OptiDrop

Percentage Calculator Online — Free & Instant

Calculate any percentage in seconds. Find what percent one number is of another, compute percentage increase or decrease, and more. No upload, no sign-up — 100% free.

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Free Online Percentage Calculator

OptiDrop's Percentage Calculator is a free, browser-based tool that helps you solve any percentage problem instantly. Whether you need to find what percentage one number is of another, calculate a percentage of a value, or determine the percentage increase or decrease between two numbers, this tool handles it all. No downloads, no sign-ups, and no data leaves your device.

Three Calculation Modes

Switch between three common percentage calculations using the tab buttons: "What is X% of Y?" for finding a portion of a number, "X is what percent of Y?" for determining the ratio between two values, and "Percentage change from X to Y" for measuring growth or decline. All results update in real time as you type.

How Percentage Calculations Work

A percentage represents a fraction of 100. To find X% of Y, multiply Y by X and divide by 100. To find what percent X is of Y, divide X by Y and multiply by 100. For percentage change, subtract the original from the new value, divide by the original, and multiply by 100. Our calculator applies these formulas instantly so you never have to compute manually.

Frequently Asked Questions

To calculate a percentage, divide the part by the whole and multiply by 100. For example, to find what percentage 25 is of 200, compute (25 / 200) x 100 = 12.5%. Our percentage calculator does this instantly for you.
To find X percent of Y, multiply Y by X and divide by 100. For example, 20% of 150 = (20 / 100) x 150 = 30. Use the "What is X% of Y?" tab in our calculator for instant results.
Percentage increase is calculated by subtracting the original value from the new value, dividing by the original value, and multiplying by 100. Formula: ((New - Original) / Original) x 100. For example, going from 80 to 100 is a 25% increase.
Percentage decrease is calculated by subtracting the new value from the original value, dividing by the original value, and multiplying by 100. Formula: ((Original - New) / Original) x 100. For example, going from 100 to 75 is a 25% decrease.

Last updated: June 2026