How to Calculate Weight Loss Percentage: Formula and Examples

The weight loss percentage formula, with a worked example

Percent lost = (starting weight minus current weight) divided by starting weight, times 100. Worked example: 200 lb down to 180 lb is 20 lb lost, 20 divided by 200 is 0.10, and times 100 that is 10 percent.

Percent is useful because it scales to your body. Ten pounds lost is 3.3 percent of a 300 lb starting weight and 6.7 percent of a 150 lb starting weight. Same ten pounds, very different share of the body it came from. That is why clinical guidance and trials report percentages instead of raw pounds.

Two more to check your work. From 150 lb to 125 lb is 25 lb lost; 25 divided by 150 is 0.167, or 16.7 percent. From 90 kg to 82 kg is 8 kg lost; 8 divided by 90 is 0.089, or 8.9 percent.

Some calculators run it as ((current divided by starting) minus 1) times 100. For 200 lb to 180 lb that gives minus 10. It is the same calculation with the sign flipped, not a second formula. A negative number means weight went down.

Step by step: how to calculate your own percentage in pounds or kilograms

• Write down your starting weight.
• Write down your current weight in the same unit. Never mix kilograms and pounds in one calculation. Convert first, since 1 kg is about 2.2 lb.
• Subtract current weight from starting weight to get pounds (or kilograms) lost.
• Divide that number by your starting weight.
• Multiply by 100. That is your percent of starting body weight lost.

In kilograms the steps are identical: 90 kg minus 82 kg is 8, 8 divided by 90 is 0.089, times 100 is 8.9 percent. The unit cancels out, which is why the answer is the same percentage whether you work in pounds or kilograms, as long as both numbers use one unit.

Percentage of body weight is a different measure from BMI, which uses height and weight at a single point in time. If you are checking program eligibility rather than progress, see GLP-1 BMI requirements.

What weight equals 5, 10, 15 or 20 percent of your starting weight

To go the other direction, use target weight = starting weight times (1 minus percent divided by 100). For 200 lb at 10 percent: 200 times (1 minus 0.10) is 200 times 0.90, or 180 lb.

On what those bands mean clinically, the 2013 AHA/ACC/TOS guideline for adults with overweight or obesity and cardiovascular risk factors states that lifestyle changes producing even modest, sustained weight loss of 3%, 5% produce clinically meaningful health benefits, and greater weight losses produce greater benefits. It describes sustained weight loss of 3%, 5% as likely to result in clinically meaningful reductions in triglycerides, blood glucose, hemoglobin A1c, and the risk of developing type 2 diabetes. That is guidance written for a population, not a prediction for one person.

Which starting weight to use, and why weekly averages help

Use your weight on the day you start as the starting weight. If you are beginning a medicine, that means the weight you recorded before the first dose, not a weight from last year and not the highest number you have ever seen.

Weigh at the same time of day, on the same scale, under the same conditions. Day-to-day readings move for reasons that have nothing to do with fat loss, so averaging a week of weigh-ins and comparing week-average to week-average smooths the noise out of your percentage.

Clinical guidance is built the same way. The 2013 AHA/ACC/TOS guideline recommends as an initial goal the loss of 5%, 10% of baseline weight within 6 months, which shows that loss is measured against a defined baseline. That is how the guideline frames a goal for clinicians, not a target you should set for yourself. Your own target belongs in a conversation with a licensed provider.

Total body weight loss vs excess weight loss

These two numbers use the same pounds lost but different denominators.

• Total body weight loss = pounds lost divided by starting weight, times 100.
• Excess weight loss = pounds lost divided by (starting weight minus a reference weight the clinic chooses), times 100.

Example: 200 lb to 180 lb is 20 lb lost. Against a 150 lb reference weight, excess weight is 50 lb, so 20 divided by 50 is 0.40, or 40 percent of excess weight. The same 20 lb is 10 percent of total body weight. Four times the number, same scale reading.

A clinic, a program or a study can mean either one, and the reference weight is a choice someone made. If you see a percentage quoted without a definition, ask which denominator it used.

How to work out your weekly or monthly percentage, and do it in a spreadsheet

Rate is just arithmetic: percent lost divided by weeks (or months) elapsed. If you are down 10 percent over 20 weeks, that is 10 divided by 20, or 0.5 percent a week. The same 10 percent over 5 months is 2 percent a month. What rate is appropriate for you is a question for your clinician, not a formula.

Spreadsheet formulas

Put your starting weight in cell B1 and your current weight in cell B2. In another cell, enter =(B1-B2)/B1 and format that cell as a percentage. To get a target weight, put the percent as a decimal in C1 (0.1 for 10 percent) and enter =B1*(1-C1). Both formulas work the same way in Excel and in Google Sheets.

If you track against dose steps, the step tables in the tirzepatide dosage chart and the semaglutide dosage chart give you dates to line your weekly averages up against.

