Quick Answer — How to Calculate Weight Loss Percentage
The formula: Weight lost (%) = (Starting weight − Current weight) ÷ Starting weight × 100.
Weekly rate: Weekly rate (%) = Weight lost (%) ÷ Weeks elapsed. Most public-health and clinical sources describe roughly 0.5% to 1% of body weight per week as a gradual, sustainable pace for someone who has weight to lose safely.
Quick reference:
- 200 lb → 190 lb over 8 weeks → 5.00% lost, 0.625%/week (within the commonly cited range)
- 150 lb → 144 lb over 12 weeks → 4.00% lost, 0.333%/week (below the range — a slower, still valid pace)
- 180 lb → 165 lb over 8 weeks → 8.33% lost, 1.042%/week (above the range — worth discussing with a doctor if it continues)
Worked example: going from 200 lb to 190 lb is (200 − 190) ÷ 200 × 100 = 5.00% of starting body weight. Spread over 8 weeks, that's 0.625% per week — squarely inside the range most sources describe as gradual and sustainable.
This calculator reports where a rate falls relative to that commonly cited range. It is a reference point for context, not a target to chase — plenty of healthy, successful weight changes happen more slowly than 0.5% a week, and a rate above 1% is not automatically a problem for a short stretch, but a sustained pace above it is worth mentioning to a doctor or registered dietitian.