Weight Loss Percentage Calculator
Work out what percentage of your body weight you have lost, see the arithmetic behind it, and track how far you are toward a goal weight.
Weight loss percentage is weight lost ÷ starting weight × 100. Losing 9 kg from a starting weight of 90 kg is 10% — and the answer is the same in pounds, because the units cancel.
How to calculate percent weight loss
Percentage weight loss and percent weight loss are the same figure written two ways, and neither involves a model or an estimate — just one division. Take the weight you have lost, divide it by the weight you started at, and multiply by 100:
- Weight lost = starting weight − current weight
- Percentage = weight lost ÷ starting weight × 100
So a start of 90 kg and a current weight of 81 kg gives 9 ÷ 90 × 100 = 10%. The same person tracking in pounds — 198 lb down to 178 lb — gets 20 ÷ 198 × 100, which is also about 10%. That is worth knowing: because the units appear on both sides of the division, they cancel, so you never need to convert anything to compare with someone tracking in the other system.
The one thing to get right is the denominator. It is your starting weight, not your current one. Dividing by the current weight inflates the figure — in the example above it would return 11.1% instead of 10% — and it is the most common way this calculation goes wrong.
Weight loss percentage chart
What a given percentage looks like in absolute terms, across a range of starting weights.
| Starting weight | 5% | 10% | 15% | 20% |
|---|---|---|---|---|
| 60 kg (132 lb) | 3.0 kg | 6.0 kg | 9.0 kg | 12.0 kg |
| 70 kg (154 lb) | 3.5 kg | 7.0 kg | 10.5 kg | 14.0 kg |
| 80 kg (176 lb) | 4.0 kg | 8.0 kg | 12.0 kg | 16.0 kg |
| 90 kg (198 lb) | 4.5 kg | 9.0 kg | 13.5 kg | 18.0 kg |
| 100 kg (220 lb) | 5.0 kg | 10.0 kg | 15.0 kg | 20.0 kg |
| 120 kg (265 lb) | 6.0 kg | 12.0 kg | 18.0 kg | 24.0 kg |
The same percentage means very different absolute amounts depending on where you started — which is precisely why percentage is the more comparable measure.
Why percentage beats raw pounds
Ten kilograms sounds like a fixed achievement, but it is not. For someone starting at 70 kg it is 14% of their body weight; for someone starting at 140 kg it is 7%. The same number on the scale represents a change of very different magnitude, and only the percentage captures that.
It is also the unit the evidence is written in. Research and clinical guidance on weight change overwhelmingly express results as a percentage of starting weight, with 5% and 10% appearing repeatedly as reference points. Tracking the same way means you can read a study and know where you sit, instead of trying to translate someone else's kilograms into your own situation.
What the number does and does not tell you
This is a scale measurement, and the scale weighs everything: fat, muscle, water, glycogen and whatever is currently in your digestive system. Day-to-day swings of a kilogram or more are normal and mostly water. The first week of a new diet is especially misleading, because depleting stored glycogen releases the water held with it — roughly three grams of water per gram of glycogen — which drops the scale quickly with very little fat involved.
So treat a falling percentage as evidence of a trend, not of fat loss specifically. To see what is actually changing, pair it with the body fat calculator or track lean mass with the lean body mass calculator. For how long a target should realistically take, the weight-loss timeline calculator turns a weekly rate into a goal date and checks it against a healthy pace. It holds that rate constant, so treat a long projection as a best case — energy expenditure falls as you get lighter. Set the deficit itself with the calorie deficit calculator.
One important limitation: this calculator cannot distinguish loss you intended from loss you did not. Unplanned weight loss is something clinicians actively screen for, and losing roughly 5% or more of your body weight without trying is generally treated as a reason to get checked rather than a result to celebrate. If the number here is falling and you have not been dieting or training, speak with a doctor.
Sources: CDC guidance on losing weight (sustainable rate of about 1–2 lb per week); NHS guidance on unintentional weight loss; Hall & Chow, International Journal of Obesity (2013) on why simple weight-loss projections overpredict; WHO on BMI and population weight categories. Educational information, not medical advice — speak with a qualified healthcare professional about your own circumstances.
Frequently asked questions
How do you calculate weight loss percentage?
Divide the weight you have lost by your starting weight, then multiply by 100. If you started at 90 kg and now weigh 81 kg, you have lost 9 kg, and 9 ÷ 90 × 100 = 10%. The units cancel out, so the answer is identical whether you work in kilograms or pounds — starting at 200 lb and reaching 180 lb is the same 10%.
Why use a percentage instead of just pounds or kilograms?
Because it puts the loss in proportion to the body it came from. Ten kilograms is a much larger change for someone starting at 70 kg than for someone starting at 140 kg — 14% against 7%. Percentage is also how research and clinical guidance usually express weight change, so it is the figure that lets you compare your progress to published findings rather than to another individual.
What is a good weight loss percentage?
There is no single target, but the widely cited sustainable rate is about 0.5–1 kg (1–2 lb) per week, which for most people works out near 0.5–1% of body weight per week. Faster loss is possible but tends to cost more lean tissue and is harder to maintain. Research on health outcomes often uses 5% and 10% of starting weight as reference points, because meaningful changes in several markers are commonly observed around there.
Does this measure fat loss?
No — it measures scale weight, which is not the same thing. Body weight includes water, glycogen and gut contents, and those move by a kilogram or more within a single day. Early losses on a new diet are heavily water because depleting glycogen sheds the water stored alongside it. For a picture of what is actually changing, pair this with a body-fat estimate rather than reading the scale alone.
I did not mean to lose weight. Should I be concerned?
This calculator cannot tell intentional loss from unintentional, and the distinction matters. Unplanned weight loss is one of the things clinicians screen for, and a loss of roughly 5% or more of body weight without trying is generally considered a reason to get checked rather than to keep tracking. If you have not been dieting or training and the number here is moving downward, speak with a doctor.
Sources
- CDC — Losing Weight — 1–2 lb per week as a sustainable rate
- NHS — Unintentional weight loss — When unplanned weight loss warrants medical review
- Hall KD & Chow CC (2013), International Journal of Obesity — PubMed — Why the 3,500 kcal per pound rule overpredicts
- WHO — Obesity and overweight — BMI categories and population context
The thresholds and formulas used by this calculator follow the primary sources above. This tool provides general information, not personalised medical advice.