Work out your daily calorie deficit, your expected weekly weight loss, and an estimated date to reach your goal weight — based on the Mifflin-St Jeor formula.
A calorie deficit is simply eating fewer calories than your body burns in a day (your TDEE, or Total Daily Energy Expenditure). This calculator first estimates your TDEE from your BMR and activity level, then subtracts a percentage — 10%, 15%, 20% or 25% — to give you a daily calorie target. Hold that target consistently and the shortfall is drawn from stored body fat, at a rate of roughly 7,700 kcal per kilogram lost.
| Deficit level | Target kcal/day | Daily deficit | Est. weekly loss |
|---|
A calorie deficit calculation builds on your BMR and TDEE, then subtracts a percentage to set your daily target.
Using a fixed reference person — a 35-year-old man, 175 cm, moderately active — here's how the 20% deficit target scales with starting body weight. Your own number will differ with your age, height, sex and activity level; use the calculator above for your figures.
| Body weight | BMR | TDEE | Target (20% deficit) |
|---|---|---|---|
| 60 kg | 1,524 kcal | 2,362 kcal | 1,890 kcal/day |
| 70 kg | 1,624 kcal | 2,517 kcal | 2,014 kcal/day |
| 80 kg | 1,724 kcal | 2,672 kcal | 2,138 kcal/day |
| 90 kg | 1,824 kcal | 2,827 kcal | 2,262 kcal/day |
| 100 kg | 1,924 kcal | 2,982 kcal | 2,386 kcal/day |
Regardless of how you arrive at it, the size of your daily deficit is what drives your rate of loss. Using the standard 7,700 kcal-per-kilogram approximation:
| Daily deficit | Estimated weekly loss |
|---|---|
| 200 kcal/day | 0.18 kg/week |
| 300 kcal/day | 0.27 kg/week |
| 400 kcal/day | 0.36 kg/week |
| 500 kcal/day | 0.45 kg/week |
| 600 kcal/day | 0.55 kg/week |
| 750 kcal/day | 0.68 kg/week |
| 1,000 kcal/day | 0.91 kg/week |
It's tempting to assume that cutting harder gets you to your goal faster, and in pure arithmetic terms it does. But a very large deficit — well beyond 25% below TDEE — tends to work against you in three practical ways. First, the bigger the shortfall, the more likely your body is to break down lean muscle alongside fat, which is the opposite of what most people actually want. Second, hunger and fatigue scale roughly with deficit size, and a plan you can't stick to for more than a week or two isn't really a plan. Third, aggressive cuts leave little room for a bad day, a social event, or normal appetite fluctuation, which tends to produce an all-or-nothing cycle of strict dieting followed by overeating. A deficit in the 10–20% range, held consistently for months, generally beats a 30%+ deficit abandoned after a fortnight.
There's no single "correct" deficit — it depends on how much you want to lose, how quickly, and how sustainable the plan needs to be. A 10% deficit is gentle and easy to maintain alongside a normal social life, but produces slow results. A 20% deficit is the level most general weight-loss guidance gravitates towards, offering a reasonable balance between visible progress and day-to-day liveability. A 25% deficit accelerates results but demands more discipline and carries more risk of muscle loss if protein intake and resistance training aren't also in place. Whatever level you choose, avoid setting a target below your BMR — that's the energy your body needs just to keep its organs running, and eating consistently under it is neither pleasant nor sustainable.
| Deficit | Typical use case | Trade-off |
|---|---|---|
| Mild — 10% | Gentle, long-term fat loss alongside a busy life | Slow but easy to sustain and reverse if needed |
| Moderate — 15% | Steady loss without heavy restriction | Good balance for most people new to dieting |
| Standard — 20% | The most common general weight-loss target | Noticeable weekly progress, still workable day to day |
| Aggressive — 25% | Time-limited cuts, e.g. before an event | Faster loss, but higher hunger and muscle-loss risk |
Your BMR is the calories your body burns at complete rest. Your TDEE multiplies that by an activity factor to estimate your full daily burn — this is your maintenance level. Your target daily calories is TDEE minus your chosen deficit percentage. The weekly loss estimate converts your daily shortfall into an expected rate of fat loss using the standard energy-density approximation, and the goal date projects that rate forward from today to your goal weight. Treat all of these as informed estimates to test against your own results over several weeks, not exact predictions.
How many calories should I cut to lose weight?
Most people do well starting with a 15–20% deficit below their TDEE (maintenance calories). For a 70kg moderately active man with a TDEE of about 2,556 kcal, a 20% deficit means eating around 2,045 kcal a day — a cut of roughly 511 kcal. Smaller deficits (10%) are gentler and easier to sustain; larger ones (25%) work faster but are harder to stick to and carry a greater risk of muscle loss.
What is a safe calorie deficit?
A deficit of 10–20% below TDEE is generally considered a sustainable range for most healthy adults, translating to roughly 0.2–0.5 kg of loss per week depending on your size and activity level. Deficits beyond 25% become harder to maintain long-term and increase the risk of losing lean muscle along with fat. If you have any underlying health condition, check with your GP or an accredited dietitian before starting a structured deficit.
How long will it take to lose 5kg?
It depends on your deficit size. Using our worked example — a 70kg, 30-year-old, 175cm man at moderate activity with a 20% deficit — the daily deficit is about 511 kcal, giving an estimated 0.46 kg of loss per week. Losing 5kg at that rate takes roughly 10.8 weeks, or about two and a half months. A larger deficit shortens the timeline but is harder to sustain and less kind to your body.
What's the difference between TDEE and a calorie deficit?
TDEE is your maintenance level — the calories your body burns in a day and needs to keep your weight stable. A calorie deficit is what happens when you eat less than that. This calculator first estimates your TDEE using the Mifflin-St Jeor formula, then subtracts your chosen percentage to give you a daily calorie target for weight loss.
Why isn't a bigger deficit always better?
Very large deficits (well above 25%) increase the risk of losing muscle along with fat, tend to increase hunger and fatigue, and are harder to sustain for more than a few weeks. A moderate, sustainable deficit that you can maintain consistently for months usually beats an aggressive one you abandon after a fortnight.
How is weekly weight loss estimated from a calorie deficit?
We use the standard approximation that roughly 7,700 kcal of sustained deficit corresponds to about 1kg of body fat. Multiplying your daily deficit by 7 (days) and dividing by 7,700 gives an estimated weekly loss in kilograms. For example, a 500 kcal/day deficit works out to about 0.45 kg per week (500 × 7 ÷ 7,700).
Should I keep the same deficit the whole time I'm losing weight?
Not necessarily. As you lose weight your TDEE falls too, because a lighter body needs less energy — so the same calorie target becomes a smaller deficit over time. Recalculating every few kilograms lost, and adjusting your target accordingly, keeps your rate of loss roughly on track.
Is a calorie deficit calculator accurate?
It gives a reasonable estimate based on population formulas, not an exact personal reading. Individual metabolism, muscle mass, hormones, and even sleep and stress can shift your real numbers up or down. Use the result as a starting point, track your weight over two to three weeks, and adjust your calorie target based on the actual trend.