Find 15% of 200
Input and settings
Mode: B% of A / A: 200 / B: 15
Expected result
30
Percentage Calculator
Calculate a percentage of a value, a value's share of a total, or a percentage change.
How to use
These are example steps; replace the values for your task.
- Select change from A to B.
- Enter 80 as the first value and 100 as the second.
Enter values
Result
About this tool
Switch between three common percentage calculations without rewriting a formula. It is useful for comparisons, reports, and checking changes between two values.
Percentage change uses the absolute value of the starting number as its reference. A change from zero is undefined, so the tool shows an error instead of a misleading result.
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The same 50 and 200 answer different questions
“50 is what percent of 200?” gives 25%. “What is the change from 200 to 50?” gives a 75% decrease. By contrast, “What is 50% of 200?” gives 100.
- The base value changes with the selected calculation. Read the field labels before entering the two numbers.
- Percentage change is undefined when the original value is zero. Currency rounding and tax rules are outside this calculation.
Try a use case and check the result
Distinguish a share of a total from a change measured against the original value.
Example buttons replace the inputs and settings above and calculate. Restore previous input returns to the state before the latest example.
After trying multiple examples, repeat Restore previous input to return to your original input. History is kept only in this page; restore any input you need before closing it.
Measure growth from 80 to 100
Input and settings
Mode: change from A to B / A: 80 / B: 100
Expected result
+25% (increase) (100 − 80) ÷ 80 × 100
How to read the result
The first result, 30, is an amount. For change, the original 80 is the denominator, giving 25%. Dividing the difference of 20 by the new 100 would instead give 20%. The ratio mode uses B as its denominator.
Scope and limits
Change uses the absolute original value as its denominator. Ratio B and change A are rejected when their absolute value is below 10⁻¹². Calculated values are cleaned to ten decimal places and may have floating-point error. A percentage change differs from a percentage-point difference.
Verification: existing calculatePercentage checks cover 200×15÷100, (100−80)÷80×100 and rejection of a zero reference, compared with the value and trend on screen.
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Choose the question before entering values
A change from 80 to 100 is a 25% increase.
Percentage change is (new − old) ÷ absolute value of old × 100.
Display uses up to 10 decimal places; this is separate from rounding to a currency unit.
Frequently asked questions
Can I use decimals and negative numbers?
Yes. Decimals and negative values are supported, and floating-point noise is removed from the displayed result.
What happens when the starting value is zero?
A conventional percentage change from zero is undefined, so the tool displays an error.
Are my values saved?
No. Values are not saved, and the calculation runs entirely in your browser.
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Inputs and storage
Keep any content you need before clearing. This tool does not autosave inputs or results. Reloading or closing the page, clearing inputs or resetting may discard your work.
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