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Weight loss percentage calculator
How much of your starting weight you have actually lost, which is the only figure that compares across different bodies and different months. It also shows how far through your own goal you are. Nothing leaves your browser.
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Why the percentage is the honest number
Pounds flatter the heavy and punish the light. Ten pounds off a 280 pound frame is 3.6% and will barely show in a mirror; the same ten pounds off 130 is 7.7% and changes how clothes fit. Neither person worked less hard. The percentage is what lets you compare at all.
It is also how the research reports results, which is why the thresholds below are worth knowing rather than inventing your own.
| Lost | What tends to change |
|---|---|
| 3 to 5% | Triglycerides and blood sugar begin to move. Often no visible change yet, which is where most people quit. |
| 5 to 10% | Blood pressure, cholesterol and insulin sensitivity all improve measurably. Clothes change. |
| 10 to 15% | The largest gains in metabolic health. Sleep apnoea and joint pain often ease. |
| Over 15% | Further benefit, and the point at which holding on becomes the harder job than losing. |
Rate matters as much as total. Half to one percent of body weight a week is the band that keeps muscle. Faster, and a growing share of what leaves is lean tissue you will want back.
Measuring it without fooling yourself
Weigh at the same time each morning, after the bathroom, before eating, and use the weekly average rather than any single day. Water swings of a kilo or two are ordinary and have nothing to do with fat. A percentage computed from two bad mornings is a fiction with a decimal point on it.
Is it fat? The scale cannot say. The body fat calculator and a tape will tell you whether the percentage you just computed is the kind you wanted.
Working it out in stone and pounds
The calculator takes pounds, so a scale that reads in stone needs one step first: multiply the stones by 14 and add the pounds. 15 st 7 lb is 15 times 14, plus 7, which is 217 lb. Do the same for today's reading and the percentage comes out exactly as a stone calculator would give it, because a percentage has no unit.
A worked example. From 15 st 7 lb to 14 st 1 lb is 217 lb down to 197 lb, so 20 lb lost, or 1 st 6 lb. Divide 20 by 217 and the answer is 9.2%, just short of the 10% line where the biggest health changes start.
| Starting weight | 5% is | 10% is | 15% is |
|---|---|---|---|
| 12 st | 8 lb | 1 st 3 lb | 1 st 11 lb |
| 14 st | 10 lb | 1 st 6 lb | 2 st 1 lb |
| 16 st | 11 lb | 1 st 8 lb | 2 st 6 lb |
| 18 st | 13 lb | 1 st 11 lb | 2 st 10 lb |
| 20 st | 1 st | 2 st | 3 st |
The usual slip is treating stone as decimal. 14 st 7 lb is 14.5 stone, not 14.7, because there are 14 pounds in a stone rather than 10. Typing 14.7 into a stone field quietly adds 3 lb to your starting weight and flatters the result.
The weekly pace in the same units: at 16 stone, half to one percent a week is roughly 1 to 2 lb. At 12 stone it is closer to 1 to 1.5 lb.
How your number compares with the trials
Most people carry a headline figure from the weight loss injections around with them, and measure themselves against it. Here is what the large trials actually reported, each as a share of starting weight, which is the same figure the calculator gives you.
| Trial | What people did | Average lost |
|---|---|---|
| Look AHEAD, 1 year | Intensive diet and activity programme, with coaching | 8.6%, against 0.7% for the comparison group |
| STEP 1, 68 weeks | Semaglutide 2.4 mg weekly plus lifestyle advice | 14.9%, against 2.4% on placebo |
| SURMOUNT 1, 72 weeks | Tirzepatide 15 mg weekly plus lifestyle advice | 20.9%, against 3.1% on placebo |
Two things follow. If food and movement alone have taken you to 8 or 9% in a year, you have matched one of the largest supervised lifestyle programmes ever run, which had group sessions and meal replacements behind it. That is not falling short of an injection; it is a different comparison. And the 20% bar on the calculator sits at roughly what the highest tirzepatide dose averaged, so crossing it on your own is rare.
Sources
- Benefits of modest weight loss in improving cardiovascular risk factors in overweight and obese individuals with type 2 diabetes, Diabetes Care, 2011
- Weight loss and improvement in comorbidity: differences at 5%, 10%, 15%, and over, Current Obesity Reports, 2017
- Treatment for overweight and obesity, National Institute of Diabetes and Digestive and Kidney Diseases, 2023
- Overweight and obesity management (NG246), National Institute for Health and Care Excellence, 2025
- Reduction in weight and cardiovascular disease risk factors in individuals with type 2 diabetes: one year results of the Look AHEAD trial, Diabetes Care, 2007
- Once weekly semaglutide in adults with overweight or obesity (STEP 1), New England Journal of Medicine, 2021
- Tirzepatide once weekly for the treatment of obesity (SURMOUNT 1), New England Journal of Medicine, 2022
How this was made
Written by Abdullah Javaid, founder of Calfit, drafted with AI assistance and edited by hand. The percentage is the weight you have lost divided by your starting weight, and progress to goal is the weight lost divided by the total you set out to lose. The threshold table summarises the clinical studies listed above, and the trial figures are the headline results from each trial's own published abstract. The stone table is plain arithmetic at 14 lb to the stone.
