Quick answer
Weight loss percentage = (start − current) ÷ start × 100. Dropping from 200 to 180 is a 10% loss, or 20 units.
Enter starting and current weights in the same unit. The calculator returns the percentage and amount lost.
Related tools: Weight Gain Calculator: Daily calorie surplus for a target weekly weight gain. Weight Change Rate Calculator: Average weight change per week and as a share of starting weight.
How to use the Weight Loss Percentage Calculator
- Enter starting weight (above 0).
- Enter current weight (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Starting weight | A number | > 0 |
| Current weight | A number | > 0 |
Formula and method
Formula
% lost = (start − current) ÷ start × 100
IEEE-754 double precision; shown to the decimals indicated.
Use the same unit for both weights; a negative result means weight gain. Informational estimate, not medical advice. Talk to a qualified health professional about your own situation.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Starting weight = 200; Current weight = 180.
| Result | Value |
|---|---|
| Weight lost | 10% |
| Amount lost | 20 |
Example 2
Inputs: Starting weight = 82.5; Current weight = 78.1.
| Result | Value |
|---|---|
| Weight lost | 5.33% |
| Amount lost | 4.4 |
Example 3
Inputs: Starting weight = 70; Current weight = 72.
| Result | Value |
|---|---|
| Weight lost | -2.86% |
| Amount lost | -2 |
The first line is the headline result (weight lost). Below it the weight Loss Percentage Calculator lists amount lost, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Why percentages
Percent lost allows fair comparison between people of different sizes. A 5% loss is associated with measurable improvements in blood pressure and blood sugar in some studies, and 10% with greater benefit.
Reading it
Use the same unit and the same scale conditions. Short-term numbers include water changes, so look at trends over weeks. Starting weight must be above zero.
How the result changes with starting weight
Holding every other input at the first worked example, this table changes only starting weight. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Starting weight | Weight lost | Amount lost |
|---|---|---|
| 100 | -80% | -80 |
| 200 | 10% | 20 |
| 400 | 55% | 220 |
| 800 | 77.5% | 620 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Starting weight: entering "0" shows "Starting weight must be greater than 0." beside that field and no result.
- Current weight: entering "-1" shows "Current weight must be greater than 0." beside that field and no result.
Choosing between the Weight Loss Percentage Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Weight Loss Calculator](/health/weight-loss-calculator/) | units, current weight and goal weight | Days to reach goal |
| [Weight Gain Calculator](/health/weight-gain/) | units and gain per week | Daily calorie surplus |
| [Weight Change Rate Calculator](/health/weight-change-rate-calculator/) | units, starting weight and ending weight | Change per week |
| [Calorie Deficit Calculator](/health/calorie-deficit-calculator/) | units, weight to lose and time | Daily calorie deficit |
| [Ideal Weight Calculator](/health/ideal-weight-calculator/) | units, sex and height | Ideal weight (Devine) |
Background: body measurements and screening
Body-measurement ratios are screening tools, not diagnoses. BMI ignores body composition and fat distribution, and reviews find waist-to-hip and waist-to-height ratios are useful additions but not clearly better than BMI or waist circumference alone. Where the tape goes matters, so measure at the same sites each time.
Some sources quote a waist-to-hip ratio above 0.8 for women and 0.95 for men as a marker of increased metabolic risk; treat that as a screening flag, and talk to a clinician about what your own numbers mean.
Assumptions and limitations
- Same unit for both weights
- Not a diagnosis
This calculator gives general information based on published formulas. It is not medical advice, and it cannot account for your health history. Talk to a qualified clinician about decisions that affect your health.
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for starting weight and current weight to confirm this.
Frequently asked questions
What is a healthy percentage?
About 5 to 10% over six months is a common goal.
How do I compute percentage gained?
(current − start) ÷ start.
Is 10% too fast?
Depends on the time frame.
What does the Weight Loss Percentage Calculator calculate?
Percentage of starting weight lost. It returns Weight lost and Amount lost.
What formula does the Weight Loss Percentage Calculator use?
% lost = (start − current) ÷ start × 100. Use the same unit for both weights; a negative result means weight gain.
What do I need to enter in the weight Loss Percentage Calculator?
You enter Starting weight and Current weight.
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Same unit for both weights.
What are the limits of this calculator?
Same unit for both weights. Not a diagnosis.
What is an example of a weight Loss Percentage result?
With starting weight 200 and current weight 180, the weight lost is 10%.
Can I rely on this calculator for a decision?
This calculator gives general information based on published formulas. It is not medical advice, and it cannot account for your health history. Talk to a qualified clinician about decisions that affect your health. For this calculator in particular: Same unit for both weights.
Related calculators
- Weight Gain Calculator — Daily calorie surplus for a target weekly weight gain.
- Weight Change Rate Calculator — Average weight change per week and as a share of starting weight.
- Ideal Weight Calculator — Ideal body weight by four published formulas (Devine, Robinson, Miller, Hamwi).
- Water Weight Calculator — Weight of a volume of water at a given temperature.
Sources
- Common definition used on this page. No single authoritative standard defines it, so the exact formula is stated in the formula section above
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.