Weight Loss Percentage Calculator

Track How Much Body Weight You Have Lost

Weight Loss Percentage Formula

Formula

\[ \text{Weight loss (\%)} = \frac{W_0 - W_1}{W_0} \times 100 \]

Where:

\(W_0\) — starting weight, your weight at the beginning of the period
\(W_1\) — current weight, your weight at the latest weigh-in

The formula expresses the weight you have lost as a share of your starting body weight. A positive result means you weigh less than at the start; a negative result means you have gained.

Weight Loss % – Calculation Example

Example: you weighed 85 kg on January 6 and 78.2 kg on March 3 — 56 days, or exactly 8 weeks later.

\[ \text{Loss} = \frac{85 - 78.2}{85} \times 100 = \frac{6.8}{85} \times 100 = 8.0\% \]

Result: you have lost 6.8 kg, which is 8.0% of your starting body weight — an average of 0.85 kg (1.0% of body weight) per week. With a goal weight of 75 kg you are 68% of the way there, with 3.2 kg still to lose.

How to Use the Calculator

Pick your Weight unit — kg or lb. It applies to every weight you enter.
Enter your Starting weight (W₀) — your weight on the day you began your weight-loss effort.
Enter your Current weight (W₁) — your most recent weigh-in.
If you want goal tracking, keep Track a goal weight ticked and set your Goal weight (Wg). The tool then shows how much of the plan you have completed and an estimated date for reaching the goal at your current pace.
To see your body mass index, keep Show BMI (add your height) ticked and enter your Height in cm or inches. The result compares your starting and current BMI.
Set the Start date and Current date — the days your two main weigh-ins took place. These dates drive the weekly rate and the goal projection.
Optionally, paste intermediate weigh-ins into Weekly weigh-ins — one entry per line or separated by semicolons, each as a date and a weight (e.g. 2025-01-13 84.2). A plain number counts as the next weekly weigh-in after the start date. These points are plotted on the progress chart.

What Is Weight Loss Percentage?

Weight loss percentage describes how much of your starting body weight you have shed, rather than just the absolute number of kilograms or pounds lost. Losing 6.8 kg means one thing for an 85 kg adult and something quite different for a 120 kg person — as a percentage, both results are directly comparable. This is why many weight-loss programs, studies, and challenges measure progress in percent rather than raw weight.

The result also has a practical health meaning. For people who are overweight or obese, losing even 5% of body weight measurably improves blood pressure, blood sugar, and cholesterol, and a 10% reduction brings more pronounced benefits. Percentage is therefore a better milestone system than an arbitrary "target weight" picked in advance.

Interpreting your result is straightforward: a positive percentage means you are down from your starting weight, while a negative one means you have gained since the start. The calculator also reports your average weekly rate, both in weight units and as a percent per week. A pace of 0.5–1% of body weight per week is generally considered sustainable; much faster loss tends to come from crash dieting, loses muscle along with fat, and is rarely maintained afterward.

If you use the optional fields, you get extra context: goal progress tells you what share of your planned loss is complete and projects when you will finish if your current pace holds, and the BMI comparison shows whether your weight has moved you into a different BMI category. Remember that BMI is a rough screening tool — it does not distinguish muscle from fat. If you want a fuller picture, our ABS Body Shape Index calculator or the Army Body Fat calculator offer alternative measures of body composition.

Assumptions, Limitations and Practical Tips

Weigh consistently. Body weight swings by 1–2 kg day to day from water, food, and glycogen. Weigh yourself at the same time of day, ideally in the morning after using the bathroom, before eating or drinking.
The goal projection is an estimate. It assumes your average weekly rate stays constant, but real weight loss is rarely linear — plateaus and whooshes are normal. Treat the projected date as a rough guide, not a promise.
Watch the trend, not single points. The weekly log and chart exist for this reason. A single week up or down means little; the slope of the whole line is what matters.
Very fast loss is a warning sign. If the calculator flags a rate above 1% per week for an extended period, consider a smaller calorie deficit, more protein, and resistance training to protect muscle mass. Pairing the tool with our macronutrient calculator helps you set a sensible intake, and the steps-to-calories calculator can gauge your daily activity burn.
Losing too much too far? A weight loss percentage above roughly 10% in under three months, or a BMI sliding toward the underweight category, deserves a conversation with a doctor or dietitian.
Weight alone is not fitness. If you start strength training, you may lose fat while the scale barely moves. Body measurements, waist circumference, or how your clothes fit can show progress that this percentage cannot.

Frequently Asked Questions

How do I calculate weight loss percentage by hand?

Subtract your current weight from your starting weight, divide by the starting weight, and multiply by 100: \( \frac{W_0 - W_1}{W_0} \times 100 \). For example, from 200 lb down to 186 lb: \( \frac{14}{200} \times 100 = 7\% \). Always divide by the starting weight, not the current one, and the result is negative if you have gained.

What is a good or healthy weight loss percentage?

Losing 5% of your starting body weight already brings measurable health benefits, and 10% is a common milestone for people who are overweight. A sustainable pace is about 0.5–1% of body weight per week. Losses beyond that for extended periods often sacrifice muscle and water rather than fat. If you are not overweight, talk to a doctor before aiming for significant loss.

How do I convert my result between kg and lb?

The percentage itself is unit-free, so 8% is 8% whether you weigh yourself in kilograms or pounds. Only the absolute amounts converted. To translate the lost weight, multiply by 2.205 to go from lb to kg, or by 0.4536 to go from kg to lb: converting our example, a 6.8 kg loss equals 0.4536 × 6.8, which is 15 lb.

How many kilograms or pounds is 5% or 10% of my body weight?

Multiply your starting weight by 0.05 for 5% and 0.10 for 10%. A 90 kg person loses 4.5 kg at 5% and 9 kg at 10%; a 250 lb person loses 12.5 lb and 25 lb respectively. These small-sounding targets are clinically meaningful, which is why doctors often set them instead of an ideal-weight goal.

Why did my percentage go up even though my weight didn't change this week?

It didn't recalculate — more likely your weekly rate average shifted. The calculator uses only your starting and latest weigh-ins for the percentage, so a stalled week leaves that number untouched. However, including a stalled week in the average lowers your weekly rate, since the same total loss is now spread over more time.

Does weight loss percentage work the same for children or during pregnancy?

No, this calculator is designed for adults following a deliberate weight-loss plan. Children and teens need growth-aware assessment, and weight loss during pregnancy should only happen under medical supervision. Large losses in these groups — or any unexplained loss above roughly 5% in 6–12 months — warrant a conversation with a healthcare provider.

What's the difference between weight loss percentage and goal percentage?

Weight loss percentage divides what you lost by your starting weight, while goal percentage divides it by your total planned loss. Losing 6 kg out of a 10 kg plan is 60% of the goal, but if you started at 100 kg it is only 6% of body weight. The first tells you the health impact, the second tells you how far along your personal plan you are.