Weight Loss Percentage Calculator

A weight loss percentage calculator turns two weigh-ins into one comparable number: the share of your starting body weight you have lost. Going from 220 lb to 202 lb is an 18 lb drop, which works out to 8.18% of the starting weight. That percentage is what the CDC and NIDDK use when they say a 5-10% loss already improves health markers.

This page measures what has already happened. If you want to plan ahead instead, the Weight Loss Calculator builds a calorie target and a dated timeline to a goal weight, the Calorie Deficit Calculator finds the daily deficit for a chosen pace, and the BMI Calculator tells you where your current weight sits on the height-adjusted scale. Use this calculator to score progress you have made; use those to decide what to do next.

The percent weight loss formula

The calculation is a simple ratio. Because both weights are in the same unit, the unit cancels and the answer is the same in pounds or kilograms:

Two follow-on numbers come from the same inputs. Weight lost is just the difference between the two readings. The weekly rate divides that difference by the number of weeks between weigh-ins, and dividing the percentage by the weeks gives the rate as a percent per week. The milestone targets run the formula backwards: the weight at a 10% loss is the starting weight × 0.90.

Worked example: 220 lb to 202 lb in 12 weeks

Here is every step for someone who weighed 220 lb on day one of a program and 202 lb twelve weeks later:

In metric the same person went from 99.8 kg to 91.6 kg, an 8.2 kg loss, and the percentage is unchanged at 8.18%. At the current 1.5 lb per week pace, the remaining 4 lb to the 10% milestone takes a little under three more weeks.

Percent lost by starting weight

The same number of pounds means a very different percentage depending on where you started. The table runs the formula for four common amounts lost:

Twenty pounds is a 13.3% loss at 150 lb but only 6.7% at 300 lb. This is exactly why percentages, not pounds, are the fair way to compare two people or to judge whether you have hit a health-relevant threshold.

Weight at 5%, 10% and 15% loss

Federal guidance frames the first health goal as a 5-10% loss. This table shows what that means on the scale for a range of starting weights, computed as starting weight × (1 − percent):

Notice that the first health milestone is often smaller than people expect: a 250 lb adult reaches 5% at 237.5 lb, a loss of 12.5 lb, well before any number that looks like a "goal weight."

How fast is a healthy percentage per week?

The CDC describes gradual, steady loss of about 1 to 2 pounds per week as the pace people are most likely to keep off. Expressed as a percentage it depends on your size: at 200 lb, 1 lb per week is 0.5% per week and 2 lb per week is 1.0% per week. The table below shows what 12 weeks at each pace adds up to, and how many pounds a "1% per week" rule of thumb equals at each starting weight:

A 150 lb person losing 2 lb per week is shedding 1.3% of their body weight weekly, a much more aggressive pace than the same 2 lb for a 300 lb person (0.67% per week). If the calculator shows your weekly percentage climbing above about 1%, that is a signal to check that you are not under-eating, especially at lower body weights.

How to use this weight loss percentage calculator

1. Pick your units. US units (pounds) are the default; switch to metric for kilograms. The percentage is identical either way.
2. Enter your starting weight. Use the weigh-in from the first day of the period you are measuring, ideally taken under the same conditions as today's reading (same scale, same time of day, before eating).
3. Enter your current weight. If it is above the starting weight the calculator flips to "gained" instead of "lost" so nothing breaks.
4. Add the weeks between weigh-ins (optional). This unlocks the weekly rate in both pounds and percent so you can compare your pace against the 1-2 lb per week guidance. The quick buttons cover 4, 8, 12, 26 and 52 weeks.
5. Read the result. The big number is the percent of starting weight lost. Below it you get the absolute loss (with the other unit in brackets), the weekly rate, the three milestone cards and a ladder of target weights from 1% to 20%.

Who this calculator is for

• Anyone on a weight loss program who wants to know whether they have crossed the 5% or 10% line that federal health agencies call clinically meaningful.
• Workplace and family challenges that rank participants by percentage so that a 150 lb and a 300 lb entrant compete fairly.
• Patients tracking a doctor's target. Clinicians frequently set weight goals as a percentage ("aim for 7% over six months") rather than as a fixed number of pounds.
• Coaches and trainers reporting client results in a size-neutral way.
• Athletes making weight who need to know what a 3% or 5% cut means on the scale from their walk-around weight.

