Most people lose weight at a safe, sustainable rate of about 0.5–1 kg (1–2 lb) per week, so a 5 kg (11 lb) goal usually takes roughly 5–10 weeks and a 10 kg (22 lb) goal about 10–20 weeks. Heavier people often lose faster at the start. Your actual timeline depends on how large a calorie deficit you can hold, how your body adapts, and how consistent you stay. This guide covers the math, realistic timelines, and why the scale never moves in a straight line.
The math behind fat loss
One kilogram of body fat stores roughly 7,700 kcal of energy (about 3,500 kcal per pound). To lose it you have to burn more energy than you take in over time, which is called a calorie deficit. Divide fat's energy content by your daily deficit and you get a rough timeline.
A daily deficit of about 550 kcal adds up to roughly 3,850 kcal per week, close to half a kilogram (just over 1 lb) of fat. Double it to around 1,100 kcal per day and, in theory, you approach 1 kg (2 lb) per week. Those two numbers bracket the commonly recommended range.
It helps to know your own figures first. Start with your basal metabolic rate to see how much energy your body uses at rest, then estimate your total daily energy expenditure with a TDEE calculator. Your deficit is the gap between the calories you burn and the calories you eat, so knowing your maintenance level turns that gap into a concrete number instead of a guess.
Worked examples: how long common goals take
Here is how the arithmetic plays out for realistic targets at two steady paces:
- Lose 5 kg (11 lb): about 10 weeks at 0.5 kg/week, or about 5 weeks at 1 kg/week.
- Lose 10 kg (22 lb): about 20 weeks (roughly 5 months) at 0.5 kg/week, or about 10 weeks at 1 kg/week.
- Lose 15 kg (33 lb): about 30 weeks at 0.5 kg/week, or about 15 weeks at 1 kg/week.
- Lose 20 kg (44 lb): about 40 weeks (close to 9 months) at 0.5 kg/week.
These are planning estimates, not promises. Real progress wobbles week to week because of water, gut contents, hormones, and training. To turn your own starting weight, goal, and deficit into a personalised finish date, use the weight loss timeline calculator to project your goal date instead of doing the sums by hand.
Why bigger people lose faster at first
Someone who weighs 120 kg (265 lb) burns considerably more energy each day than someone who weighs 70 kg (154 lb), because a larger body costs more to move and maintain. A heavier person therefore has a bigger maintenance level to cut from and can run a larger deficit while still eating a reasonable amount of food. Losing 1 kg (2 lb) or more per week early on is common in this situation.
As weight comes down, so does daily energy expenditure. The same eating pattern that produced a 900 kcal deficit at 120 kg (265 lb) might only produce a 500 kcal deficit at 90 kg (198 lb). Progress that felt fast in month one naturally cools off later. That is normal and expected, not a sign of failure.
Why weight loss slows over time
Two forces bend the graph away from a straight line. The first is the shrinking-body effect above: a lighter you needs fewer calories, so a fixed intake produces a smaller deficit as the weeks pass. The second is adaptive thermogenesis, also called metabolic adaptation, in which the body lowers energy expenditure by more than the loss of tissue alone would predict. Resting metabolism dips modestly, and unconscious movement such as fidgeting and general daily activity often falls too. Studies of dieters show reductions in energy expenditure beyond what the loss of body mass accounts for.
The practical takeaway is that the deficit you calculated on day one gradually erodes. Preserving muscle blunts this: strength training plus enough protein helps protect lean mass during a diet, and setting your intake with a macro calculator makes it easier to hit a protein target while staying in a deficit.
Water weight and the fast first two weeks
The scale often drops sharply in the first one to two weeks, and much of that early change is water, not fat. When you eat fewer carbohydrates, your body burns through stored glycogen, and each gram of glycogen holds several grams of water with it. Lower salt intake and less food volume in the digestive tract add to the effect. Seeing 1–3 kg (2–7 lb) disappear quickly is common, followed by a slowdown to a steadier, fat-based rate. That fast start is encouraging, but do not use it to forecast the whole journey; the sustainable rate is what shows up from about week three onward.
Plateaus are normal
A plateau, where the scale stalls for two or more weeks despite consistent effort, happens to almost everyone. Usually it means your deficit has quietly closed: your smaller body burns less, adaptation has trimmed expenditure further, and portion sizes may have crept up. The fix is to recalculate, not to panic. Re-estimate your maintenance calories at your current weight, then set a modest deficit from that new baseline. Tightening up food tracking, adding some activity, or taking a brief maintenance break can all help. Rechecking your targets every 4–5 kg (about 10 lb) of loss keeps the plan matched to your current body.
Reference table: weekly rate, monthly loss, and daily deficit
| Weekly rate | Approx. monthly loss | Approx. daily deficit | Best suited to |
|---|---|---|---|
| 0.25 kg / 0.5 lb | 1 kg / 2 lb | ~275 kcal | Lean people; final few kg |
| 0.5 kg / 1 lb | 2 kg / 4.5 lb | ~550 kcal | Most people; sustainable default |
| 0.75 kg / 1.5 lb | 3 kg / 6.5 lb | ~825 kcal | Higher starting weight |
| 1 kg / 2 lb | 4 kg / 9 lb | ~1,100 kcal | Higher starting weight, supervised |
Figures are rounded approximations based on roughly 7,700 kcal per kg (3,500 kcal per lb) of fat; individual results vary with body size, activity, and metabolic adaptation.
Sustainable beats fast
Crash diets can move the scale quickly, but health authorities favour a gradual pace because it protects muscle, is easier to keep up, and is linked to better long-term results. The CDC notes that people who lose weight steadily, at about 1–2 lb per week, are more likely to keep it off. A slightly smaller deficit you can hold for months usually beats an aggressive one you abandon in three weeks. Pick a rate you can live with, keep meals you actually enjoy, and let consistency do the work.
This article is general information, not medical advice. If you have a medical condition, are pregnant, or take medication, talk with a qualified healthcare professional before starting a weight-loss plan.
Key sources: CDC Healthy Weight (Steps for Losing Weight); NHS Weight Loss Plan; World Health Organization guidance on obesity and healthy diet; National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) on weight management and energy balance; peer-reviewed research on metabolic adaptation during weight loss; and Hall & Chow (2013) on the limits of the 3,500-kcal rule.