Body Percent Weight Loss Calculator
Body percent weight loss calculator works out Answer for the selected comparison and What the answer is from Initial / accepted / first value and Final / measured / second value. The default figures on this page give answer for the selected comparison of -50 %; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
3 steps
- Weight lost = 50 - 75 = -25
- Divide by the starting weight: -25 / 50 = -0.5
- Multiply by 100: -50% of the starting body weight
Its 11 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
2 sources
What the body percent weight loss calculator calculates
Compares two values and reports the percentage increase or decrease from the first to the second, the symmetric percentage difference between them (which divides by the mean of the two magnitudes, not by the starting value), the percent improvement toward whichever direction is better, and the percent or relative error of a measurement against an accepted value.
How to use this body percent weight loss calculator
Enter Initial / accepted / first value and Final / measured / second value. Answer for the selected comparison updates as you type. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Answer for the selected comparison, What the answer is and In words.
The method follows Wikipedia, "Relative change and difference" — relative change uses |x_reference| in the denominator; percentage difference uses the mean of the magnitudes and OpenStax, Chemistry 2e §1.5 "Measurement Uncertainty, Accuracy, and Precision" — percent error = |experimental - accepted| / accepted x 100.
What you can compare
Change one input at a time to see how it affects Answer for the selected comparison, What the answer is and In words. The inputs you can vary are Initial / accepted / first value and Final / measured / second value.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
How do I calculate my body percentage loss?
Compares two values and reports the percentage increase or decrease from the first to the second, the symmetric percentage difference between them (which divides by the mean of the two magnitudes. Open “How this is worked out” beside the result to see each step for your own figures.
What is the 3-3-3 rule to lose weight?
On the figures this page opens with — initial / accepted / first value 50 and final / measured / second value 75 — the answer for the selected comparison is -50%. No single number fits everyone: change any figure above and the answer updates as you type, with each step of the arithmetic beside it.
Is losing 20% of body weight noticeable?
Compares two values and reports the percentage increase or decrease from the first to the second, the symmetric percentage difference between them (which divides by the mean of the two magnitudes. On the figures this page opens with — initial / accepted / first value 50 and final / measured / second value 75 — the answer for the selected comparison is -50%. Put your own figures in their place and the working updates beside the result.
How to calculate body fat percentage for weight loss?
It needs Initial / accepted / first value and Final / measured / second value. Nothing else is required, and the figures stay in your browser.
What information do I need for the body percent weight loss calculator?
You need Initial / accepted / first value and Final / measured / second value. The page opens with default figures that give answer for the selected comparison of -50 %, so you can see the scale before entering your own.
What does this body percent weight loss calculator show?
It shows Answer for the selected comparison, What the answer is, In words, Percentage change, Percentage increase, Percentage decrease, Absolute change (final - initial) and Percentage difference, with the working and any warnings for your entries.