Percentage Calculator — Free Online Tool
Calculate percentages in 3 different ways
How to use this tool
- [01]Choose the calculation mode you need: X% of Y, X is what percent of Y, or percentage increase/decrease.
- [02]Enter the two numbers the selected mode asks for.
- [03]Read the result instantly — switch modes at any time without losing your entered numbers.
About this Percentage Calculator
The Percentage Calculator covers the three questions that come up most often with percentages, each in its own mode: finding what X% of a number Y is, working out what percentage one number is of another, and calculating the percentage increase or decrease between two values. Each mode uses its own formula rather than forcing every question through a single generic calculation, since the three questions aren't actually the same math despite all involving percentages.
The increase/decrease mode is the one people most often get backwards by hand: percentage change is always calculated relative to the original (starting) value, not the new one, so going from 50 to 75 is a 50% increase, but going from 75 back down to 50 is a 33.3% decrease, not 50%, because the base number changed. The calculator handles this correctly regardless of which direction the change goes.
Typical uses span pricing (working out a markup or markdown), analytics (a month-over-month percentage change in traffic or sales), and everyday math (splitting a bill, checking a stated discount, or verifying a tip). Because each mode is explicit about which numbers are inputs and which is being solved for, there's less room to misapply the wrong formula compared to doing the arithmetic manually.
Everything calculates instantly as you type, entirely client-side.
Our Percentage Calculator is completely free to use with no signup required. For this tool, processing runs in your browser — your files and data stay on your device and are not uploaded to our servers.
Whether you are a developer, designer, student, or business owner, this tool is designed to save you time and make your workflow more efficient. Bookmark this page to access it whenever you need it — it will always be free.
Frequently asked questions
Is the Percentage Calculator completely free?
Yes, the Percentage Calculator is 100% free to use with no hidden charges, no subscription, and no signup required. Simply visit the page and start using it immediately.
Does this tool upload my files to a server?
No. Everything runs entirely in your browser using JavaScript. Your files, text, and data never leave your device and are never sent to our servers. This makes it completely private and secure.
Does the Percentage Calculator work on mobile?
Yes, the Percentage Calculator is fully responsive and works on all devices including smartphones, tablets, and desktop computers. It works on Chrome, Firefox, Safari, and Edge browsers.
How accurate is this tool?
Our Percentage Calculator uses industry-standard algorithms to ensure accurate results every time. It has been tested extensively across different browsers and devices to ensure consistent and reliable output.
Why is a 50% increase followed by a 50% decrease not back to the original number?
Because percentage change is calculated against a different base each time. Increasing 100 by 50% gives 150; decreasing 150 by 50% gives 75, not 100 — the base number changed between the two calculations.
Which mode do I use to find a discount amount?
Use ‘X% of Y’ with the discount percentage and original price to find the amount taken off, or the increase/decrease mode if you already know both the original and sale price and want the percentage.
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