Weight Loss Calculator
Enter your current weight, goal weight, and daily calorie deficit to find out how long it will take to reach your goal.
How Weight Loss Timelines Are Calculated
One kilogram of body fat contains approximately 7,700 kilocalories of stored energy (one pound of fat ≈ 3,500 kcal). To lose that fat, you need to burn more energy than you consume by that amount over time. A daily deficit of 500 kcal creates a weekly deficit of 3,500 kcal — theoretically losing about 0.5 kg (1 lb) per week.
This is a simplified model. In reality, weight loss slows as you get lighter (because a lighter body burns fewer calories), the body adapts to restriction by reducing metabolic rate, and water retention can mask fat loss on the scale. The timeline this calculator gives is a realistic estimate based on the 7,700 kcal/kg rule, useful for planning but not a guarantee.
For most people, a deficit of 500 kcal/day is sustainable and produces meaningful results without excessive hunger or muscle loss. Deficits above 1,000 kcal/day increase the risk of losing muscle mass alongside fat and are hard to maintain long-term.
Expected Weight Loss by Deficit Size
| Daily deficit | Weekly loss | Monthly loss | Sustainability |
|---|---|---|---|
| 250 kcal | ~0.23 kg (0.5 lb) | ~1 kg (2.2 lbs) | Very easy to maintain |
| 500 kcal | ~0.45 kg (1 lb) | ~2 kg (4.4 lbs) | Manageable for most people |
| 750 kcal | ~0.68 kg (1.5 lbs) | ~3 kg (6.6 lbs) | Challenging; requires planning |
| 1000 kcal | ~0.91 kg (2 lbs) | ~4 kg (8.8 lbs) | Hard to sustain; muscle loss risk |
Worked Examples
Example 1: Lose 10 kg at 500 kcal/day deficit. 10 kg × 7,700 kcal/kg = 77,000 kcal total deficit needed. 77,000 ÷ 500 = 154 days ≈ 22 weeks.
Example 2: Lose 20 lbs at 500 kcal/day deficit. 20 lbs × 3,500 kcal/lb = 70,000 kcal total deficit. 70,000 ÷ 500 = 140 days ≈ 20 weeks.
Example 3: Lose 5 kg at 250 kcal/day (slow and steady). 5 × 7,700 = 38,500 kcal. 38,500 ÷ 250 = 154 days ≈ 22 weeks. Same timeline as example 1 — half the deficit, half the weight to lose.
Frequently Asked Questions
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As you lose weight, your body requires fewer calories to function — a lighter body burns fewer calories at rest and during movement. This means your calorie deficit shrinks as you lose weight, unless you adjust your intake or increase activity. The last few kilograms are always the hardest for this reason.
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The most sustainable approach is a combination of eating slightly less and moving slightly more. For example: reduce portion sizes and cut high-calorie snacks to save 250–300 kcal, then add 30 minutes of walking or light exercise to burn another 200–250 kcal. Use our TDEE calculator to find your maintenance calories, then subtract 500.
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Some muscle loss during a calorie deficit is normal, but it can be minimised. The key strategies are: keep protein high (1.8–2.4 g/kg body weight), continue resistance training throughout the deficit, and avoid very large deficits (>1,000 kcal/day). A slow, moderate deficit with adequate protein preserves most muscle mass.
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Water retention is the most common reason. Increased sodium, carbohydrate intake, stress (cortisol), hormonal fluctuations, and starting a new exercise programme can all cause the body to retain water — masking fat loss on the scale for days or weeks. Fat loss is still happening; it just isn't visible yet. Weigh yourself daily and look at the weekly average trend rather than day-to-day readings.
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For most people, losing more than 0.5–1% of body weight per week increases the risk of muscle loss, nutritional deficiencies, fatigue, and gallstones. Faster initial loss is common in the first 1–2 weeks due to water and glycogen depletion, but sustained loss above 1 kg/week is not recommended except under medical supervision.
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Maintenance requires eating at your new TDEE — which is lower than before because you now weigh less. Many people regain weight by returning to old eating habits. The transition to maintenance is a distinct phase that requires recalibrating intake. Gradually increasing calories by 100–200 kcal/week until weight stabilises is a useful approach.