WiseCalcs

Percentage calculator

Three common percentage questions in one place. Pick a mode, type two numbers, and the answer updates as you go.

Use it to find X% of a number, to see what percent one number is of another, or to measure the percentage change from one value to the next.

What do you want to work out?
%

Result

30

The result updates as you type. Use the buttons at the top to switch between the three questions.

How does it work?

1. What is x% of y. 2. x is what percent of y. 3. Percentage change from x to y.

Percentage formulas

1.y⋅x1002.xy⋅1003.y−xx⋅100\begin{aligned} &\textbf{1.}\quad y \cdot \tfrac{x}{100}\\[2pt] &\textbf{2.}\quad \tfrac{x}{y} \cdot 100\\[2pt] &\textbf{3.}\quad \tfrac{y-x}{x} \cdot 100 \end{aligned}
x
First value: the percent, the part, or the starting value.
y
Second value: the base, the whole, or the new value.

20% of 150 = 30. 30 is 20% of 150. From 150 to 180 is a 20% increase.

Method & sources

Inputs are treated as plain numbers without units or currency. Percentage change uses the first value as the baseline.

Sources

Where this method comes from — use these references to understand the formula, assumptions, and limits.

How we calculate

  • Inputs are treated as plain numbers without units or currency.
  • Percentage change uses the first value as the baseline.

Rounding

Results are rounded to two decimals for display. The calculation itself uses full precision.

What this calculator does

Percentages answer three everyday questions, and this calculator handles all of them. You can take a percentage of a number, express one number as a percentage of another, or measure how much a value went up or down in percentage terms.

How to use it

  1. Choose the question you want to answer at the top.
  2. Type the two numbers. The labels change to match the mode.
  3. Read the result and the bar below it.

A worked example

Say a 150 kr item is marked up to 180 kr. Switch to “Change X → Y”, enter 150 and 180, and you get +20%. Switch to “X% of Y”, enter 20 and 150, and you get 30 — the size of that increase.

Common mistakes

  • Mixing up the part and the whole. The whole is the number you compare against.
  • Reading a percentage change as a final value. A +20% change on 150 is an increase of 30, ending at 180.
  • Expecting percentages to stay under 100%. A part larger than the whole is over 100%, which is correct.

When it's useful

Tips, discounts, test scores, price changes, and quick sanity checks on numbers you see day to day.

FAQ

How do I calculate a percentage of a number?
Pick “X% of Y”, enter the percentage and the value. For 20% of 150 you get 30.
How do I find what percent one number is of another?
Pick “X is what % of Y”, enter the part and the whole. 30 out of 150 is 20%.
What does percentage change mean?
It compares a new value to an old one, relative to the old one. Going from 150 to 180 is a 20% increase; going from 180 to 150 is a 16.67% decrease.
Why is my percentage above 100%?
When the part is larger than the whole, the percentage is above 100%. That is expected, not an error.
Are results rounded?
Results are shown rounded to two decimals. The calculation behind them uses full precision.
Can I share a calculation?
Yes. Use Share to copy a link that reopens the calculator with the same mode and numbers.

Related calculators

Embed this calculator

Add this calculator to your own site. The snippet includes the calculator iframe and a small attribution link:

<iframe src="https://wisecalcs.com/embed/en/percentage-calculator" width="100%" height="520" style="border:0" loading="lazy"></iframe> <p>Calculator from <a href="https://wisecalcs.com/en/math/percentage-calculator">WiseCalcs</a></p>