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Percentage Calculator

Free online percentage calculator. Quickly calculate percentages, percentage increase/decrease, and ratios with our easy-to-use tool.

%

Result

170

20% of 850 = 170

Quick insights

  • Half of 850 is 425.
  • 10% of 850 is 85.

Popular Percentage Calculations

1% of 10 1% of 20 1% of 25 1% of 50 1% of 75 1% of 100 1% of 150 1% of 200 1% of 250 1% of 300 1% of 400 1% of 500 1% of 750 1% of 800 1% of 1000 1% of 1200 1% of 1500 1% of 2000 1% of 5000 1% of 10000 2% of 10 2% of 20 2% of 25 2% of 50 2% of 75 2% of 100 2% of 150 2% of 200 2% of 250 2% of 300 2% of 400 2% of 500

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Method

How this calculator works

Percentages are fractions of 100 expressed as a value. Every percentage problem reduces to multiplication or division — the mode you pick determines the formula.

X% of Y           =  (X / 100) × Y
Y increased by X% =  Y + (X / 100) × Y
Y decreased by X% =  Y − (X / 100) × Y
A is what % of B  =  (A / B) × 100
% difference      =  |A − B| / ((|A| + |B|) / 2) × 100
  1. Decide the mode that matches your question (X% of Y, increase, decrease, reverse, or difference).
  2. Plug both numbers into the corresponding formula above.
  3. For increase/decrease: multiply by (1 + X/100) or (1 − X/100) for a clean shortcut.
  4. For reverse-percent: divide the part by the whole, then multiply by 100.
  5. Round the result to the precision you need — 2 decimal places covers most everyday use.

Examples

Worked examples

Real numbers, end-to-end results.

20% of 850

= 170

Useful for tip, tax, or discount calculations.

$2,400 increased by 7.5%

= $2,580

A common annual-raise calculation.

300 is what % of 1,200?

= 25%

Reverse-percent: find the share, not the value.

Difference between 80 and 100

= 22.22%

Symmetric difference — useful for comparing experiments.

Use cases

When to use it

  • Calculate sales tax, tips, or store discounts on the fly.
  • Compare exam scores or growth rates.
  • Estimate annual salary raises or rent increases.
  • Convert ratios and proportions into something more readable.
  • Spot-check financial statements for percentage changes.

FAQ

Frequently asked questions

How do I calculate a percentage of a number?
Multiply the number by the percentage fraction. For example, 20% of 50 is (20/100) × 50 = 10.
What is percentage increase?
Percentage increase shows how much a value has grown compared to its original amount. Formula: ((New - Old) / Old) × 100.
How do I find out what percentage A is of B?
Divide A by B, then multiply by 100. For example, 5 is what percent of 20? (5/20) × 100 = 25%.
Can percentages be negative?
The percentage value itself is usually positive, but a percentage change can be negative, indicating a decrease.
Why is 50% of 10 the same as 10% of 50?
This is a mathematical rule called the commutative property of multiplication. X% of Y will always equal Y% of X.
Methodology, assumptions & limitations

How we calculate: This calculator uses standard, peer-reviewed mathematical formulas implemented in TypeScript. All calculations run entirely in your browser — no data is sent to any server.

Assumptions: Unless stated otherwise, calculations assume constant rates over the specified period, no taxes or fees beyond those explicitly input, and standard compounding conventions for the formula type.

Limitations: Results are estimates for planning purposes. Real-world outcomes may differ due to variable rates, regulatory changes, taxes, fees, inflation, or other factors not modeled. This tool does not constitute professional advice.

When NOT to use this: Do not rely solely on this calculator for critical decisions where exact precision is required beyond the decimal places shown.

Feedback: Found an error or have a suggestion? Contact us — we review and correct reported issues within 48 hours.

Deep Dive Guide

Percentage Change Calculator: Increase and Decrease Explained

Learn how to calculate percentage increase and decrease between two numbers, with the formula, worked examples, and the mistakes people make most.

Read Full Guide

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