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Percentage Calculator

Calculate X% of a number, find what percent one value is of another, reverse a percentage, compare percentage change, and work out percentage difference, discounts, increases, and decreases.

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Result

Enter values to see the result

Common Scenarios

Basic

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Percentage Calculator

Quick Start

1
Choose the calculation mode that matches your question.
2
Enter the numbers required for that mode.
3
Read the result, formula, and summary.

Common Scenarios

Use this for questions like "what is 20% of 150?" to turn a percentage into a number.

Use this for shares, completion rates, ratios, and questions like "30 is what percent of 150?"

Use this for questions like “30 is 20% of what?” when you know the part and the percent but not the whole.

Compare an old value and a new value to see the relative increase or decrease.

Use this for markup, growth, tax, tips, or any value raised by a percentage.

Use this for discounts such as 20% off, price cuts, deductions, or values reduced by a percentage.

Use this when you know the final value after a percentage increase or decrease and need the original value.

Compare two values symmetrically using the average of their absolute values as the baseline.

Choose the Right Calculation

Choose percent of a value when a percentage should become a number, such as 20% of 150.
Choose part as a percent of whole when a number should become a share, such as 30 out of 150.
Choose find the whole when the question is “X is P% of what?”, such as 30 being 20% of 150.
Choose percentage change when the question compares before and after values, such as 100 to 125.
Choose add percentage for markup, growth, tax, tips, or a price increase.
Choose subtract percentage for discounts, markdowns, deductions, shrinkage, or a price decrease.
Choose reverse percentage when a final price or final value already includes a percentage increase or decrease.
Choose percentage difference when neither value should be treated as the original baseline.

Formula & Mode Matrix

Percent of a value: enter percentage and value; percentage ÷ 100 × value returns the amount represented by X% of that value.
Part as a percent of whole: enter part and whole; part ÷ whole × 100 returns what percent one value is of another.
Find the whole: enter part and percentage; part ÷ (percentage ÷ 100) returns the missing whole value.
Percentage change: enter original and new value; (new value - original value) ÷ original value × 100 returns the increase or decrease relative to the original baseline.
Add percentage: enter percentage and value; value × (1 + percentage ÷ 100) returns the final value after markup, growth, tax, tips, or increase.
Subtract percentage: enter percentage and value; value × (1 - percentage ÷ 100) returns the final value after discount, markdown, deduction, or decrease.
Reverse percentage: enter final value, percentage, and increase/decrease direction; divide by (1 + percentage ÷ 100) or (1 - percentage ÷ 100) to recover the original value.
Percentage difference: enter two values; |first value - second value| ÷ average(|first value|, |second value|) × 100 returns the symmetric difference between them.

Read the Result Correctly

Read the unit first: percent-of, add, and subtract return a value; ratio and change return a percentage.
Percentage change is relative to the original value: 50 to 100 is +100%, while 100 to 50 is -50%.
Percentage difference uses the average of the two absolute values as its baseline, so it is not the same as percentage change.
Reverse percentage divides by the remaining or increased factor; 20% off means the final value is 80% of the original.
Percentage points are direct gaps between percentages: 20% to 25% is +5 points, not +5%.
Consecutive percentage changes use the updated value each time; +20% then -20% turns 100 into 96.
If the whole or original value is 0, ratio and change have no valid baseline, so the result is undefined.

Usage Advice

You can enter decimals, percent signs, and grouped numbers such as 12.5, 12,5, 20%, or 1,234.56.
When a calculation needs a baseline, the whole or original value cannot be 0.
Displayed results are rounded to at most four decimal places, so use the formula if you need audit-level precision.

URL Quick Fill

Prefill this tool from the URL hash. Use the parameter pair for the calculation view; if view is missing, CrateX.app infers it from parameter names when possible.
view: Calculation view (optional: percent-of, what-percent, find-whole, percentage-change, add-percent, subtract-percent, reverse-percentage, percentage-difference)
percent: Percentage
value: Base value for percent-of, add, or subtract
part: Known part
whole: Whole value
original: Original value
new-value: New value
final-value: Final value
direction: Reverse direction (increase or decrease)
first-value: First value
second-value: Second value
Example: #view=reverse-percentage&final-value=120&percent=20&direction=increase
Hash parameters stay in the browser for tool prefill; CrateX.app does not record them.
Do not put private amounts, client names, or other sensitive details in URLs.

Limitations & Compatibility

Ratio and percentage-change calculations need a non-zero baseline; otherwise the result has no mathematical meaning.
A 100% decrease leaves no remaining baseline, so the original value cannot be recovered from the final value.
Formal financial work may require your own rounding rule, especially for currency, tax, invoices, or reports.
Do not mix percent change with percentage points; 20% to 25% is +5 points but +25% relative change.
Multiple percentage changes cannot simply be added; tax, fees, compounding, and order of operations can change the final result.

Privacy & Security

Calculations run in your browser. Current values stay in the current browser session by default.

FAQ

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