About the Weight Change Calculator
What this tool does
This tool answers a simple question: how much did weight change between two measurements, in absolute and percentage terms?
Adding dates lets you see average change per day and per week. Those averages are arithmetic summaries of the interval you enter.
What inputs are required
- Starting weight and ending weight (with units).
- Optional start and end dates for rate-of-change estimates.
How the result is calculated
- Absolute change = end − start after unit alignment.
- Percentage change = absolute change ÷ start × 100.
- With dates, per-day and per-week averages divide the absolute change by the elapsed time.
What the result means
- Negative values indicate loss; positive values indicate gain over the interval.
- Percentage change helps compare progress across different starting weights.
- Average rates describe the interval only — they do not predict the future.
Important limitations
- Day-to-day weight often moves with fluid, glycogen, and gut contents.
- Two-point comparisons miss mid-interval fluctuations.
- The calculator does not attribute change to fat, muscle, or water.
When professional guidance may be useful
- Bring multi-week logs to clinical visits rather than single comparisons when possible.
- Unexplained large changes warrant medical evaluation.