Weight Loss Percentage Calculator
Percentage of starting weight is how clinical research reports weight loss, and it is a fairer measure than absolute pounds or kilograms — the same ten pounds means something quite different depending on where you started. This calculator gives you the percentage and marks where the 5% and 10% thresholds fall.
Your result
Fill in the fields on the left and your result appears here.
The calculation
Percentage lost is the difference between starting and current weight, divided by the starting weight, times one hundred. Because it is relative to where you began, it is directly comparable between people of different sizes — which is exactly why trials report it this way.
The 5% and 10% markers are not arbitrary. Clinical guidance widely treats a 5% reduction as the point where metabolic benefits become measurable, and 10% as a larger threshold associated with more substantial improvement across several markers.
Track it, don't recalculate it.
Pep AI logs your weight, meals and protein alongside your schedule, so the numbers on this page turn into a trend instead of a one-off. Free on iOS and Android.
Reading the number sensibly
Weight loss is not linear, and a percentage figure calculated from two points on a jagged line inherits all that noise. Water shifts of a few pounds can mask real change for weeks at a time, particularly around changes in carbohydrate intake, salt, training load or menstrual cycle.
The way to get a usable number is to compare like with like: weigh under consistent conditions, and read the trend across weeks rather than any two individual readings. A weekly average is far more informative than a daily figure.
It is also worth remembering that percentage lost says nothing about composition. Two people at the same percentage can have lost very different proportions of fat and lean tissue, and that difference is not visible on a scale.
Frequently asked questions
This calculator is general information for healthy adults, not medical or dietary advice. It applies published population formulas and cannot account for your clinical situation. Where a clinician has set you a target, that target replaces this one.
Built by the Pep AI team.