What is the difference between "20% of 100" and "100 is what % of 20"?

The first finds a portion of a number (=20); the second compares two numbers as a ratio (=500%) — pick the matching mode for the question you actually have.

Why do percentage increase and decrease not cancel out?

Because each percentage is calculated against a different base — a 20% increase from 100 reaches 120, but a 20% decrease from 120 only drops back to 96, not 100.

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Percentage Calculator

Calculate percentage of a number, percentage increase/decrease, and proportions.

What is X% of Y?

What is% of=30.00

X is what % of Y?

is what % of=+12.50%

Percentage Increase or Decrease

Fromto=+25.00%

Quick Reference & Instructions

Simple steps, pro tips, and execution details

Enter Your Numbers

Type in your initial amounts, interest rates, or investment duration below.

Live Instant Calculation

Watch the charts, returns, and breakdown tables update immediately as you tweak numbers.

Copy or Plan Next Steps

Copy summary results or use the visual breakdown to make informed financial decisions.

How It Works

Provides instant answers for standard percentage scenarios (e.g. what is X% of Y, X is what % of Y, percentage difference).

Formula & Logic

Percentage = (Part / Whole) × 100 ; Change = ((New - Old) / Old) × 100

Example: A price increasing from $100 to $120 is a 20.00% increase.

Frequently Asked Questions

Common questions about calculations, assumptions, and edge cases.

Subtract the new value from the original, divide by the original value, then multiply by 100 — this tool handles that automatically for the "increase/decrease" mode.

In-Depth Guides & Tutorials

Explore all guides →

7 min read•finance

How to Calculate Percentages: Complete Beginner & Practical Guide

Master percentage calculations across all 3 standard scenarios: finding a percentage of a number, calculating proportions, and computing percentage increase or decrease.

Read Tutorial

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