Weight Loss Percentage Calculator
Written by the percentages.co.uk team. Reviewed for accuracy.
This calculator works out what percentage of your starting weight you have lost or gained. Enter your starting weight and your current weight in kilograms or pounds to see the result instantly with full workings.
How it works
Weight loss percentage measures how much of your original body weight you have lost, expressed as a percentage of that starting weight. It is more useful than the raw kilogram figure because it accounts for starting weight: losing 5 kg from 60 kg is proportionally more significant than losing 5 kg from 120 kg.
The formula
Weight lost % = ((Starting weight - Current weight) / Starting weight) × 100
A positive result means weight has been lost. A negative result (current weight higher than starting weight) means weight has been gained. The calculator labels this clearly.
Why this works: The formula is a standard percentage change calculation where the starting weight is the reference point. Using starting weight as the denominator ensures the percentage is always expressed relative to where you began.
Worked examples
Someone starts at 95 kg and drops to 82 kg. What percentage of their starting weight have they lost?
- Weight lost: 95 - 82 = 13 kg
- Weight lost %: (13 / 95) × 100 = 13.68%
Answer: 13.68% lost
A person weighs 14 stone (196 lbs) and loses weight to 12.5 stone (175 lbs). What percentage have they lost?
- Weight lost: 196 - 175 = 21 lbs
- Weight lost %: (21 / 196) × 100 = 10.71%
Answer: 10.71% lost
A gym participant sets a goal to lose 10% of their 78 kg starting weight. How much do they need to lose?
- Target loss: 78 × 0.10 = 7.8 kg
- Target weight: 78 - 7.8 = 70.2 kg
Answer: Lose 7.8 kg to reach 70.2 kg
A Slimming World member starts at 102 kg and reaches 91 kg over 6 months. What percentage have they lost?
- Weight lost: 102 - 91 = 11 kg
- Weight lost %: (11 / 102) × 100 = 10.78%
Answer: 10.78% lost
A weightlifter deliberately gains from 75 kg to 83 kg during a bulking phase. What percentage did they gain?
- Weight gained: 83 - 75 = 8 kg
- Weight gained %: (8 / 75) × 100 = 10.67%
Answer: 10.67% gained
When to use this
- NHS weight management programmes: Clinicians often set targets as a percentage of starting weight (typically 5-10%) rather than a fixed kilogram figure, as percentage loss is a better indicator of health benefit.
- Slimming clubs and challenges: Many UK slimming groups track member progress as a percentage of starting weight, making it fairer when comparing people of different sizes.
- Fitness challenges: Tracking progress for a charity fundraising event or workplace wellness scheme where participants start at different weights.
- Bariatric surgery monitoring: Surgeons and dietitians use percentage of starting weight lost to assess outcomes after procedures such as gastric bypass or sleeve gastrectomy.
Understanding the result
NHS guidelines suggest that losing 5-10% of starting body weight can have meaningful health benefits, including improved blood pressure, blood sugar and cholesterol levels. A loss of 5% or more is generally considered clinically significant.
Note that this calculator measures the percentage of starting weight, not body fat percentage. Two people who both lose 10% of their starting weight may have different body composition changes depending on whether the loss is fat, muscle or water.
Related concepts
➡ To express the change between any two values in percentage terms, use the percentage change calculator, which works for any starting and ending value. ➡ If you know the percentage change and want to find the original weight, the reverse percentage calculator works backwards from the percentage to the original value. ➡ For tracking progress towards a specific target, use the target vs achievement calculator to see how close you are to your goal.
How to do this in Excel
=((A1-B1)/A1)*100
Put your starting weight in A1 and your current weight in B1. A positive result means weight lost; a negative result means weight gained.
How to do this without a calculator
Subtract your current weight from your starting weight to find how much you have lost. Divide that by your starting weight. Multiply by 100. For example: starting at 90 kg, now 81 kg. Difference is 9 kg. 9 ÷ 90 = 0.1. Multiplied by 100 = 10%.
Common mistakes
Confusing percentage of weight lost with body fat percentage
This calculator measures what percentage of your starting body weight you have lost. Body fat percentage is a different measurement that requires body composition analysis.
Using current weight instead of starting weight as the denominator
The percentage must be calculated against the starting weight, not the current weight. Using the wrong denominator overstates the percentage lost.
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