Weight Loss Percentage Calculator

How to use this weight loss percentage calculator

Two weights are enough to get a number. The first question and the optional boxes each change what the number is compared against, which is the part that matters.

1. Answer the intent question honestly. It is not a formality and it is not there for tone. Intended loss gets read against treatment milestones, where bigger is the goal. Loss you did not intend gets read against thresholds for when unexplained weight loss needs investigating, and those sit far lower. The same eight percent can be a result worth being pleased about or a reason to book an appointment.
2. Enter both weights in the same units. Pounds or kilograms, your choice. Switching the unit converts what you already typed rather than just changing the label, so a 200 lb start cannot quietly become a 200 kg one.
3. Read the milestone weights, not just the percentage. The row under your result prints the weight that would be a 5, 10, 15 and 20 percent loss for you, marks the ones you have passed, and tells you how far the next one is. That is the number you can actually aim at, because you can see it on a scale without doing any arithmetic.
4. Add the dates if you have them. They unlock how fast this is going in pounds per week, checked against the rate health authorities describe as sustainable. If the loss was unintended, the dates are what decide which published threshold applies, so they matter more than the total.
5. Add your height for the clinical framing. It gives your BMI at both weights and the percentage of excess weight lost, which is the figure bariatric teams have traditionally reported. The PDF fits one page with your inputs, your milestones and the sources, which makes it something you can hand to a clinician.

Why this tool is different from other weight loss percentage calculators

Dividing one number by another is not hard, and every page ranking for this term does it correctly. Then they all stop. Here is what happens instead:

• It asks whether you meant to lose it. No other calculator on page one does, and it is the single most important thing about the number. Unintended weight loss has published, time-graded thresholds behind it, and this tool applies them: roughly 2 percent in a week, 5 percent in a month, 7.5 percent in three months or 10 percent in six is where the literature says stop calculating and get seen.
• It answers the question people actually type. Google’s own related questions for this term include “how do I calculate a 10 percent weight loss”, and a competitor ranks on page one for nothing more than “5 percent weight loss calculator”. Both are asking for a weight, not a ratio. This tool prints four of them.
• Every band is a named trial or guideline. Three percent is where the guideline evidence says triglycerides and blood glucose start moving. Seven percent is what the Diabetes Prevention Program used. Ten to fifteen percent is the range where a majority of participants in the DiRECT trial saw type 2 diabetes go into remission. Fifteen and twenty percent are roughly what semaglutide and tirzepatide reached in their trials. The sources are listed below and every boundary is checked by a fixture file on each build.
• It checks the speed, not only the total. Pounds per week against the 1 to 2 lb figure health authorities describe as sustainable, with a plain explanation of why faster is usually water at first and why it stops being harmless if it holds.
• It shows both percentages bariatric teams use. Total weight loss and percentage of excess weight lost, side by side, with a note on why the professional society now asks for the first one.
• No login, no newsletter wall, no ads, and it embeds free. Nothing on this page interrupts you before the result.

How it works (the math)

The percentage is one subtraction and one division:

Weight loss % = (starting weight − current weight) ÷ starting weight × 100

Starting at 200 lb and now at 180 lb is 20 lb lost, and 20 divided by 200 is 0.10, so 10 percent. The units cancel, which is why the same arithmetic in kilograms gives the identical answer: 90 kg down to 81 kg is also 10 percent. Both of those are asserted as test fixtures that run on every build of this site.

Running it backwards gives the milestone weights:

Target weight for N% = starting weight × (1 − N ÷ 100)

From 200 lb, a 5 percent loss is 190 lb, 10 percent is 180 lb, 15 percent is 170 lb and 20 percent is 160 lb.

What the bands are built from. The clinical interest in percentage of body weight rather than pounds is that it scales. Ten pounds off a 300 lb frame is a different event from ten pounds off a 130 lb one, and the trials report percentages for exactly that reason.

• 3 to 5 percent: the smallest loss with a documented payoff. Triglycerides, blood glucose and HbA1c improve.
• 5 to 10 percent: the target the major guideline sets for six months. Blood pressure and lipids improve alongside glycaemic control.
• 10 to 15 percent: obstructive sleep apnoea and fatty liver, and the range in which type 2 diabetes remission became common in DiRECT.
• 15 percent and above: what the GLP-1 receptor agonists reached in trials, and long the territory of bariatric surgery.

