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Percentage Calculator

Find a percent of a number, compare a part with a whole, or calculate percentage change.

Live calculator

Calculate a percentage

20% of 15030

Use this for discounts, taxes, tips, and quick percent math.

Percent of a number
Percent20.00%
Of number150

20 ÷ 100 × 150 = 30

Use this as a transparent math check. Percent, average, and fraction results can change if the denominator, original value, count, or rounding choice changes.

Which percentage tool should I use?Use the simpler calculator unless you are comparing an old and new value.
Percentage calculator (this tool)Use for percent of a number, part of a whole, or a direct percentage question.Percent changeUse when you are comparing an original value with a newer value.

Formula

Percentage formulas

X% of Y = (X / 100) x Y; percentage change = ((new - old) / |old|) x 100, when old is not zero

Use the first formula to find a percent of a number. Percentage change uses the absolute original value so its sign follows the numeric increase or decrease; the original value cannot be zero.

How to use

Steps

  1. Choose Percent of a number, Part of a whole, or Percentage change to match your question.
  2. Enter the two values shown for the selected task.
  3. Read the live result and relationship diagram as you change the inputs.
  4. Use Copy result or Copy link when ready. Clear inputs empties all three tasks; Reset example restores their example values.

Example

Sample calculation

20% of 15030
45 out of 6075%
80 to 10025% increase

Calculator use

Best for

  • Checking everyday percent, change, average, median, fraction, and decimal math before copying a result into another task.
  • Teaching, homework, shopping, reporting, budgeting, or spreadsheet checks where the formula matters as much as the number.

Before relying on it

Check first

  • Using the wrong denominator, original value, count, or operation for the math question being asked.
  • Rounding the result early and then reusing that rounded value in a second calculation.
  • Comparing an average, percentage, or fraction without checking whether outliers, zero values, or missing entries change the meaning.

Details

What to know before using the result

Percent meaningPer 100

Convert the percent to a decimal before multiplying. For example, 20% becomes 0.20.

Part and wholeOrder matters

When finding what percent one number is of another, divide the part by the whole and multiply by 100.

Percent changeUses the original value

Percentage increase or decrease compares the change with the original value, not the new value.

Source notes

References used for this calculator

OpenStaxCovers basic percent equations plus percent increase and percent decrease in Prealgebra 2e.

Benchmarks

How to read the result

0% - 10%: Small change.

Often useful for discounts, tax, tips, price moves, and small metric changes.

10% - 25%: Moderate change.

Large enough that most people will notice it in a bill, budget, or report.

25%+: Large change.

Usually worth double-checking the original numbers and assumptions.

Calculator accuracy

Methodology and assumptions

Formula, inputs, limitations and review record
Formula

X% of Y = (X / 100) x Y; percentage change = ((new - old) / |old|) x 100, when old is not zero

Inputs used

Percent, Base number, Part, Whole, Original value, New value

Limitations

Core math pages show standard formulas, but interpretation still depends on choosing the right denominator, operation, comparison period, and rounding point.

Review record

Catalog QA baseline on June 6, 2026. This date marks the catalog-wide automated and editorial QA baseline, not a tool-specific expert review.

Cite this page

Toolkit Shelf. Percentage Calculator. https://toolkitshelf.com/tools/percentage-calculator

FAQ

Common questions

How do I calculate a percentage of a number?

Divide the percentage by 100, then multiply by the number. For example, 20% of 150 is 0.20 x 150 = 30.

How do I calculate percentage increase?

Subtract the old value from the new value, divide by the old value, then multiply by 100.

What does percentage decrease mean?

Percentage decrease shows how much a value went down compared with the original value.

What is the most common percentage mistake?

The most common mistake is using the wrong whole. For example, 20 as a percent of 80 is different from 20 as a percent of 100.

Is percent change the same as percent of a number?

No. Percent of a number multiplies a base by a percent. Percent change compares a new value with an original value.