises the risk of losing muscle along with fat. Here is what different deficit sizes mean in practice:
| Daily deficit | Expected fat loss | Best for |
|---|---|---|
| 250 calories | ≈ 0.25 kg (0.5 lb) per week | Gentle, easy to sustain; good when you are already fairly lean |
| 500 calories | ≈ 0.5 kg (1 lb) per week | The standard recommendation for most people |
| 750 calories | ≈ 0.75 kg (1.5 lb) per week | Aggressive; suits higher starting weights and shorter phases |
| 1,000 calories | ≈ 1 kg (2 lb) per week | Upper limit — only with professional guidance |
A widely cited safe rate is 0.5–1% of your body weight per week. For our 75 kg example, that is 0.375–0.75 kg weekly — right in line with a 500-calorie deficit. As a rule of thumb, most adults should not regularly eat below about 1,200 calories/day (women) or 1,500 calories/day (men) without medical supervision, and you should avoid staying below your BMR for extended periods.
You will often hear that one pound (0.45 kg) of body fat stores roughly 3,500 calories. That is where the "500 calories × 7 days = 3,500 = one pound per week" math comes from. It is a useful planning rule, but treat it as an estimate, not physics: real weight loss is rarely perfectly linear. Water retention, glycogen shifts, and metabolic adaptation mean some weeks the scale barely moves even when fat loss is happening. Judge progress over 2–4 week trends, not day-to-day readings.
Divide your total goal by your expected weekly loss. Want to lose 10 kg at 0.5 kg per week? That is roughly 20 weeks — about five months. It sounds slow, but slow loss is far more likely to stay off than crash-diet weight. A handy check: 1 kg of body fat holds about 7,700 calories, so 10 kg ≈ 77,000 calories ÷ 500/day ≈ 154 days.
Your deficit does not have to stay fixed forever. As you lose weight, your BMR and TDEE drop slightly (a smaller body burns less), so recalculate every 4–6 weeks or whenever progress stalls for more than three weeks. The weight loss calculator builds this timeline for you from your current and target weight.
For the bigger picture — how deficits fit into overall nutrition planning — browse our full set of body and nutrition calculators.
You know the math now — let the calculator do the arithmetic with your exact stats.
Calculate My Calorie DeficitWritten by the Live Fitness Check editorial team · Reviewed against our calculator methodology · Last updated October 2026
Disclaimer: This guide is for educational purposes only and is not medical advice. Calorie needs vary by individual; consult your doctor or a registered dietitian before starting a weight-loss plan, especially if you are pregnant, nursing, managing a medical condition, or have a history of disordered eating.
