Percentage Calculator — Free Percent Change, Increase & Difference Calculator

Percentage Calculator — Free Percent Change, Increase & Difference Calculator. Free percentage calculator: find X% of Y, what percent X is of Y, percent change (increase/decrease), percentage difference, reverse percentage and percent error — with formulas.

Our free percentage calculator solves every everyday percent problem on one page, with the working shown.

Find X% of Y (what is 15% of 80?), work out what percent X is of Y (x is what percent of y — handy for test scores, budgets and conversion rates), and use the percent change calculator to measure growth or decline between an old and a new value.

The result is labelled as an increase or a decrease, so the same card doubles as a percentage increase calculator and percentage decrease calculator for prices, salaries, traffic, revenue and stock moves.

Go further with a percentage difference calculator that compares two values relative to their average (the symmetric formula used in science and statistics), a tool to add or subtract a percentage from any number (for example a 15% raise or a 20% reduction), a reverse percentage calculator that finds the original whole when you only know a part and its percentage, and a percent error calculator for lab reports that compares a measured value with the true value.

Every card prints its formula with your numbers — a quick lesson in how to calculate percentage step by step. Shopping? Use the dedicated Discount Calculator for sale prices, or the Tip Calculator to split a restaurant bill.

Choose how many decimal places to show, or keep full precision without floating-point noise such as 0.30000000000000004.

Load an example to see every calculator in action, copy any result with one click, clear all fields, or share a link that restores your numbers. All maths happens locally in your browser, so budgets, grades and business figures never leave your device.

Related tools: Math Evaluator for free-form expressions, Compound Interest Calculator for growth over time, Mortgage Calculator and Body Fat Percentage Calculator.

Frequently asked questions

How do I calculate a percentage of a number?

In the first card, type the percentage in X and the number in Y. For example, 25 % of 200 shows 50, together with the working 25 ÷ 100 × 200 = 50. Use the copy icon in the result box to copy it.

How do I work out a percentage increase or decrease?

Enter the old value in From and the new value in To. The calculator shows (To − From) ÷ From × 100 and labels the result as Increase, Decrease or No change, so going from 80 to 100 is a 25% increase.

What is the difference between percent change and percentage difference?

Percent change measures movement from a starting value, so the order of the numbers matters. Percentage difference compares two values against their average, the absolute difference divided by the mean, so swapping them gives the same answer. Use it when neither value is the reference.

How do I find the original number with a reverse percentage?

Use the reverse percentage card: enter the value you know and the percentage it represents. For example, 30 is 20% of 150. The tool divides the value by the percentage and multiplies by 100.

Why is a result blank, and how do I round it?

A result stays empty until both fields in that card contain numbers, and also when the maths is undefined, such as a percent change from 0. Set Decimal places from 0 to 10 to round every result, or leave it empty for full precision.

How to use this online tool

Percentage Calculator — Free Percent Change, Increase & Difference Calculator is designed for fast browser workflows when you need to format, validate, convert, decode, encode, generate, or inspect data without opening a heavy desktop app. Start with the input field or visible options, review the result, then copy or download the output for the next step.

Private processing in your browser

Percentage Calculator — Free Percent Change, Increase & Difference Calculator keeps the normal processing step local in your browser. That is useful for code snippets, tokens, documents, configuration values, text samples, and other material that should not be sent to a remote service unless you explicitly choose to share it.

When this tool is useful

Use Percentage Calculator — Free Percent Change, Increase & Difference Calculator for repeatable developer tasks, technical documentation, QA checks, quick conversions, debugging, content cleanup, and internal team workflows. The page focuses on clear inputs, immediate feedback, and output that is easy to reuse in code, reports, tickets, emails, or notes.

Practical tips

Before copying the final result, check important details such as spacing, casing, filenames, encoding, token structure, line breaks, or output format. Small checks prevent mistakes when the result is reused in source code, API requests, documentation, spreadsheets, or shared files.