Percentage of excess weight lost is a different denominator, not a different idea. Excess weight is your starting weight minus the weight that would put you at a BMI of 25, and the percentage is how much of that gap has closed. It flatters a small starting excess: 15 lb is 60 percent of a 25 lb excess and 17 percent of a 90 lb one. That is the reason the American Society for Metabolic and Bariatric Surgery’s standardised reporting statement asks for total weight loss instead, and why the large number on this page is the total.

What the percentage cannot tell you. It is scale weight, so it counts fat, muscle and water without distinguishing them. Body weight swings one to two percent inside a single day on fluid alone, which is why a change under about two percent is not yet distinguishable from noise, and why a scale that does not drift matters more than any decimal place here. If you want to know what you lost rather than how much, the lean body mass calculator is the next measure along.

Worked examples

200 lb down to 180 lb, over five months, on purpose

Twenty pounds is 10 percent, which clears the 5 percent milestone at 190 lb and lands exactly on the 10 percent one at 180 lb. Over roughly 20 weeks that is a pound a week, at the calm end of the sustainable range. This is the band where blood pressure, lipids and fasting glucose have all been shown to improve together, so it is worth finding out whether yours did. A home blood pressure monitor answers half of that question for the price of a takeaway.

250 lb down to 200 lb at 5 foot 10, on purpose

Fifty pounds is 20 percent, the top milestone, and BMI falls from about 35.9 to 28.7. Excess weight against a BMI of 25 was about 76 lb, so roughly 66 percent of it is gone. At this size of loss the composition question stops being academic: some of it is always muscle, and the body-composition substudy of the semaglutide trial found a substantial share of total loss was lean tissue. Enough protein and resistance training two or three times a week is what changes that split, which is why the tool starts recommending protein and resistance bands rather than anything to do with eating less, once you pass 10 percent.

200 lb down to 188 lb in a month, not on purpose

Six percent, and the picture inverts. On the intended reading this is a good month. On the unintended reading it is above the 5 percent threshold that the literature treats as significant for a one-month window, and the same 12 lb spread over three months would not have been. Unexplained weight loss is a general-purpose signal rather than a specific one. Thyroid disease, diabetes, coeliac disease, inflammatory bowel disease, depression, a new medication and infection can all present this way, and so can nothing at all. The tool says book an appointment and declines to recommend you anything, because a red flag is not a shopping moment.

Frequently asked questions

How do you calculate weight loss percentage?

Subtract your current weight from your starting weight, divide the result by your starting weight, and multiply by 100. Starting at 200 lb and now at 180 lb: 200 minus 180 is 20, 20 divided by 200 is 0.10, times 100 is 10 percent. It works identically in kilograms, stones or any other unit, as long as both weights use the same one, because the units cancel in the division. That is also why you never need to convert anything to answer this particular question.

How do I calculate a 10 percent weight loss?

Multiply your starting weight by 0.9. From 200 lb that is 180 lb, from 250 lb it is 225 lb, from 90 kg it is 81 kg. For 5 percent multiply by 0.95, for 15 percent by 0.85, for 20 percent by 0.8. The calculator above prints all four for your own starting weight and marks the ones you have already passed. Ten percent is the threshold worth knowing because it is where sleep apnoea, fatty liver disease and, in the DiRECT trial, remission of type 2 diabetes start appearing in the outcomes.

Is losing 20 percent of body weight noticeable?

Yes, unmistakably, and usually well before that. Visible change tends to start somewhere around 5 percent and is generally obvious to other people by 10, though where it shows first varies by person and is not something you get to choose. Twenty percent is a different category: it is the range bariatric surgery and the newer obesity drugs reach, it usually means a change of clothing size more than once, and it is enough that loose skin and lean tissue loss become real considerations rather than theoretical ones. That last point is why protein intake and resistance training move from optional to central at this level.

How much unexplained weight loss is a red flag?