Why percentages beat pounds in a challenge

Consider three people in the same 8-week contest. Person A starts at 250 lb and finishes at 235 lb: 15 lb lost, 6.00%. Person B starts at 160 lb and finishes at 150 lb: only 10 lb lost, but 6.25%. Person C goes from 195 lb to 181 lb: 14 lb, 7.18%. Ranked by pounds the order is A, C, B. Ranked by percentage it is C, B, A. Because a heavier body burns more calories doing the same activity and can carry a larger calorie deficit comfortably, the percentage ranking is the one most challenge organizers and the medical literature use.

Key terms

• Starting weight: the reference weigh-in that every percentage is measured against. It stays fixed for the whole program, even after you pass milestones.
• Percent of body weight lost: the loss divided by the starting weight. A 10% loss at 220 lb means the scale reads 198 lb.
• Weekly rate: total loss divided by elapsed weeks. Shown here both as lb (or kg) per week and as percent per week.
• Milestone: a percentage threshold with a health meaning attached. The CDC and NIDDK highlight 5% and 10%; this tool adds 15% as a stretch marker.
• Target weight at X%: starting weight × (1 − X ÷ 100). This is what the ladder table lists for every whole percent from 1 to 20.

What changes the result

• The starting weight you choose. Measuring from a years-old peak instead of the first day of your current program inflates the percentage and hides recent plateaus.
• Weigh-in conditions. Water, sodium, glycogen and meal timing can swing the scale by 2-5 lb within a day. At 150 lb that noise alone is worth up to 3.3 percentage points, so compare morning-to-morning readings.
• Time window. The percentage does not care how long it took, but the weekly rate does. Twelve weeks versus twenty weeks for the same 18 lb is 1.5 lb/week versus 0.9 lb/week.
• Body composition. Two people can lose the same 8% and have very different fat-versus-muscle results. Resistance training tends to lower the scale number more slowly while improving how you look and function.
• Rounding. Scales that read in whole pounds can hide up to a half-pound; at 100 kg a 0.5 kg reading error changes the percentage by 0.5 points.

Tips for meaningful tracking

• Weigh in at the same time each week, first thing in the morning after using the bathroom and before breakfast.
• Record the starting weight on day one and never revise it; revising it resets your percentage and breaks comparability.
• Judge trends over 2-4 weeks rather than single readings. A rolling weekly average smooths water swings.
• Pair the percentage with a waist measurement or the Body Fat Calculator so muscle gain does not read as failure.
• Celebrate 5% and 10%. Both are milestones that federal agencies associate with better blood pressure, blood sugar and cholesterol, regardless of the "ideal" number on a chart.

Limitations

• The formula compares two scale readings only. It does not separate fat, muscle, bone or water, and it cannot assess health on its own.
• It makes no forecast. The weekly rate is the historical average between your two weigh-ins, not a prediction that the same pace will continue; weight loss usually slows as you get lighter.
• The 5-10% milestones are population-level guidance for adults with overweight or obesity. They are not targets for people already at a healthy weight, for children, or during pregnancy.
• A very fast percentage per week (above roughly 1% for most adults) can indicate muscle loss or an unsafe deficit. This tool reports the rate; it does not judge whether it is safe for you.
• This is an educational calculator, not medical advice. Talk to a doctor or registered dietitian before starting or changing a weight loss program.

Related calculators and when to use which

This page answers "how much of my body weight have I lost so far?" Use the Weight Loss Calculator when you want a forward-looking plan with a calorie target and a goal date, the Calorie Deficit Calculator when you already have a pace in mind and need the daily deficit to hit it, the BMI Calculator to see which weight category your current reading falls into, and the Ideal Weight Calculator for a height-based reference range. For the maintenance calories you will need once you reach a milestone, the Maintenance Calorie Calculator picks up where this one leaves off.

Sources

• Centers for Disease Control and Prevention (CDC) - Steps for Losing Weight (gradual loss of 1-2 lb per week; 5-10% of body weight improves health).
• National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) - Treatment for Overweight & Obesity (a 5-10% loss lowers the risk of weight-related health problems).