% Percentage Calculator

Calculating percentages is one of the most common math tasks in everyday life — from figuring out a restaurant tip to understanding a salary raise, a discount at checkout, or an exam score. Doing this math by hand is easy to get wrong, especially under time pressure. The Percentage Calculator instantly solves the most common percentage problems: finding what percent one number is of another, finding a percentage of a number, and calculating percentage increase or decrease. It's built for students, shoppers, employees, business owners, and anyone who needs a quick, reliable answer without pulling out a calculator app.

X (percentage) — for "X% of Y"

Y (value) — for "X% of Y"

Old value — for % change

New value — for % change

Guide: How It Works

X% of Y = (X ÷ 100) × Y; Increase/Decrease % = ((New − Old) ÷ Old) × 100

Who Is This Calculator For?

Shoppers comparing discounts
Students and professionals tracking growth or change

Examples

What is 20% of 150? (20 ÷ 100) × 150 = 30.

How to Use the Percentage Calculator (Step-by-Step)

Choose your calculation type: percentage of a number, or percentage increase/decrease.
Enter your numbers into the fields provided (e.g. the original number and the percentage, or an old and new value).
Click Calculate to process your inputs.
View your result immediately, along with the formula used.
Adjust any number and recalculate instantly to test multiple scenarios.

Real-World Examples

Shopping discount: a jacket costs $80 and is on sale for 25% off. 80 × 0.25 = $20 off, so the final price is $60.
Exam score: a student answers 42 out of 50 questions correctly. (42 ÷ 50) × 100 = 84%.
Salary raise: an employee earning $50,000 gets a 6% raise. 50,000 × 0.06 = $3,000, bringing the new salary to $53,000.
Restaurant tip: a $65 bill with an 18% tip: 65 × 0.18 = $11.70 tip, for a total of $76.70.
Weight tracking: someone drops from 200 lbs to 180 lbs, a percentage decrease of (200-180)/200 × 100 = 10%.
Investment growth: an investment grows from $10,000 to $11,500, a percentage increase of (11,500-10,000)/10,000 × 100 = 15%.
Sales tax: a $45 purchase with 8% sales tax: 45 × 0.08 = $3.60 tax, for a total of $48.60.

Benefits of Using the Percentage Calculator

Saves time compared to manual percentage math
100% accurate — eliminates arithmetic errors
Free & private — no sign-up, no data stored
Works on mobile, tablet, and desktop
No formulas to memorize
Handles discounts, increases, decreases, and ratios in one tool
Instant results with no waiting

Percentage Calculator vs Manual Calculation

Feature	Our Percentage Calculator	Manual Math
Speed	Instant results	Takes 1-3 minutes
Accuracy	Always precise	Prone to arithmetic errors
Effort	One click	Requires formula recall
Cost	Free	Free, but time-consuming
Device support	Works on any device	Requires paper/calculator

Troubleshooting Common Issues

Problem: I got a negative result.

Solution: A negative result means a decrease. For example, going from 100 to 80 gives -20%, meaning a 20% decrease — this is expected behavior, not an error.

Problem: My percentage doesn't match my calculator app.

Solution: Double-check which values you entered as the 'old' versus 'new' number — swapping them changes the result significantly.

Problem: I'm getting a decimal instead of a whole number.

Solution: Percentages often include decimals (e.g., 33.33%) for precision. Round as needed for your use case.

Problem: The tool isn't loading on my phone.

Solution: Refresh the page or clear your browser cache — the calculator works on all modern mobile browsers without an app.

Frequently Asked Questions

What is the formula for percentage increase?

((New − Old) ÷ Old) × 100, expressed as a percentage; negative results indicate a decrease.

Can this calculator handle negative numbers?

Yes, for increase/decrease calculations, though 'percentage of' inputs are typically positive.

Is this percentage calculator free to use?

Yes, it's completely free with no hidden fees, sign-ups, or usage limits.

Is my data private?

Yes. All calculations happen locally in your browser — no numbers you enter are sent to or stored on any server.

How accurate is the calculator?

It uses precise floating-point math, so results are accurate to multiple decimal places every time.

Can I use this on my phone or tablet?

Yes, the calculator is fully responsive and works smoothly on any mobile device or browser.

Do I need to install anything to use this calculator?

No installation is needed — it works directly in your web browser.

About the Author

This tool is built and maintained by John Britto, a Full-Stack Developer with over 5 years of experience building secure web applications. Our mission is to provide free, private, and reliable tools for everyone.