How GLP-1 medicine trials report weight loss as a percentage

Trials of the approved injections report weight change as a mean percent change in body weight from baseline at a set week. It is the same formula you just used, applied to every participant and then averaged.

In SURMOUNT-1, which studied tirzepatide once weekly, the mean percentage change in weight at week 72 was -15.0% with 5-mg weekly doses of tirzepatide, -19.5% with 10-mg doses, and -20.9% with 15-mg doses and -3.1% with placebo.

In STEP 1, which studied the semaglutide 2.4 mg once-weekly injection, the mean change in body weight from baseline to week 68 was -14.9% in the semaglutide group as compared with -2.4% with placebo.

Those are results for the approved injections studied in those trials, and they are averages across participants under trial conditions. They are not a prediction of your number. Your own percentage uses the identical formula but describes one person over whatever period you measured. For a side-by-side of the two medicines, see tirzepatide vs semaglutide.

When weight loss is a reason to call a clinician

Not every percentage is good news. MedlinePlus defines unintentional weight loss as loss of 10 pounds (4.5 kilograms) or 5% of your normal body weight over 6 to 12 months or less without knowing the reason, and says to contact a provider if you have lost more than 10 pounds (4.5 kilograms) or 5% of your normal body weight over 6 to 12 months or less and you do not know the reason.

If your percentage is moving and you cannot explain why, or if weight is dropping faster than you expected on any treatment, talk with a licensed clinician. Bring your log: dates, weights and your calculated percentage make the conversation faster.

Belle offers compounded tirzepatide and compounded semaglutide through a licensed provider who reviews your history and decides whether treatment is appropriate. Compounded medications are not FDA approved finished products. A licensed provider determines eligibility.

Key points

• Percent lost = (starting weight minus current weight) divided by starting weight, times 100. Going from 200 lb to 180 lb is 20 lb lost, and 20 divided by 200 is 0.10, or 10 percent.
• Use the same unit for both weights. Convert first if needed, since 1 kg is about 2.2 lb.
• To find a target weight, flip the formula: target = starting weight times (1 minus percent divided by 100).
• Total body weight loss and excess weight loss use different denominators and give very different numbers from the same pounds lost, so ask which one a clinic or study means.
• Losing more than 10 pounds (4.5 kilograms) or 5% of your normal body weight over 6 to 12 months or less without knowing the reason is a reason to contact a provider.

Q: How do I calculate percent body weight loss?

A: Subtract your current weight from your starting weight, divide by your starting weight, then multiply by 100. Example: 200 lb to 180 lb is 20 lb lost, 20 divided by 200 is 0.10, times 100 is 10 percent.

Q: Is weight loss percentage the same as excess weight loss?

A: No. Total body weight loss divides pounds lost by your starting weight. Excess weight loss divides pounds lost by your starting weight minus a reference weight the clinic chooses. Going 200 lb to 180 lb with a 150 lb reference is 20 divided by 50, or 40 percent of excess weight, but only 10 percent of total body weight. Ask which one a program means.

Q: Which starting weight should I use?

A: Use your weight on the day you start, and if you are beginning a medicine, use the weight you recorded before treatment. Weigh at the same time of day on the same scale, and average a week of weigh-ins to smooth out day-to-day swings.

Q: What weight is 5 or 10 percent of my starting weight?

A: Use target weight = starting weight times (1 minus percent divided by 100). At 200 lb, 5 percent down is 190 lb and 10 percent down is 180 lb. At 250 lb, 5 percent down is 237.5 lb and 10 percent down is 225 lb. The table above covers 150, 180, 200, 220, 250 and 300 lb at 5, 10, 15 and 20 percent.

Q: How do I calculate weight loss percentage in Excel or Google Sheets?

A: Put your starting weight in B1 and your current weight in B2, then enter =(B1-B2)/B1 in another cell and format it as a percentage. For a target weight, put the percent as a decimal in C1 and enter =B1*(1-C1). Both work in Excel and Google Sheets.

Q: Can I use kilograms and pounds together?

A: No. Use the same unit for both weights and convert first if needed, since 1 kg is about 2.2 lb. Worked in one unit, the answer is the same percentage either way: 90 kg to 82 kg is 8 divided by 90, or 8.9 percent.

Q: How do I work out my weekly percentage?

A: Divide your percent lost by the number of weeks elapsed. Ten percent over 20 weeks is 0.5 percent a week. For months, divide by months instead. What rate is right for you is a question for your clinician.

Q: How do GLP-1 trials report weight loss?

A: As a mean percent change in body weight from baseline at a set week. In SURMOUNT-1, mean percentage change in weight at week 72 was -15.0% with 5-mg weekly doses of tirzepatide, -19.5% with 10-mg doses, -20.9% with 15-mg doses and -3.1% with placebo. In STEP 1, mean change from baseline to week 68 was -14.9% with semaglutide versus -2.4% with placebo. Those are averages across participants in trials of the approved injections, not a prediction for any individual.