Weight Change Percentage
Divide the difference by the earlier weight. The percentage matters more than the kilograms: 3 kg off a 50 kg frame is not the same event as 3 kg off 100 kg.
Your numbers
Change
-7.69%
Difference
-6kg
Loss a week
0.46kg
What it means
A drop of 7.7% within six months is the level clinicians flag if it was not intentional.
Formula
Change = (Weight now (kg) − Weight before (kg)) ÷ Weight before (kg) × 100
Unintentional loss above 5% in six months, or 10% in a year, is treated as a signal worth investigating.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Weight before (kg) (kg)Your weight when the comparison starts. | 78 | 1 and up |
| Weight now (kg) (kg)Today’s weight; measure at the same time and dress for comparison. | 72 | 1 and up |
| Months (mo)The period counted in months; a yearly rate gets divided by twelve. | 3 | 1 and up |
Step by step
Quick reference table
Results when only Weight before (kg) (kg) changes and everything else stays put.
| Weight before (kg) (kg) | Change (%) | Difference (kg) | Loss a week (kg) |
|---|---|---|---|
| 39 | 84.62 | 33 | -2.53 |
| 58.5 | 23.08 | 13.5 | -1.04 |
| 78 | -7.69 | -6 | 0.46 |
| 117 | -38.46 | -45 | 3.45 |
| 156 | -53.85 | -84 | 6.44 |
What each result means
| Result | At default values |
|---|---|
| Change (%)How far it moved, measured against the before value. | -7.69 |
| Difference (kg)The gap between two values — a quantity, not a rate. | -6 |
| Loss a week (kg)The weight you aim to lose weekly; 0.5–1 kg is sustainable. | 0.46 |
Common mistakes
Unintentional loss above 5% in six months, or 10% in a year, is treated as a signal worth investigating.
Glossary
- Weight before (kg)
- Your weight when the comparison starts.
- Weight now (kg)
- Today’s weight; measure at the same time and dress for comparison.
- Months
- The period counted in months; a yearly rate gets divided by twelve.
- Change
- How far it moved, measured against the before value.
- Difference
- The gap between two values — a quantity, not a rate.
- Loss a week
- The weight you aim to lose weekly; 0.5–1 kg is sustainable.
Frequently asked questions
Q. How is Weight Change Percentage calculated?
Change = (Weight now (kg) − Weight before (kg)) ÷ Weight before (kg) × 100 — Divide the difference by the earlier weight. The percentage matters more than the kilograms: 3 kg off a 50 kg frame is not the same event as 3 kg off 100 kg.
Q. Can you walk through an example?
With Weight before (kg) 78kg, Weight now (kg) 72kg, Months 3mo, the answer is Change -7.69%.
Q. What do I need to enter?
Enter Weight before (kg), Weight now (kg), Months. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Weight before (kg) (kg) moves the answer to Weight before (kg) (kg) 39 → Change (%) 84.62 and Weight before (kg) (kg) 156 → Change (%) -53.85. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
Unintentional loss above 5% in six months, or 10% in a year, is treated as a signal worth investigating.
Related calculators
These calculators help you understand health figures; they do not replace diagnosis or prescription. See a clinician if you have symptoms.