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Weight Loss Percentage Calculator

Express the weight you have lost as a percentage of your starting weight, with optional progress toward a goal weight.

Level: Grade 7

  • Common Core standard 7.RP.A.3Use proportional relationships to solve multistep ratio and percent problems. Examples: simple interest, tax, markups and markdowns, gratuities and commissions, fees, percent increase and decrease, percent error.
Printable worksheet

Weight Loss Percentage Calculator

Know the answer you need? Pick an input to work backward.

Inputs
Units

Your weight when you began, in the unit chosen above.

Weigh at the same time of day, on the same scale, for a fair comparison.

Leave blank to skip the progress-to-goal figure.

Result

Percent of starting weight lost

8%

You have lost 16 lb, or 8% of your starting weight.

Weight lost
16 lb
Current weight as a share of starting weight
92%

See the step-by-step solution ↓

Step-by-step solution

  1. Weight lost is the starting weight minus the current weight

    200 lb−184 lb=16 lb

  2. Divide by the starting weight and multiply by 100 to express it as a percentage

    16200×100=8%

Test yourself

20 quick questions built from this calculator's formula: work out results, predict what happens when an input changes, and work backward from an answer. Every answer comes with the working.

Please note: This calculator gives a general screening estimate, not a diagnosis. Talk to a qualified healthcare professional about your individual health.

What this calculator does

See what share of your starting weight you've lost, as a simple percentage. A loss of 10 pounds means something different to someone who started at 140 pounds than to someone who started at 280. A percentage of the starting weight puts both on the same scale. That's why weight change is often reported this way. You'll see it in fitness tracking, weigh-in challenges and research summaries.

Enter your starting and current weights in pounds or kilograms. You'll see the percentage lost, the amount lost, and what share of your starting weight you weigh now. Add a goal weight if you like, to see how far along you are. The calculator only does arithmetic. It doesn't judge whether an amount or pace of weight change is right for you. That's a conversation for a doctor or dietitian.

Where it's used

Why this math matters outside the classroom:

  • Weigh-in challenges. Office challenges rank people by percent lost, so 12 lb from 240 lb (5%) ties with 9 lb from 180 lb (5%).
  • Class percent decrease. Students practise percent decrease by finding that a drop from 200 to 184 is 16 ÷ 200, which is 8%.
  • Coaching check-ins. Trainers log each client's change as a percentage so progress can be compared across clients of different sizes.
  • Goal progress. Someone aiming to go from 200 lb to 170 lb who has lost 15 lb is exactly halfway, 50% of the planned 30 lb.
  • Pet weight tracking. Owners following a vet's plan see that a dog going from 50 lb to 47 lb has lost 6% of its starting weight.

Grade level and standards: Grade 7; Common Core State Standards for Mathematics 7.RP.A.3. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.

How to use it

  1. Pick pounds or kilograms. Both weights use the same unit, so nothing needs converting.
  2. Enter the weight you started at and your weight now.
  3. Optionally add a goal weight to see progress toward it as a percentage.
  4. Read the percent lost, the amount lost and the progress figure. Open the steps to see how each number was worked out.

What the inputs mean

Starting weight
The weight at the point you want to measure from, such as the first weigh-in of a program.
Current weight
Body weight moves by a pound or two from day to day with water and food. A weekly average, or weighing at the same time each day, gives a steadier figure.
Goal weight (optional)
Optional. It must be below the starting weight for progress to make sense.

Formula and method

weight lost = starting weight − current weight
percent lost = (starting weight − current weight) ÷ starting weight × 100
progress toward goal = weight lost ÷ (starting weight − goal weight) × 100

This is the everyday formula for a percent decrease. The starting weight is the base, the number everything is compared with. Weight lost is the starting weight minus the current weight. Dividing by the starting weight and multiplying by 100 turns it into a percentage. The unit doesn't matter: 16 lb out of 200 lb and 7.26 kg out of 90.72 kg are both 8%.

If the current weight is higher than the starting weight, the result is negative, which shows a gain. Progress toward a goal compares the weight lost so far with the total you planned to lose. It can pass 100% if you go beyond the goal.

Worked example

Someone started at 200 lb and now weighs 184 lb. Their goal weight is 170 lb.

  1. Weight lost = 200 − 184 = 16 lb.
  2. Percent lost = 16 ÷ 200 × 100 = 8%.
  3. Planned loss = 200 − 170 = 30 lb, so progress = 16 ÷ 30 × 100 = 53.3%.
  4. Reaching the goal would be a loss of 30 ÷ 200 × 100 = 15% of the starting weight.

Result: They have lost 8% of their starting weight and are 53.3% of the way to their goal, with 14 lb to go.

Understanding the result

The percentage is a fair way to compare change between people of different sizes. It also lets you compare your own progress at different times.

Week-to-week numbers bounce around with water, salt and meal timing. So the trend over several weeks says more than any single weigh-in.

A figure from this calculator describes change; it isn't a health assessment. Whether an amount or pace of change suits you depends on the person. A healthcare professional is the right person to advise on it.

Assumptions and limitations

  • Both weights are in the same unit and measured on the same scale under similar conditions.
  • The starting weight is the base for every percentage, as in an everyday percent decrease.
  • Results are rounded for display, but the math behind them isn't rounded.
  • Body weight alone doesn't show whether the change came from fat, muscle or water.
  • Daily fluctuations can make a single reading misleading.
  • The calculator doesn't recommend targets or rates of loss.

Frequently asked questions

How do I calculate the percentage of weight I have lost?

Subtract your current weight from your starting weight. Divide by the starting weight, then multiply by 100. From 180 lb down to 171 lb, that's 9 ÷ 180 × 100 = 5%.

Does it matter whether I use pounds or kilograms?

No. The percentage compares two weights in the same unit, so the unit cancels out. Just be sure both weights use the same one.

Why does the percentage get smaller for the same number of pounds as I go?

It doesn't, because every percentage here is measured against the starting weight. You could measure each week's loss against the previous week's weight instead. Then the base shrinks and the figures shift slightly. That's why this calculator keeps one fixed starting point.

What does a negative result mean?

It means the current weight is above the starting weight, so the change is a gain. The amount is shown as a negative loss.

Can progress toward my goal go over 100%?

Yes. If you pass your goal weight, progress is more than 100% and the calculator shows how far past the goal you are.

How this calculator is checked

Method: Standard percent-decrease formula with the starting weight as the base; progress toward a goal as the ratio of weight lost to planned loss. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.

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