Last updated October 10, 2026 · Report an error
This calculator finds the percentage of body weight lost (or gained) between a starting and current weight — the same formula used by many weight-loss programs and challenges to compare progress fairly across people with different starting weights. This is a plain arithmetic reference calculation, not medical advice — consult a doctor before starting any weight-loss program.
How it works
Enter your starting weight and current weight (and optionally, weeks elapsed). The tool calculates the percentage change and, if weeks were provided, compares your weekly pace to the commonly cited guideline of about 0.5-1% of body weight per week.
- Enter starting weight.
- Enter current weight.
- Enter weeks elapsed (optional).
- Click Calculate to see your results.
Examples
A 90kg starting weight, now 85kg
Percent lost = (90 - 85) / 90 x 100 ≈ 5.6%.
Who should use it
- Tracking personal weight-loss progress over time.
- Comparing progress fairly in a group weight-loss challenge.
Industry applications
- Fitness and wellness coaching
- Corporate wellness programs
Advantages
- Simple, quick calculation.
- Allows fair progress comparison across different starting weights.
Limitations
- Does not distinguish fat loss from water weight or muscle changes.
- Not a substitute for professional guidance on a weight-loss plan.
Common mistakes to avoid
- Comparing raw weight lost (in kg/lb) between people of very different starting weights instead of using percentage.
- Treating short-term water-weight fluctuations as true fat loss progress.
Best practices
- Weigh yourself under consistent conditions (same time of day, similar clothing) for the most meaningful percentage tracking.
Tips
- Track weekly or monthly averages rather than single daily readings to smooth out normal day-to-day fluctuations.