How do I calculate what percent one number is of another?

Divide the part by the whole and multiply by 100. For example, 30 out of 150 is (30 / 150) × 100 = 20%. Our calculator does this instantly in the "X is what percent of Y" mode.

How do you calculate percentage increase or decrease?

Subtract the old value from the new value, divide by the old value, then multiply by 100. A positive result is an increase, a negative result is a decrease. Enter both values in the "percentage change" mode.

Is my data sent anywhere?

No. Every calculation happens locally in your browser using JavaScript. Nothing you type is uploaded, logged, or stored on any server.

Percentage Calculator

Calculate percentages three different ways without touching a spreadsheet or reaching for your phone’s calculator.

What is a Percentage Calculator?

A percentage calculator is a small utility that handles the three most common percentage questions people run into every day. It can tell you what a percentage of a number is, express one number as a percentage of another, and measure the percentage change between two values. Because every calculation runs directly in your browser, you get an answer the instant you finish typing, and none of your numbers ever leave your device.

How to Use

Pick the calculation mode that matches your question.
Enter the two numbers the mode asks for.
Read the result, which updates automatically as you type.
Adjust either value to explore different scenarios.

The three modes are:

Percent of a number — find, for example, 15% of 200.
X is what percent of Y — find what percentage 30 is of 150.
Percentage change — find the increase or decrease from an old value to a new value.

Use Cases

Percentages show up constantly. Shoppers use them to check whether a sale price is really a good deal. Students calculate their score as a percentage of the total marks. Investors and analysts track the percentage change in a stock, a budget line, or monthly revenue. Teachers convert raw marks into grades, and small business owners work out margins and markups. Having all three calculation types in one place means you do not have to remember which formula applies to which question.

Why Use This

This tool runs completely on your device using client-side code, so your figures are private and results are instant. There is no sign-up, no waiting, and no clutter. Whether you are double-checking a discount, grading a test, or reporting growth, you get a clean, accurate answer in a single step.

Understanding the Formulas

The math behind percentages is simple once you see it laid out. To find a percentage of a number, multiply the number by the percentage divided by 100. To express one number as a percentage of another, divide the first by the second and multiply by 100. To find percentage change, take the difference between the new and old values, divide by the old value, and multiply by 100. Knowing these three relationships covers the vast majority of real-world percentage problems.