Percentage Calculator — X% of Y, What % of, Reverse %, % Change

Instant results. Private by design—everything runs locally in your browser.

Calculations

Find X% of Y

Tips, discounts, VAT, markups—enter a percent and a base.

%
?
Result: —

What percent is A of B?

Great for test scores, statistics, ratios, tax rates.

?
Result: —

Reverse a Percentage (Find the Original Number)

If A is B% of the original, what was the original?

% of what?
Result: —

Percent Increase/Decrease

Percent change = (New − Old) ÷ Old × 100.

Result: —

Quick Reference

  • X% of Y → (X / 100) × Y
  • What % is A of B → (A / B) × 100
  • Reverse % (“A is B% of what?”) → A ÷ (B / 100)
  • % Change → ((New − Old) / Old) × 100

Tip: Press Ctrl/Cmd + K to focus site search.

Percentage Examples

  • 20% of 150 = 30
  • What percent is 30 of 120? → 25%
  • 25 is 10% of what? → 250
  • From 80 to 100 is a 25% increase

5 Fun Facts about Percentages

Percent literally means “per 100”

The % symbol came from the Italian per cento (for 100). Writing 12.5% is just “12.5 per hundred.”

Origins

Stacked percents multiply

10% of 10% is 1% because 0.10 × 0.10 = 0.01. Chaining percentages multiplies them together.

Compound idea

Order of discounts matters

Two discounts don’t add: 20% off then 10% off is a 28% total cut, not 30%, because you’re compounding reductions.

Shopping math

Gains and losses aren’t symmetric

A 50% drop needs a 100% rise to get back. Percent change is directional; up and down aren’t mirror images.

Asymmetry

Percent vs percentage point

Moving a rate from 5% to 6% is a 1 percentage point shift, but it’s a 20% relative increase. Words matter.

Clear wording

About this Percentage Calculator

Percentages are a simple way to compare values, express change, or describe parts of a whole. This percentage calculator brings the most common percent questions into one place, so you can quickly solve everyday tasks like “What is 15% of 80?”, “30 is what percent of 120?”, or “If the price is 20% off, what was the original?”. It is designed to be fast, clear, and easy to use for students, shoppers, and professionals alike.

How percentages work in plain language

A percent means “per hundred.” So 25% is the same as 25 out of 100, or 0.25 as a decimal. When you take X% of Y, you are multiplying Y by X/100. When you ask What percent is A of B?, you are comparing A to B by dividing A by B and converting to a percentage. And when you ask A is B% of what?, you are reversing the process to find the original whole.

How to use this calculator

  1. Choose the question type: percent of a number, percent that one number is of another, reverse percent, or percent change.
  2. Enter the two values shown in the form (for example, a percentage and a number, or an old and new value).
  3. Click Calculate to see the result, then copy it or clear the inputs to try another scenario.

Common real-world uses

Percentages show up everywhere: shopping discounts, sales tax, interest rates, test scores, recipe scaling, and business metrics like conversion rate or growth. If a store advertises 30% off, this tool shows the sale price instantly. If your grade moved from 72 to 84, the percent change feature explains the improvement. If a product is now $60 after a 25% discount, the reverse percent option finds the original price.

This calculator also keeps your numbers private because it runs entirely in your browser. Use it as a quick reference for homework, budgeting, or data analysis whenever you need a clear, reliable percent calculation.

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