The usual rule of thumb is 5 percent of body weight over 6 to 12 months without trying. Over shorter windows the bar is proportionally tighter: roughly 1 to 2 percent in a week, 5 percent in a month, 7.5 percent in three months and 10 percent in six are the long-standing criteria for calling a loss clinically significant. The calculator applies whichever window fits your dates. Two things make this worth taking seriously even when you feel fine. Unexplained loss is associated with a long list of conditions rather than one, and in older adults it predicts outcomes independently of whatever is causing it. If you are over 65 and losing weight you did not intend, that is a conversation to have sooner rather than at the next routine appointment.

Can I use this for a newborn’s weight loss?

No, and it is worth knowing why rather than just being told not to. The arithmetic is the same, but newborn weight loss is not assessed against a single percentage of birth weight. It is read against hour-by-hour nomograms that account for how old the baby is in hours and whether feeding is by breast or formula, because a 7 percent loss at 24 hours and a 7 percent loss at 72 hours are different situations entirely. Around 7 percent is commonly cited as the point to look closely at feeding and 10 percent as the point for evaluation, but the percentage alone is not the instrument. Ask your midwife, health visitor or paediatrician, who will plot it properly.

Related tools

• TDEE Calculator: daily energy expenditure, the number that moves the one on this page.
• Ideal Body Weight Calculator: four published formulas, with the same show-the-disagreement approach.
• Lean Body Mass Calculator: fat-free mass, for the composition question a percentage cannot answer.
• Waist to Height Ratio Calculator: where the weight sits, which tracks risk more closely than how much of it there is.
• Protein Intake Calculator: how much protein it takes to hold onto muscle while the scale moves.
• Browse all free tools by Dr. Taylor →

Dr. Taylor’s recommendations

The calculator picks from these based on your result and whether the loss was intended. All of them, in one place:

• Best Bathroom Scales. Every number on this page is only as good as the two weights you fed it. A scale drifting two pounds can invent a milestone you have not reached or erase one you have.
• Best Fiber Supplements. The least punishing lever on the first few percent, because it improves how full you feel without asking you to eat less food.
• Best Protein Powders. Past about 10 percent, how much of the loss is muscle stops being an academic question. Protein intake is half of what decides it.
• Best Resistance Bands. The other half. Losing strength alongside weight is the outcome worth avoiding, particularly past fifty.
• Best Blood Pressure Monitors. Blood pressure is one of the things the 5 to 10 percent band is defined by improving, and it is measurable at home.
• Best Glucose Monitors. Fasting glucose and HbA1c are the other two. This is how you find out whether the percentage moved anything.
• Best Electrolyte Powders. Fast early loss is largely water, and the headaches and cramps that come with it are usually sodium and potassium leaving alongside it.

Sources & methodology

• Jensen MD, Ryan DH, Apovian CM, et al. 2013 AHA/ACC/TOS Guideline for the Management of Overweight and Obesity in Adults. Circulation 2014;129(25 Suppl 2):S102–S138. The source of the 3 to 5 percent and 5 to 10 percent bands.
• Diabetes Prevention Program Research Group. Reduction in the Incidence of Type 2 Diabetes with Lifestyle Intervention or Metformin. N Engl J Med 2002;346:393–403. The 7 percent target and the 58 percent risk reduction.
• Lean MEJ, Leslie WS, Barnes AC, et al. Primary care-led weight management for remission of type 2 diabetes (DiRECT). Lancet 2018;391:541–551. The remission figures behind the 10 to 15 percent band.
• Wilding JPH, Batterham RL, Calanna S, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med 2021;384:989–1002, and its body-composition substudy.
• Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med 2022;387:205–216.
• CDC, Losing Weight: the 1 to 2 lb per week figure this tool checks the rate against.
• Gaddey HL, Holder KK. Unintentional Weight Loss in Older Adults. Am Fam Physician 2014;89(9):718–722, which reproduces the Blackburn time-window criteria (Blackburn GL et al., JPEN 1977) used for the unintended reading.
• Brethauer SA, Kim J, el Chaar M, et al. Standardized outcomes reporting in metabolic and bariatric surgery. Surg Obes Relat Dis 2015;11:489–506. The excess-weight-loss definition, and the reason total weight loss is now the preferred report.

Every band boundary, unit conversion, rate figure and edge case on this page is checked against a fixture file on each build, including the 200 lb to 180 lb worked case that the other calculators ranking for this term also use. This tool is reviewed annually, and sooner if the guideline bands are revised. About Dr. Taylor · Last reviewed September 25, 2026.

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