How to Calculate Weight Loss Percentage
Weight loss percentage tells you what fraction of your original body weight you have shed. The formula is straightforward:
Weight Loss % = ((Starting Weight − Current Weight) / Starting Weight) × 100
For example, if you started at 90 kg and now weigh 75 kg:
- Weight lost = 90 − 75 = 15 kg
- Ratio = 15 / 90 = 0.1667
- Weight loss % = 0.1667 × 100 = 16.67%
Using a percentage rather than an absolute number makes it easier to compare progress across people of different starting sizes. Losing 10 kg means something very different for someone who started at 65 kg compared with someone who started at 130 kg.
Why Percentage Matters More Than Absolute Weight
Clinical guidelines for weight management are usually expressed in percentage terms because the health benefits are proportional to starting body mass. The 5% and 10% thresholds are particularly well studied. Research published in journals including Obesity and Diabetes Care consistently shows that a 5% reduction in body weight produces meaningful improvements in:
- Fasting blood glucose and insulin sensitivity
- Blood pressure (systolic and diastolic)
- Triglyceride and HDL cholesterol levels
- Joint load and mobility
- Sleep apnoea severity
Reaching 10% of starting body weight lost is associated with even greater improvements in these markers and a measurable reduction in the risk of developing type 2 diabetes.
Common Weight Loss Milestones
| Milestone | Starting weight: 80 kg | Starting weight: 100 kg | Starting weight: 120 kg |
|---|
| 5% lost | 4 kg (reach 76 kg) | 5 kg (reach 95 kg) | 6 kg (reach 114 kg) |
| 10% lost | 8 kg (reach 72 kg) | 10 kg (reach 90 kg) | 12 kg (reach 108 kg) |
| 15% lost | 12 kg (reach 68 kg) | 15 kg (reach 85 kg) | 18 kg (reach 102 kg) |
| 20% lost | 16 kg (reach 64 kg) | 20 kg (reach 80 kg) | 24 kg (reach 96 kg) |
Worked Example
Using the calculator's default values: starting weight 90 kg, current weight 75 kg.
- Weight lost = 90 − 75 = 15 kg
- Weight loss % = (15 / 90) × 100 = 16.67%
- This exceeds the clinically meaningful 5% and 10% milestones
- 5% of 90 kg = 4.5 kg (milestone reached at 85.5 kg)
- 10% of 90 kg = 9 kg (milestone reached at 81 kg)
- 15% of 90 kg = 13.5 kg (milestone reached at 76.5 kg)
- At 75 kg you have lost 16.67% of your starting weight (16% of 90 kg = 14.4 kg, which you have passed)
Using Pounds Instead of Kilograms
The percentage formula works exactly the same way in pounds. If you started at 200 lbs and now weigh 170 lbs, your weight loss is 30 lbs. Divide 30 by 200 to get 0.15, then multiply by 100 for a weight loss percentage of 15%. The unit does not matter as long as you use the same unit for both starting and current weight.
Rate of Loss and What Is Healthy
Most health authorities recommend aiming for a loss of 0.5 to 1 kg per week (about 1 to 2 lbs per week). This is typically achieved through a calorie deficit of 500 to 1,000 kcal per day, either by eating less, moving more, or a combination of both. Very rapid weight loss beyond this rate is generally associated with a higher proportion of muscle loss, nutrient gaps, and difficulty sustaining the result. Slower, consistent progress gives the body time to adapt and tends to result in better long-term maintenance.
Related Calculators
Method: Standard weight loss percentage formula: Weight Loss % = ((Starting Weight − Current Weight) / Starting Weight) × 100. Health milestone thresholds (5%, 10%) are consistent with guidelines from the World Health Organization, the American Diabetes Association, and the National Institutes of Health.
This calculator is for informational purposes only and does not constitute medical advice. Weight management goals should be discussed with a registered healthcare professional or dietitian who can take your individual health status into account.
