Online Tool Store
Weight Loss Percentage Calculator
Calculate body-weight percentage lost, progress toward a goal, weekly rate, projected date, and personalized 5% and 10% milestones.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Of your starting body weight
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The 5% and 10% marks
Scale weight moves for reasons that have nothing to do with fat: a full gut, salt, glycogen and hydration swing most people by one to two kilos across a day, and more across a week. A single reading is noise — the trend over several weeks is the signal. This is arithmetic on numbers you typed, not medical advice, and if you are losing weight without meaning to, that is a conversation for a doctor rather than a calculator.
How to use it
- Enter your starting and current weight in kilograms or pounds.
- Add a goal weight to see progress towards it as well.
- Add the two dates to get a weekly rate and a projected date.
- Read the 5% and 10% markers — those are the ones that matter clinically.
The denominator is the whole question
Percentage of body weight lost is measured against where you started, not against where you are now. Both divisions are easy to type and only one is right:
92 kg → 84.5 kg, so 7.5 kg lost
correct 7.5 / 92 = 8.15%
wrong 7.5 / 84.5 = 8.88% ← 9% too high
The gap widens the further you go, and at the extreme the wrong formula stops making sense altogether: someone who halves their body weight has lost 50% of it, but dividing by the current weight gives 100% — which would mean they had lost all of it. If a calculator disagrees with this one, check which weight it divided by.
Two percentages, two questions
start 92 · now 84.5 · goal 78
of body weight 7.5 / 92 = 8.15% how much of you has gone
towards the goal 7.5 / 14 = 53.6% how far along the plan you are
Both are true at the same moment and they will almost never match. The first is the number that matters for health outcomes; the second is the one that matters for morale. Showing them separately, with the division written out, is the point of having them side by side.
Why 5% and 10%, rather than a round number
Clinical guidance is framed in percentages of starting body weight because the same absolute loss means very different things at different sizes. Five kilos is 5.4% of 92 kg and 8.3% of 60 kg. The 5% mark is where blood pressure, glucose handling and lipids typically begin to improve; 10% is where the benefit is firmly established.
from 92 kg 5% = 4.60 kg 10% = 9.20 kg
from 70 kg 5% = 3.50 kg 10% = 7.00 kg
That is why the milestone bar is scaled to your own starting weight rather than to a fixed number of kilos. It also means the first meaningful target is usually closer than people assume.
What the scale is actually telling you
Body weight is a noisy measurement of body fat. Gut contents, salt, hydration and glycogen — which carries roughly three grams of water per gram stored — move most people by one to two kilos across a single day, which is comfortably larger than a good week's fat loss. That is why the first fortnight of any change looks dramatic and then appears to stall: the early drop is largely water leaving with glycogen, and the plateau is fat loss becoming visible against a noisy baseline.
The practical consequence is to weigh under the same conditions, take the trend across weeks rather than any single reading, and treat the projected date here as arithmetic rather than a forecast — it assumes a steady rate, and weight loss is not steady.
FAQ
What is the formula?
Weight lost divided by your starting weight, times 100. Going from 92 kg to 84.5 kg is 7.5 ÷ 92 = 8.15%. The starting weight is the denominator — that is the part people get wrong.
Why does another calculator give me a bigger number?
Because it probably divided by your current weight instead. On the same figures that gives 7.5 ÷ 84.5 = 8.88% — about 9% higher than the truth. The error grows as you lose more: halving your body weight is 50% lost by the correct formula and a nonsensical 100% by the wrong one.
Why are 5% and 10% singled out?
Because those are the thresholds clinical guidance uses. Losing 5% of starting body weight is where blood pressure, blood sugar and lipid markers typically start to shift, and 10% is where the effect is well established. They are much more meaningful targets than a round number on the scale, and they scale with your own starting point.
What is the difference between the two percentages shown?
Percentage of body weight lost measures against where you started. Progress towards the goal measures against the whole distance you set out to cover. From 92 kg to 84.5 kg with an 78 kg goal, those are 8.15% and 53.6% — both correct, answering different questions. Mixing them up is how people end up either discouraged or over-confident.
How fast should I be losing?
Around 0.45 to 0.9 kg — 1 to 2 lb — a week is the range usually described as sustainable. The first fortnight often looks much faster because glycogen carries water with it, so early numbers flatter you. The tool flags a sustained rate above that range rather than silently congratulating it.
Why has the scale not moved when I have been careful?
Because scale weight is not the same measurement day to day. Gut contents, salt, glycogen and hydration move most people by one to two kilos within a single day. A week of no change is entirely normal and says very little; four weeks of no change says something. Weigh under the same conditions and read the trend, not the reading.
How we compare
| Feature | Online Tool Store | Other percentage calculators | Weight-tracking apps |
|---|---|---|---|
| Shows the division it used | ✓ | ✗ | ✗ |
| Separates body-weight % from goal progress | ✓ | ✗ | Usually goal only |
| 5% and 10% markers scaled to you | ✓ | ✗ | Sometimes |
| Flags an unsustainable rate | ✓ | ✗ | Varies |
| No account, no data collected | ✓ | Varies | ✗ |
| Keeps a history and charts the trend | ✗ | ✗ | ✓ |
| Body composition, not just weight | ✗ | ✗ | With a smart scale |
One honest calculation with the arithmetic on show, the two percentages kept apart, and the clinically meaningful marks pointed out. It keeps no history, so if you want a trend line over months an app that stores your readings is the right tool — and because scale weight is noisy, that trend is the thing actually worth watching.